WHO/CDS/CSR/EDC/2000.5 UNAIDS/00.03E Distr.: General Original: English UNAIDS/WHO on Global HIV/AIDS and STI Surveillance Group Working Guidelines for Second Generation HIV Surveillance
WHO
UNAIDS
WHO/CDS/CSR/EDC/2000.5 UNAIDS/00.03E Distr.: General Original: English
Second generation surveillance for HIV: The next decade
World Health Organization Joint United Nations (WHO) Programme on HIV/AIDS (UNAIDS) Global surveillance of HIV/AIDS and sexually transmitted infections (STIs) is a joint effort of the World Health Organization (WHO) and the Joint United Nations Programme on HIV/AIDS (UNAIDS). The UNAIDS/WHO Working Group on Global HIV/AIDS and STI Surveillance, initiated in November 1996, is the main coordination and implementation mechanism for UNAIDS and WHO to compile the best information available and to improve the quality of data needed for informed decision-making and planning at national, regional and global levels.
The World Health Organization and UNAIDS would like to thank all the national and international experts who have contributed to the development of “Second generation HIV surveillance” and provided precious inputs and suggestions for this document. The concepts and details presented in this document were discussed during a series of workshops and meetings with the participation and input of national programme managers and experts, staff from bi-/multilateral donor agencies (USAID, GTZ, DFID, EC), field staff of UNAIDS and its Cosponsors, and international experts from a series of institutions such as the Harvard School of Public Health, US Bureau of the Census, European Centre for the Epidemiological Monitoring of AIDS, Centers for Disease Control and Prevention, the Wellcome Trust Centre for Infectious Diseases at the University in Oxford. Special thanks go to Elizabeth Pisani for her contribution to the preparation and the final editing of the document.
© World Health Organization and Joint United Nations Programme on HIV/AIDS, 2000
This document is not a formal publication of the World Health Organization (WHO) or UNAIDS, and all rights are reserved by the Organizations. The document may, however, be freely reviewed, abstracted, reproduced or translated, in part or in whole, but not for sale or use in conjunction with commercial purposes. The views expressed in documents by named authors are solely the responsi- bility of those authors. ii WHO/CDS/CSR/EDC/2000.5 UNAIDS/00.03E
Second generation surveillance for HIV
Table of contents
Executive summary ...... 1
Introduction...... 2
I. The first decade: Lessons learned...... 3 1. Strengths ...... 3 2. Weaknesses ...... 4
II. An overview of data collection methods for HIV surveillance ...... 8 1. Biological surveillance ...... 9 2. Behavioural surveillance ...... 13 3. Other sources of information ...... 16
III. Major indicators used in HIV surveillance ...... 19 1. Biological indicators ...... 20 2. Behavioural indicators...... 20 3. Sociodemographic indicators...... 20
IV. Principles of second generation surveillance...... 22
V. The different epidemic states ...... 24
VI. Surveillance in low-level and concentrated epidemics...... 26
VII. Surveillance in generalized epidemics ...... 32
Annexes — Surveillance for HIV: A step-by-step summary...... 37
References...... 40
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executivesummary
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Second generation surveillance for HIV: The next decade
The diversity of HIV epidemics around the world is becoming ever more apparent. Existing HIV surveillance systems are ill-equipped to capture this diversity, or to explain changes over time in mature epidemics. Efforts are now being made to build on existing systems, strengthening their explanatory power and making better use of the information they generate. Strengthened systems, dubbed “second generation surveillance systems”, aim to concentrate resources where they will yield information that is most useful in reducing the spread of HIV and in providing care for those affected. That means tailoring the surveillance system to the pattern of the epidemic in a country. It means concentrating data collection in populations most at risk of becoming newly infected with HIV—populations with high levels of risk behaviour or young people at the start of their sexual lives. It means comparing information on HIV prevalence and on the behaviours that spread it, to build up an informative picture of changes in the epidemic over time. It also means making best use of other sources of information— communicable disease surveillance, reproductive health surveys, etc.—to increase understanding of the HIV epidemic and the behaviours that spread it. This document suggests classifying the epidemic into different states—low- level, concentrated and generalized—depending on the prevalence of the virus in various population sub-groups. The most efficient mix of data collection for surveillance will depend on the epidemic state in a country. The recommended choice of populations among whom data are collected will vary from epidemic to epidemic; so will the mix of behavioural and bio-medical surveillance. Data use will also vary according to the epidemic state. Where HIV is uncommon, biomedical surveillance and especially behavioural data can provide early warning of a possible epidemic. Where it is concentrated in sub-populations with high-risk behaviour it can provide invaluable information for designing focused interventions. In generalized epidemics it can help indicate the success of the response and provide information essential for planning care and support. In all epidemic states, surveillance systems aim to provide information that will increase and improve the response to the HIV epidemic. This document provides an overview of the principal issues which need to be considered in strengthening surveillance systems and increasing their utility. It suggests priority approaches for the various epidemic states. Technical guidelines are provided in separate documents.
1 introduction
Second generation surveillance for HIV: The next decade
Introduction
Goals of second generation surveillance systems summary a
• Better understanding of trends over time • Better understanding of the behaviours driving the epidemic in a country • Surveillance more focused on sub-populations at highest risk of infection • Flexible surveillance that moves with the needs and state of the epidemic • Better use of surveillance data to increase understanding and to plan prevention and care
A decade has passed since the initial guide- first decade of surveillance, strengthening and lines on HIV surveillance were drafted by WHO in expanding existing systems to achieve the goals of 1989. As HIV continues to spread around the second generation surveillance. world, it has become increasingly apparent that the epidemic does not follow the same course in all This document reviews the achievements of societies. Rather it affects different geographical the first decade of surveillance for HIV. It describes areas and population sub-groups in different ways the strengths and weaknesses of existing systems at different times. and outlines the basic principles of second generation surveillance systems. It then goes on to This complicates the task of monitoring its make recommendations for meeting the surveil- course, intervening to prevent the further spread of lance needs of countries in different epidemic states. HIV, and planning to minimize its impact. It also makes a thorough understanding of the nature of This document is intended to guide policy on each country’s epidemic more vital than ever. strengthened surveillance for HIV. Technical guidelines for the various elements of surveillance— Such an understanding can only be achieved HIV and AIDS case reporting, field guidelines for with more information about who is most at risk in serosurveillance for HIV, sexually transmitted a country, and which behaviours put them at risk. infection (STI) surveillance, and behavioural data Solid behavioural data will identify sub-popula- collection are being published separately as part of tions at risk and will help focus serosurveillance* this series. Existing technical guidelines are listed in resources where they will yield maximum informa- the References. Many of these documents are tion about the epidemic. Behavioural data also help currently under revision. Finalized versions are explain trends in prevalence in mature epidemics. posted on the web sites of the organizations Second generation surveillance systems aim at involved as they become available, and web sites are monitoring trends in behaviour as well as HIV also listed in the References. infection. They build on the lessons learned in the
* In this document, serosurveillance refers to surveillance for HIV antibodies in all body fluids, not just blood.
2 path, butthatunfoldsindifferentways epidemic thatdoesnotfollowasingle,inevitable build astheytrybettertomeettheneedsofan upon whichsecondgenerationsystemsshould the firstdecadehavedemonstratedmanystrengths various population sub-groupsprompted political, credible informationabout levelsofinfectionin invisible. Insomecountries thepublicationof appear, duringwhichtheepidemicremains before largenumbersof AIDS casesbeginto This isespeciallyimportantgiventhelongyears countries forgeneratingapublicresponsetoHIV. a publicresponsetoHIV Surveillance cangenerate Strengths 1. a summary • Systems have difficulty explaining changes in levels of HIV infection in mature epidemics mature in infection HIV of levels in changes explaining difficulty have Systems • infection little where population general the in targeted often are resources Surveillance • ignored often is sources other from information Useful • signs warning provide that behaviours risk the track rarely systems Current • response national the of success the monitors It • responses plan and activities prevention target helps It • HIV to response public a generate helps Surveillance • The approachestaken toHIVsurveillancein decade: first I. The Surveillance datahavebeencrucialinmany or in countries where therapy exists therapy where countries in or neglected are sub-populations at-risk while exists, HIV of spread the for 2. Weaknesses 2. 1.Strengths Lessonslearned Strengths and weaknesses of existing systems existing of weaknesses and Strengths hope tofillsomeofthesegaps. behaviours thatspreadit.Secondgenerationsystems epidemic anditsrelationshiptochangesinthe shown gapsinunderstandingthecourseof countries. Past effortsatsurveillance havealso low inbothcountries. established, contributingto keeping theepidemic behaviour beforethevirus couldbecomewell This earlyinterventionhas helpedpromotesafe first reportedandriskbehaviour wasconfirmed. prevention campaignssoonafterHIVinfectionwas national leadersseizedtheinitiativeandbegan and Senegal,illustratethispoint.Inbothcountries, into amorevisibleAIDSepidemic. further spreadevenbeforetheHIVepidemicturned religious andcommunityleaderstoactprevent Two verydifferentcountries,Switzerland WHO/CDS/CSR/EDC/2000.5 WHO/CDS/CSR/EDC/2000.5 UNAIDS/00.03E
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Second generation surveillance for HIV: The next decade
Behavioural data that pinpoint risk behav- resources to areas most affected, and strengthening iour in the general population can be a valuable social and orphan support systems. complement to HIV prevalence data in motivating action, as the case of Thailand has shown (see below). Surveillance helps monitor the success of the national response Surveillance data help target prevention activities Surveillance systems by definition monitor trends over time. Serosurveillance monitors trends in One of the most important uses of surveil- infection, while behavioural surveillance monitors lance data is to direct efforts to slow the spread of trends in the behaviours that lead to infection. HIV. Surveillance data can demonstrate who is infected and who is at risk of infection, identifying Taken together, data generated by these two sub-groups in need of active prevention programmes. branches of surveillance have been able to give an indication of the impact of national efforts to Perhaps the most useful data in targeting reduce HIV infection and increase safe behaviour. prevention activities are behavioural data. There In Uganda, for example, later age at first sex and are several examples of countries that have rising condom use recorded in repeated behavioural successfully used behavioural data to focus their studies were reflected in lower infection rates in prevention activities. In Thailand, for instance, the young women. The publication of this information, publication of behavioural surveys showing that a demonstrating the success of prevention initiatives quarter of all men visited sex workers, coupled with among adolescents, provided important public the publication of information about high levels of support for continued efforts in this sometimes HIV infection among sex workers, led to a success- controversial area. ful national prevention campaign promoting 100 percent condom use with sex workers.
Despite such demonstrable successes, behav- 2. Weaknesses ioural data collection has often not been integrated into regular surveillance systems. Current systems provide poor early warning Surveillance helps in planning to reduce the impact of HIV and AIDS In the early years of HIV and AIDS surveil- lance, systems tracking the epidemic have focused Since HIV infection typically takes many largely on tracking the spread of the virus itself years to develop into symptomatic illness, the through sentinel surveillance, or have relied on impact of the epidemic is not seen for some time AIDS case surveillance. While these aspects of after HIV infection levels begin to rise. surveillance remain essential, they record infections that have already taken place and so miss the Surveillance data provide the inputs for opportunity to give early warning of potential for models from which national estimates of infection, infection. and projections of the illness and death that inevitably follow, are derived. National estimates Early warning systems are based mainly on and projections have proven extremely useful in data which record risk, rather than actual HIV raising awareness about the epidemic. They are also infection. Risk data such as recording unprotected extremely valuable for planning to mitigate the sex with multiple partners or sharing of unclean impact of the epidemic, for example by redirecting injecting equipment may come from different
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sources: behavioural surveys or other biological infection, (sex workers and their clients, drug markers (e.g., STI for unprotected sex). In the injectors, STI patients, or men who have sex with Russian Federation, for example, little behavioural men, for example) the epidemic may spread data has yet been collected in the general popu- significantly before it is detected. One of the lation. However a dramatic rise in syphilis difficulties in reaching these sub-populations is that infection—from fewer than 10 cases per 100,000 most are marginalized by society at large, and are people in 1988 to over 260 cases a decade later, has poorly served by the institutions that could provide caused alarm about the potential for the spread sentinel sites for HIV surveillance. In many of HIV. developing countries, HIV epidemics remain concentrated in sub-populations at risk; trends in Current systems do not make best use of infection in these populations will not be captured available information from other sources by sentinel surveillance systems designed to track infection in the general population. In low-level Until recently, HIV sentinel surveillance and epidemics, even sentinel systems in high-risk popu- AIDS reporting have been the main sources of lations may show no clear trends in HIV infection. information about the epidemic. Data from other sources—including STI information, behavioural Current systems cannot explain studies and mortality data—have not been changes in mature epidemics systematically included in the HIV surveillance systems. The results of syphilis testing among In the early years of an HIV epidemic, rising pregnant women, for example, are rarely compiled prevalence is almost always driven by a rise in new and used as indicators of risk behaviour by HIV infections. But as time goes on and the virus surveillance systems. Regular surveys of reproduc- establishes itself more firmly in populations tive health such as the Demographic and Health vulnerable to infection, the equation starts to Surveys (DHS) contain data that can be used to change. In mature epidemics, HIV prevalence track changes in sexual behaviour and condom generally begins to level off or to fall. This is often use. But again, these rich sources are rarely used presented as good news: prevalence is stabilizing, systematically by AIDS programmes to comple- the worst is over. The truth, however, may be far ment their surveillance systems. more complex.
Current systems may ignore Stable prevalence implies that there is one at-risk sub-populations new infection for every person who drops out of the group being tested for HIV. So stabilizing In many countries, surveillance systems prevalence may reflect changes in the rate at which have centred on the general population. Blood people drop out of tested groups, because they have taken from groups thought to be broadly died or because they are too sick to come to a representative of the general population, such as testing site, for example. People may also drop out blood donors or pregnant women, has been tested, of testing because they are abstaining from sex or and where negligible levels of infection have been consistently using condoms and so are no longer at found it has been assumed that the epidemic is still risk of pregnancy or STI that would bring them to at an early stage or that no epidemic exists. a sentinel clinic. HIV may also have an impact on inclusion in sentinel populations. It is known, for In truth, however, HIV may already be at example, that HIV-infected women are less likely to epidemic levels in sub-populations not reflected in become pregnant than HIV-negative women, and the groups tested. Unless a specific effort is made to that their relative infertility increases with the search out sub-populations at high risk of duration of their infection.
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Second generation surveillance for HIV: The next decade
Stabilizing HIV prevalence recorded in In these situations, countries are increasingly sentinel surveillance may result from: introducing HIV surveillance and HIV case report- • Stabilizing new infections; ing. HIV case reports are even harder to interpret • Rising death; than AIDS case reports, since it is not possible to know how representative those who are tested are • Lower likelihood of being tested in a sentinel of the whole population. Even trends over time are site through infertility or behavioural change; hard to interpret, since changes in access to testing, • Changes in the age structure of infection, access to therapy, perceived effectiveness of especially relative to the age structure of the therapy, reporting regulations and other factors sentinel population; may affect people’s willingness to be tested for HIV. • Changes over time in the population being tested in sentinel sites; Current systems rarely • Changes over time in the survival time of change with the epidemic people infected. When it first became clear that HIV was a Simply recording changes in HIV prevalence global phenomenon, it was assumed that the does not contribute to an understanding of which epidemic would follow roughly the same course in of these factors may be responsible for the change. all countries. Later, epidemics were described in Well-designed behavioural surveillance is needed two general types: Pattern One, driven by homo- to help explain changing trends in prevalence. sexual men and/or injecting drug users, and Where possible, surveillance systems may need to Pattern Two, largely heterosexual epidemics. focus their attention on new infections, where many of the factors listed above do not come into But HIV is too complex to fit into these neat play. categories. In some countries, the virus has remained contained in small, well-defined sub- Current systems are confused populations. In others, it has spread from those by therapy, where it exists sub-populations to a larger population of sexually active adults who would not consider themselves at In industrialized countries, surveillance high risk of infection. In still others, there are systems have concentrated more on AIDS case several simultaneous but relatively discrete epi- surveillance than on HIV sentinel surveillance. demics in different sub-populations, as well as in the When HIV infection led inevitably to AIDS in a wider population with less obvious risk behaviour. relatively predictable time frame, this system gave a reliable, if belated, profile of infection. In A country’s surveillance needs will vary addition, since most people with an AIDS-defining according to its epidemic state. Although it is by no illness in industrialized countries come into contact means inevitable, an epidemic can shift rapidly with the health systems at some point, this system between one state and another, and the surveil- captured a high proportion of overall cases. lance system should be flexible enough to shift However, with the advent of therapies that slow the with it. For example, if an epidemic is thought to progression from HIV to AIDS, the interpretation of be concentrated in men who have sex with men AIDS prevalence data and its relationship to trends but a growing number of reported HIV and AIDS in HIV infection has changed. It is not yet known cases are in women, surveillance systems should whether, in an age of therapy, there will be any begin to track risk behaviour and identify sources predictable pattern in progression to AIDS or in of infection in the heterosexual population. If a survival with AIDS that would help in interpreting heterosexual epidemic consistently records infection AIDS prevalence data. rates of over one percent in antenatal clinics in
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urban areas, sentinel surveillance sites should be Often, in the past, data generated by added in rural areas. surveillance systems have not been used as well as they might have been. Sometimes this has been This document proposes modular surveil- because information about risky sex and drug- lance systems, elements of which can be added or taking and the infection they lead to is considered dropped according to the shifting needs of the too sensitive for public discussion. Data are not epidemic. published until the epidemic is too serious or widespread to escape public notice. Often, however, Current systems do not always data have simply not been presented in a way that make best use of surveillance data end-users might understand or act on.
Data collection is not an end in itself. The Different users have different needs, and main purpose of tracking an epidemic is to provide these should be anticipated in packaging data for the information needed to change its course. policy-makers and the public. An education ministry Second generation surveillance systems provide planning a reproductive health curriculum might information that helps identify who is at risk of be interested in behavioural data for young people, infection and what behaviours put them at risk. But for example, while private sector corporations unless that information is used to design preven- planning their training needs and insurance tion programmes focused on those most at risk or liabilities might want to see prevalence data broken most likely to benefit, and to plan for care and down by economic region—mining areas, the support needs brought about by the epidemic, the industrial belt, agricultural provinces—rather than effort is wasted. by more familiar provincial or rural/urban criteria.
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II. An overview of data collection methods for HIV surveillance
Second generation surveillance systems do methods have been in use over the past decade, not propose any radically new methods of data although some are more widely used than others. collection. Rather, they focus existing methods on appropriate populations and sub-populations, and Second generation systems aim to expand combine them in ways that have the greatest the use of some of the more rarely used methods, explanatory power. particularly behavioural data collection. Recom- mendations for the appropriate method mix for This section describes the main data collec- each epidemic state are made later in this tion methods used in surveillance. All of these document.
Data collection methods for HIV surveillance summary a
1.Biological surveillance • Sentinel serosurveillance in defined sub-populations • Regular HIV screening of donated blood • Regular HIV screening of occupational cohorts or other sub-populations • HIV screening of specimens taken in general population surveys • HIV screening of specimens taken in special population surveys
2. Behavioural surveillance • Repeat cross-sectional surveys in the general population • Repeat cross-sectional surveys in defined sub-populations
3. Other sources of information • HIV and AIDS case surveillance • Death registration • STI surveillance, TB surveillance
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1. Biological surveillance who choose to know their results. Every effort must be made to ensure that populations among whom Sentinel serosurveillance surveillance is conducted—and indeed all popu- lations—have easy access to voluntary counselling The purpose of sentinel HIV serosurveillance and HIV testing. is to track HIV infection levels in populations accessed through “watchpost” institutions. These Surveillance systems set up to track the institutions are generally selected because they course of the HIV epidemic test all samples taken provide access to populations that are either of in as short as possible a time frame, usually two to particular interest in the epidemic, or representative eight weeks. The short time period is intended to of a larger population. avoid the same individuals being included in the testing population more than once, and to provide In general, sentinel institutions are already an estimate of point prevalence—the prevalence of drawing blood for another purpose. STI patients, infection in a given population at a single point in drug users and pregnant women are all likely to time. Serosurveys in sentinel populations are give blood for diagnostic reasons. Some groups usually repeated annually. such as military personnel or workers in chemical industries may have blood taken as part of a In populations where access is difficult and routine health check-up. Blood given to transfusion sample sizes are small (for example, among drug services has also been used to check levels of injectors newly admitted to treatment programmes) infection among donors. These are not strictly it may take a longer time to recruit large enough speaking sentinel populations, but data generated samples to give statistically meaningful results. by such regular screening can be used in much the In these cases, point prevalence figures might same way as sentinel surveillance data. be replaced by period prevalence, measured over a stated time period. While this is less than ideal, Where blood is taken for other purposes, it is sometimes a practical solution in difficult leftover sera can be stripped of all identifying circumstances. markers and tested for HIV infection without the consent of the individual concerned. This is known How representative as unlinked, anonymous testing. Because the are sentinel populations? individual's consent is not required, biases intro- duced when people refuse to allow their blood to One of the biggest difficulties encountered be tested are minimized. in tracking the spread of HIV is determining the extent to which the population tested is repre- Where blood or other specimens such as sentative of any larger population. In interpreting saliva or urine are being taken specifically for HIV results of sentinel surveillance, programme man- testing, individuals providing the specimens should agers and others need to estimate firstly the extent be informed of the purpose of sentinel surveillance, to which the people tested are representative of the and must give their consent before their specimen sentinel population from which they are drawn, is tested. Even where consent is sought, sentinel and secondly the extent to which the sentinel surveillance samples are generally stripped of population is representative of any broader popula- identifiers so that the result can never be traced tion, or indeed of the general population as a whole. back to an individual, so protecting privacy. Voluntary anonymous testing is increasingly used These issues are discussed for individual in conjunction with a simultaneous offer of sentinel populations below. But using women voluntary counselling and free testing for those tested at antenatal clinics as a general example, the
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first task is to determine whether women tested Trends in infection among STI clinic clients during surveillance activities at such a clinic are must be treated with caution, however. They are representative of all pregnant women in the area not a reliable indicator of programme impact, since served by the clinic. They may well not be, because successful prevention programmes should reduce the sentinel clinic is at a public hospital and risky sex and lead to fewer STIs. People who do wealthier women all go to private doctors, for alter their behaviour may significantly reduce their example, or because since the introduction of user exposure to HIV infection, but they are also likely fees poor women have chosen to forgo antenatal to fall out of the denominator because they will not care completely. get STIs and therefore not seek treatment at clinics.
The next task is to determine the extent to In addition, prevention programmes and which pregnant women represent all women in the other factors may change the profile of those population. Obviously women who are pregnant attending clinics. In many countries, people over- have recently had unprotected sex, so they are in whelmingly favour private clinics or self-medica- fact not likely to be representative of the whole tion for STIs, so government clinics which make up population of women including virgins, those who the bulk of sentinel sites capture only a small and are abstaining from sex, and those who consistently possibly unrepresentative sample of men and use condoms or other methods of contraception. In women with STIs. many societies, pregnant women may be more likely to be in stable partnerships than those using • Intravenous drug users (IDU) contraception. The difficulties of extrapolating data from this sentinel population to the wider Sentinel surveillance in IDU is generally population is discussed at greater length below. linked to treatment clinics. Some countries test injecting drug users who have been arrested and Besides the selection bias described, the imprisoned for their habit. Neither of these representativeness of sentinel populations can be populations is likely to typify the bulk of injecting limited by participation bias. Participation bias drug users who neither seek treatment nor are arises when people who refuse to participate in arrested. There are not many institutions offering sentinel surveillance differ from those who agree to services to drug injectors, so the scope for sentinel participate. This bias is eliminated in populations sites is limited. whose blood is taken for other purposes and from whom consent for unlinked anonymous testing is Several countries have, however, success- not sought. fully used outreach programmes for drug injectors to conduct voluntary anonymous surveillance Sentinel populations using saliva specimens. Refusal rates have been used for HIV surveillance low, and results appear robust. For more infor- mation on the methods used, see WHO’s Guide on • STI patients Rapid Assessment Methods for Drug Injecting, 1998. Patients seeking treatment for STIs are a very useful sentinel population in assessing HIV • Sex workers infection levels among people who have unpro- tected sex with high-risk partners. Data from this For sex workers, too, the major problem is group can act as an early warning system, since access. Health clinics set up in red light districts STI patients are among those at highest risk of especially to meet the needs of sex workers provide acquiring or passing on HIV sexually. an excellent sentinel site for this population, but
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they are rare. Some countries use data from women screening, so the additional procedure of unlinked attending STI clinics in or near “red-light” districts as anonymous testing for HIV on samples taken over a close proxy for HIV prevalence among sex workers. a specified period once a year is an efficient, low- cost method for serosurveillance. In a few countries sex workers must register with the authorities in order to work, and are There are a number of major sources of required to undergo regular screening for STIs. selection bias associated with women attending Regular screening is also provided in a number of antenatal clinics. countries with controlled brothel districts. In such Clinic attendance—As mentioned previously, cases, leftover specimens taken for screening of women who attend the public antenatal clinics STIs may be used for sentinel surveillance for HIV. where sentinel surveillance is generally carried out may differ from those who attend private clinics or It should be noted, however, that illegal and who do not attend clinics. The proportion of unregistered sex workers exist even where sex work women in developing countries who attend ante- is regulated. Sex workers are often illegal immi- natal clinics ranges from over 80 percent in parts grants, non-native speakers of the local language of Africa to under 30 percent in some areas of Asia. or otherwise marginalized compared with registered sex workers. They may also be at higher risk for Fertility—Women who become pregnant may HIV infection. differ from women who do not become pregnant in ways significantly related to HIV infection. HIV • Men who have sex with other men infection itself reduces fertility progressively over time. HIV is often associated with other STIs known In some countries, male-male sex happens to cause infertility. The use of condoms will reduce within well-defined gay communities. These com- both fertility and exposure to HIV. The use of non- munities are generally served by health clinics and barrier contraceptives will reduce fertility, but may other institutions that can be used as sentinel sites. be associated with sex with multiple partners that Elsewhere, however, men who have sex with other increases exposure to HIV. men do not necessarily think of themselves as gay, male-male sex is clandestine, and there are no It should be stressed, however, that studies easily accessed clinics or other sentinel sites for comparing HIV prevalence levels at antenatal communities of men who have sex with men. In sentinel surveillance sites with levels recorded in these situations, surveillance among men who have population-based studies find that antenatal data sex with other men is more difficult. Possible are remarkably robust. In general, in mature approaches include peer outreach services recruit- epidemics, antenatal data tend to overestimate ing men for voluntary unlinked anonymous infection in the younger age groups, while under- testing, or the establishment of health clinics estimating it at older ages. Overall, studies in sub- designed to serve the needs of these populations. Saharan Africa have shown that antenatal data and population-based data are generally very similar. • Women at antenatal clinics Populations regularly screened Antenatal clinics provide the most accessible for HIV infection cross section of healthy, sexually active women in the general population, and have therefore become • Donated blood units or blood donors the most common sites for sentinel surveillance in most developing countries. Blood is usually (but In the early days of HIV surveillance, not always) already being taken for syphilis voluntary unpaid blood donors could also provide
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a fair picture of infection levels in the general healthier, better off, or more likely to work away population, and at no additional cost, since blood from home than men and women in the wider was in any case being screened for HIV under population, for example. And their health, eco- blood safety programmes. Donated blood is, nomic or travel status may be related to their however, becoming less useful for HIV surveillance exposure to HIV infection. because most countries now screen out blood donors with behaviours that put them at higher risk In some countries, the majority of young of HIV infection, and because in some countries men of a given age are required to perform military those with risk behaviours increasingly choose not service. Elsewhere, new recruits to the military are to donate blood as time goes on. chosen by random ballot from the general population of young men in a given age range. In One of the principal advantages of using these cases, new recruits provide a relatively data from donated blood still remains, however. unbiased population for unlinked anonymous HIV Since the blood is already being screened anyway, testing. It should be stressed that the same is not true it is a “free” source of data on HIV prevalence in for cohorts of soldiers; once they have been in the low-risk populations. Recording the percentage of military for some time, young men may be exposed blood units screening positive over a particular to risks or may adopt risk behaviours which are far time period represents almost no extra cost to the from typical of the general population. country. Especially in low-level or concentrated epidemics where HIV prevalence among pregnant women may not be cost effective, it may be the Changes in bias over time only source of information on infection rates in populations not exposed to any particularly If selection and participation bias remain elevated risk of HIV. While the limitations of the similar over time, then trends in infection recorded data should be kept in mind, changes in prevalence in sentinel sites will reflect trends in the population in blood donors or donated blood units can provide represented by those sites. However, bias may useful material for advocacy. change over time. In that case, trends recorded over time may reflect changes in the sentinel population Voluntary blood donors often donate rather than real changes in HIV infection levels. repeatedly. Where there is no coding system that Sources of changing bias over time may include would allow for exclusion of samples given by changes in the fees charged for services, changing repeat donors, it is suggested that the period for in reporting requirements such as the introduction which HIV prevalence in screened blood units is of mandatory named reporting of HIV cases, or the reported for surveillance purposes be limited to a introduction of user-friendly services that attract maximum of three months. Repeat donations in higher numbers of people at risk of HIV infection. this time frame are unusual, so double-counting should be minimized. Cross-sectional serosurveys • Occupational cohorts in sub-populations at risk
Surveillance is sometimes carried out among Sentinel sites as described above exist for occupational cohorts such as factory workers, many sub-populations at high risk of contracting migrant workers or the military, and is often linked or passing on HIV and are the recommended access to regular health checks or to work-based clinics. points for serosurveillance in these groups. These people may differ from the general However, where they do not exist, experience has population in significant ways—they may be shown that repeated cross-sectional HIV surveys
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among members of the sub-population can suc- surveillance sites by testing specimens taken after cessfully be used in order to track HIV prevalence obtaining informed consent from people randomly among people at high risk of infection. Instead of selected from the general population. Sampling is standard venous blood, these may use blood taken usually household-based. on filter paper, saliva or urine specimens. Population-based serosurveillance requires Cross-sectional serosurveys require the informed consent. Experience differs across coun- informed consent of participants. Experience has tries and cultures, but refusal and therefore shown that refusal rates are lowest when peer edu- participation bias has been shown to vary cators and other members of the sub-population at substantially, even when specimens are taken by risk are actively involved in mapping, sampling non-invasive procedures—saliva or urine as and recruitment, and where they are linked to the opposed to blood. provision of services that meet the specific needs of the sub-population. The point of access for cross- General population-based serosurveys can sectional serosurveys is often a nongovernemental be very helpful in indicating possible sources of organization (NGO) or other institution working to bias in sentinel populations. They are expensive and prevent HIV transmission and provide educational, difficult to conduct, and are not recommended as a health or support services to at-risk sub-populations routine part of serosurveillance. However, where such as sex workers or drug injectors. they have been carried out for research or other purposes, their results should definitely be used to While testing may be usually voluntary and calibrate the results of routine surveillance systems. anonymous, the community contact essential to this type of surveillance provides an opportunity to Some countries conduct regular population- offer counselling and confidential testing to those based studies for research or planning purposes in who want it. which blood is drawn (e.g. National Health Surveys, studies on Hepatitis B, malaria, etc. Sampling is often convenience-based, and Demographic and Health Surveys drawing blood the methods by which sampling frames for a for anaemia testing). In such cases, the samples hidden population are established are often not collected can be used for unlinked anonymous HIV clearly described, so care must be taken in extrap- testing. National AIDS programmes should, where olating results to the wider sub-population. feasible, make use of any population-based Whatever methods are used, building up the specimen samples for HIV testing. They will need necessary community contacts and establishing a to try to ensure that the population sampled can be sampling frame is frequently time-consuming and correlated with existing sentinel sites, so that the expensive. While the cost is likely to diminish with two data sets can be compared reliably. This may successive rounds, it may not be practical to repeat require supporting oversampling of the population cross-sectional surveys in high-risk populations with in the area of one or more sentinel sites. great frequency, and their use as part of routine surveillance systems may therefore be limited.
General population-based 2. Behavioural surveillance HIV serosurveys Just as HIV surveillance refers to repeated Population-based serosurveillance attempts cross-sectional serosurveys in a representative to get around selection bias associated with sentinel population, behavioural surveillance refers to
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repeat cross-sectional surveys of behaviour in a Many decades of experience with household representative population. surveys of contraceptive use and reproductive health have shown that refusal bias is usually low There are two major types of behavioural in general population-based surveys that do not survey for HIV: surveys in the general population, involve taking physical specimens. General and surveys in specific sub-populations of interest. population-based surveys of sexual behaviour (also known as KABP studies, or studies of knowledge, attitudes, behaviour and practices) have been General population-based undertaken in a large number of developing behavioural surveys countries since the late 1980s, and have proven useful for advocacy as well as for informing Behavioural surveys of HIV-related behav- programme design and interpreting changing iour in the general population ask a sample of trends in HIV infection in the general population. people about their sexual and sometimes their Integrating HIV and sexual behaviour components drug-injecting behaviours. The sample may be into Demographic and Health Surveys (DHS), restricted to a certain age band and to men or National Health Surveys or other regular survey women. Otherwise, however, general population- rounds can significantly reduce the cost of periodic based surveys usually try to capture the broadest population-based surveys of HIV-related behaviour possible cross-section of individuals. and attitudes. Indeed, after successfully adding AIDS modules to DHS in a number of countries, the The most cost-effective way of achieving international DHS survey programme intends to this broad cross-section is generally to survey include AIDS modules in all future surveys in individuals in a random sample of households in a countries significantly affected by the epidemic. district, province or nation, depending on the scale of the study. Those countries that have repeated national level household surveys of sexual behaviour— General population-based surveys are the Uganda and Thailand, for example—have found most appropriate tool for tracking changes in that establishing trends over time through repeat exposure to risk of HIV infection in the general surveys has contributed significantly to under- population over time. While they may be adapted standing the dynamics of the epidemic. Data somewhat for a particular country situation, they generated by repeat surveys have served as a generally yield rather standardized data that are powerful tool for advocacy, increasing national and comparable over time and geographic areas. They international support for the response to HIV. are useful for investigating levels of risk behaviour and links between the populations with low and higher risk behaviours. However, their ability to Sub-population-based track changes in rare behaviours such as drug behavioural surveys injecting is limited. Certain sub-populations are more at risk of General population-based surveys can also contracting and passing on HIV infection than be very important in monitoring changes in others. Depending on the local circumstances, these behaviour following prevention campaigns. This may include injecting drug users, men who have sex helps in evaluating the combined impact of the with other men, and sex workers and their clients. various components of the national response to HIV: the impact of a single campaign or initiative The behaviour of people in these groups may cannot be determined with this methodology. be critical in promoting or arresting the spread of
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HIV, especially when the epidemic remains concen- techniques in sub-populations must be carefully trated among those whose behaviour carries a documented and conducted in a consistent fashion higher risk of infection. However, they are not easily so that subsequent rounds yield results that can captured in a general population-based survey. illustrate trends with some degree of confidence. The most likely sources of bias should be clearly In the past, behavioural surveys in sub- presented along with the survey results. Sampling populations at risk have generally been linked to methods become more reliable if members of the the design and/or evaluation of specific inter- communities at risk are actively involved in ventions, with no effort made to produce data that mapping, sampling and recruitment. can be used to monitor trends over time. It is strongly recommended that sub-populations be sampled independently of the general population, Bias in behavioural surveys but in ways that allow surveys to be repeated to track changes in risk behaviour over time. Some continue to question whether behav- ioural surveys are useful, arguing that people Sub-population-based surveys generally generally lie about their sexual and drug-taking attempt to define and map the sub-population of behaviours, especially when those behaviours interest, and then reach a random sample of expose them to both social sanction and HIV individuals in that community. This procedure is infection. Certainly, there is a tendency to described in some detail in Family Health downplay “undesirable” behaviour, especially International’s (FHI) Survey Measurement and among women. But several studies have shown Sampling Guidelines for Repeated Behavioural that trends in reported risk behaviour are usually Surveys, Arlington, 1999. reflected in STI trends, that trends in reported condom use are matched by trends in condom Constructing a reliable sampling frame can distribution, and that there is remarkably high be very challenging. In a few countries, sex workers agreement between couples when questioned are grouped into registered brothels that provide a separately about their sexual behaviour. Where ready sampling frame, but in others they operate literacy is high, self-administered anonymous from more hidden sites or operate free-lance. questionnaires may encourage greater honesty on Where populations at high risk of HIV infection the part of respondents than face-to-face inter- such as sex workers and drug injectors exist at the views, where the desire to give “correct” or socially margins of society, random sampling is often not acceptable answers may be stronger. possible. Sampling frames are constructed fol- lowing mapping of sites, but it is often difficult to Behavioural surveys cannot take place ascertain what proportion of existing sites have without the informed consent of the respondent. been mapped, or how many individuals are Experience has shown that, with some exceptions, associated with each site. In addition, even when respondents are more likely to refuse to participate there are clearly defined sites such as brothels, if they are simultaneously asked to provide a access to the sites for interviews is sometimes specimen for HIV testing. denied by the owners or managers. It may also be ill-advised to try to collect Every effort should be made to ensure that behavioural data from people in sites chosen as the survey is as representative as possible of the sentinel sites for HIV testing. For example, sub-population as a whole. Frequently, however, collecting information about recent sexual for reasons of ethics or feasibility, non-random behaviour and condom use from women at sampling techniques are inevitable. Sampling antenatal clinics—that is, women in the later stages
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of pregnancy—is likely to yield results that are far together with predictable information about the from typical of the general population. natural history of infection to “back-calculate” the progression of the epidemic. This procedure was It is therefore recommended that behavioural never common in developing countries, where and seroprevalence data are drawn from different AIDS case reporting is generally far from complete. individuals broadly representative of the same Industrialized countries, too, are searching for source population. This has implications for the data alternatives because antiretroviral therapy is now collected. In order to ascertain the extent to which altering the natural history of HIV infection and the two groups are similar, basic sociodemographic AIDS in unpredictable ways, making AIDS case questions must be asked of each. data much more difficult to interpret. Increasingly, industrialized countries are turning their attention back to HIV case reporting.
HIV and AIDS reporting may be integrated into the communicable disease reporting system. 3. Other sources of information However, data generated by this system are usually rather sparse, concentrating simply on gross There are a number of other types of data numbers of cases. In the case of AIDS, particularly collection that add to the explanatory power of at the start of the epidemic when little is known behavioural and biological surveillance for HIV. about major patterns of risk or of the distribution Some of these are already in place in many of opportunistic infections, a greater breadth countries. Countries may choose to strengthen of information may be particularly helpful. existing systems or begin to add them to behav- Information on the age and sex distribution of ioural and biological surveillance as resources cases, on major risk exposures, and on the allow. distribution of AIDS defining conditions and opportunistic infections can be invaluable in helping to target prevention efforts and plan for HIV and AIDS case reporting appropriate treatment and care needs in a given country or population. Since this level of detail in Many countries have set up case reporting data collection is rarely available in regular systems for AIDS, and some have done so for HIV. communicable disease reporting systems, many In developing countries these systems generally countries have set up special structures for HIV and involve regular passive reporting of AIDS cases and AIDS case reporting. deaths. AIDS case reporting is based on a case definition that may or may not require an HIV Even dedicated HIV and AIDS reporting positive test. For this purpose, several AIDS case systems need to be strengthened if their utility is to definitions have been developed taking into be maximized. Many people living with HIV never account differences in capacities and resources in come into contact with the health system at all countries. In many cases, countries have initially until they develop symptomatic AIDS; so AIDS reported both HIV and AIDS cases, usually case reporting presents an opportunity for abandoning HIV reporting when the number of capturing levels of infection previously unnoticed. HIV infected increased considerably. At the moment, however, poor diagnostic facilities and heavy underreporting, due to weaknesses in Before effective treatment was available, the system and unwillingness to record an HIV or many industrialized countries with relatively AIDS diagnosis because of stigma or loss of complete AIDS case reporting used AIDS case data benefits, all contribute to limit the completeness of
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case reporting. Some countries that have set up In the last few years, however, initiatives to AIDS case reporting systems estimate that they reduce transmission rates from mother to child have actually capture fewer than 10 percent of actual been promoted. These range from short-course cases, and others have no idea how complete the antiretroviral therapy during pregnancy to the reporting system is likely to be, or whether avoidance of breastfeeding in HIV-positive mothers. reporting completeness has changed over time. This clearly limits the utility of case reporting as a tool Unfortunately, the HIV antibody tests designed to track the magnitude of the epidemic, or commonly used for HIV surveillance are of no use even trends over time. in children under around 18 months old, since they may inherit antibodies from their mothers. Tests for Case reporting does, however, have a very the virus itself are complex and extremely important role in advocacy. The HIV epidemic is, in expensive, and are not practical for routine its early years, largely silent. HIV case reporting surveillance of children born to HIV-positive brings to the attention of policy-makers and health mothers in developing countries. At present, planners the existence of the virus in different therefore, the only practical form of surveillance geographic areas and among different commu- that might help evaluate the success of these nities, populations and sub-populations. AIDS case interventions in reducing the rate of vertical trans- reporting does the same for an epidemic in its more mission is AIDS case surveillance among children. developed stages. In many countries, experience has shown that the epidemic is not perceived as Surveillance of paediatric AIDS cases is even “real” until AIDS cases and deaths are recorded. less complete than adult AIDS case surveillance, partly because children often fall ill and die without Case reporting may also contribute to the coming into contact with the health services. validation of data generated by sentinel surveil- Because of the difficulty of establishing serostatus lance. The age structure, sex ratios and reported in young children, paediatric AIDS case definition modes of transmission of both AIDS and HIV cases is complex and many children die before they can can be compared with that of HIV prevalence to be diagnosed. Special efforts should be made to suggest changes over time. Case reporting can also strengthen AIDS surveillance among children and provide information about the presence of the virus to promote fuller reporting of child mortality by in sub-populations that may have been missed by cause of death. existing HIV surveillance systems, suggesting a reappraisal of surveillance needs. Death registration More information on HIV and AIDS reporting is available in the WHO Recommended In countries where vital registration systems Surveillance Standards, Second Edition,1999. are well established, death certificates may provide a source of information about AIDS deaths which can be used to validate data gathered from other branches Paediatric AIDS case surveillance of the HIV and AIDS surveillance system. Careful examination of the age structure of deaths can In the developing countries which are home indicate the influence of HIV. Most HIV deaths occur to nine out of ten of the world’s HIV positive among younger adults, a group in which mortality is children, there is no sentinel surveillance for the generally low. In the absence of other catastrophic virus among children. HIV rates among children events such as war or famine, a dramatic rise in have always been derived from HIV rates among death rates among 15 to 45 year-olds can provide an their mothers. indication of excess mortality due to HIV.
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Death registration suffers from many of the are routinely tested and treated for syphilis in same difficulties as AIDS case reporting—AIDS as a many countries. However data from these cause of death is commonly underreported in most screening programmes are rarely systematically developing countries. However other cause of death collected and used as a surveillance tool for HIV. data—e.g., data on tuberculosis (TB), pneumonia and non-Hodgkin Lymphoma—may be compiled to Countries with routine STI screening pro- give an indication of changing patterns of mortality grammes in any population should work on that may be attributable to HIV-related causes. strengthening reporting systems so that STI data can be integrated into HIV surveillance systems. Other countries with sufficient resources should consider STI indicators setting up STI monitoring systems. The World Health and other biological markers of risk Organization has developed a document, Guidelines for Sexually Transmitted Infections Surveillance, Curable sexually transmitted infections are 1999, to help countries in this task. an important indicator of potential exposure to HIV infection, both because they are co-factors for A recent upsurge in TB infection around the infection and because they indicate unprotected world has been associated with the HIV epidemic. sex with non-monogamous partners. High levels of In some countries, over half of registered TB STIs can act as a warning system for HIV even in patients are HIV infected. Most TB programmes populations where the HIV virus itself is as yet have surveillance systems of their own, or surveil- uncommon. lance for TB is integrated into the communicable disease surveillance system. Sexually transmitted infections generally reflect risk behaviour in the relatively recent past In some countries, TB patients are sys- better than HIV prevalence data, because curable STI tematically tested for HIV because dual infection are usually of relatively short duration. HIV infection may have implications for treatment. There is some may indicate risk behaviour in the recent past, but it evidence that the relationship between rising may equally capture the risk behaviours of several seropositivity rates among TB patients and rising years previously. An increase in safe behaviour is HIV rates in the population as a whole is rather therefore reflected much more quickly in lower STI consistent. HIV prevalence among new TB patients rates than it is in lower HIV rates. It should be borne can help validate trends observed in other sentinel in mind, however, that lower STI rates may reflect populations. It should be noted that, as an oppor- improvements in the quality and coverage of tunistic infection associated with HIV, TB is likely treatment as well as changes in risk behaviour. to develop only after a number of years of HIV infection. HIV rates in TB patients are therefore likely For these reasons, good STI incidence and to be indicative of HIV incidence some years earlier. prevalence data can contribute significantly to tracking trends in risky sex and potential exposure Even when there is no HIV testing, TB data to HIV infection, and to monitoring the success of can be used as an additional source of information measures aimed at promoting safer sex. Many on HIV. In particular, shift in the age pattern of TB countries systematically test for STIs in order to infection over time can act as persuasive evidence diagnose and treat—for example pregnant women of a rise in HIV-associated TB.
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III. Major indicators used in HIV surveillance
The indicators used in HIV surveillance have Most of these indicators should be presented developed over the first decade of surveillance into by age and sex, and some will be presented by a relatively standardized set which allow for other variables such as risk category. They are comparison across time and between geographic described in much greater detail in the relevant areas. technical guidelines.
Major indicators used in HIV surveillance 1.Biological indicators • HIV prevalence • STI prevalence a summary • TB prevalence • Number of adult AIDS cases • Number of paediatric AIDS cases
2. Behavioural indicators • Sex with a non-regular partner in the last 12 months • Condom use at last sex with a non-regular partner • Youth: age at first sex • Drug injectors: Reported sharing of unclean injecting equipment • Sex workers: Reported number of clients in the last week
3. Sociodemographic indicators • Age • Sex • Socioeconomic and educational status • An indicator of residency or migration status • Parity (for antenatal sites) • Marital status
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1. Biological indicators The choice of behavioural indicators may vary slightly according to the group surveyed, but In most cases, HIV and STI prevalence will they will generally include: be reported for the youngest sexually active age groups (15-24) as well as across the reproductively • Percentage of respondents who report at least one most active age range of 15-49. Reporting of HIV non-regular sex partner in the last 12 months; prevalence by five-year age group should also be standard. AIDS case reporting should include a • Percentage who say they used a condom the last number of variables such as age, sex, assumed time they had sex with a non-regular partner, of mode of transmission, AIDS-defining illness, and those who have had sex with a non-regular month of diagnosis and reporting. These criteria are partner in the last 12 months. discussed more fully elsewhere. Hepatitis and TB prevalence may be collected by specialized In addition, the following indicators may be programmes or in the regular communicable considered in specific populations: disease reporting system. • Youth: age at first sex; • HIV prevalence • Drug injectors: reported sharing of unclean • STI prevalence injecting equipment;
• TB prevalence • Sex workers: reported number of clients in last week;
• Number of adult AIDS cases • Sex workers: reported condom use with last client.
• Number of paediatric AIDS cases
3. Sociodemographic indicators
2. Behavioural indicators As has been mentioned, it is recommended that behavioural and biological information should The major behavioural indicators in sexually be collected from different individuals who represent driven epidemics form part of a set of prevention the same source population. In order to compare the indicators (PIs) described in WHO’s Evaluation of a extent to which the tested population and the National AIDS Programme: A Methods Package 1. population questioned about behaviour are in fact Prevention of HIV infection, 1999. Indicators and similar—and to assess systematic differences between questionnaires focusing on risk behaviour among the groups—basic sociodemographic data should be drug injectors are described in WHO’s The Guide collected from both groups. on Rapid Assessment Methods for Drug Injecting, 1998. At present, a minimum of sociodemographic UNAIDS and WHO are currently working data is collected at sentinel sites. The only variables with MEASURE Evaluation and other partners to attached to samples sent for HIV testing are generally update the guide and methods package for age and, where relevant, sex. It is recommended that monitoring and evaluating HIV and AIDS more extensive information be collected from both prevention and care programmes. The joint guide survey populations and at sentinel sites, although the will include revised indicators and updated data constraints on the time of clients and facility person- collection instruments. nel should be kept in mind. At sentinel sites, these
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data should be collected routinely from all clients, population will be possible. It will not, however, be regardless of whether sentinel HIV testing is currently possible to detect systematic differences between in progress. the group tested in the sentinel surveillance period with the wider clinic population. Where samples are large and relatively homogeneous, basic sociodemographic variables The indicators to be collected will vary may be attached to specimens for HIV testing. This according to local circumstances that may dictate allows for comparison of those tested with the the most likely sources of bias. However, they are clinic population as a whole, as well as for likely to include: comparison with the population questioned in behavioural surveys. Questions of confidentiality • Age; should, however, be borne in mind. The more • Sex; descriptive variables attached to a sample, the greater the likelihood of breaches of the anonymity • Socioeconomic and educational status; that is a basic premise of unlinked anonymous sentinel surveillance. Even where sociodemo- • An indicator of residency or migration status; graphic data are not linked directly to a specimen, • Parity (for antenatal sites); a simple comparison of the characteristics of the sentinel site population to the behavioural survey • Marital status.
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Second generation surveillance for HIV: The next decade of 2 of nd generation IV. Principles of second generation surveillance
This document has summarized the state of This section describes the fundamental surveillance systems after more than a decade of principles around which second generation surveil- experience and progress. Clearly, some gaps exist, lance systems are based. Specific recommendations and many of those gaps can be filled by building for different epidemic states are made in the section on and strengthening existing surveillance systems. that follows.
Principles of second generation surveillance summary a Second generation surveillance systems should: • Be appropriate to the epidemic state • Be dynamic, changing with the epidemic • Use resources where they will generate most useful information • Compare biological and behavioural data for maximum explanatory power • Integrate information from other sources • Use data produced to increase and improve the national response
Surveillance systems should be appropriate track this evolution. Where necessary, the surveil- to the epidemic state lance system evolves, expanding its reach or chang- ing its focus to meet changing information needs. Recognizing the heterogeneity of HIV In some cases, such as when the choice of sentinel epidemics around the world, second generation sites is altered to better reflect the national surveillance meets different surveillance needs in epidemic, it will be difficult to produce data that different epidemic states. Surveillance systems are are directly comparable with earlier years. In other designed to answer the needs of a particular country cases, such as when sample sizes among younger situation at a particular point in its epidemic women are increased to give a better idea of trends evolution. in incidence, a subset of data can still be analysed as before to give figures that are directly comparable over time. Surveillance systems should be dynamic, changing with the needs of the epidemic This can be presented simultaneously with data from the strengthened system to give an idea HIV epidemics evolve differently in different of the extent to which any observed changes in situations. Second generation surveillance systems prevalence might be an artifact of changes in the
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WHO/CDS/CSR/EDC/2000.5 UNAIDS/00.03E of 2 of nd generation surveillance system. In making changes to the Information from other sources should be system, countries should always consider the net integrated into HIV surveillance systems gain of data quality in the new system against the cost of losing comparability with earlier data sets. Where other sources of information exist that might contribute information on sexual or Surveillance systems should use resources drug-taking behaviour or exposure to HIV, this efficiently, focusing on populations should be integrated into HIV surveillance systems or sub-populations at particular risk wherever possible. These sources might include surveillance for STIs and TB, as well as death Surveillance systems should focus resources registration systems. where they can provide most useful information. This will often mean tracking behaviour and infec- Information generated by surveillance tion in sub-populations whose members are at high must be used to design and promote risk of contracting or passing on HIV infection. preventative interventions, to plan This focus will vary according to the epidemic for impact and to measure change state, and may shift over time. There is no point at all strengthening Behavioural data should be used surveillance systems unless the data generated are to guide biological data collection made available and acted upon. Data should be and explain trends in HIV infection used to identify sub-populations at risk, to pin- point behaviours which continue to expose people Behavioural data collection is a central part to infection, and to design interventions to reduce of second generation surveillance systems for HIV. those risk behaviours. They should be used to plan Behavioural data should be used to identify which for care and support needs. And they should be populations or sub-populations are at risk of HIV used to measure national progress over time in infection, and to identify where HIV sentinel sur- slowing the spread of the epidemic. veillance should be focused. Biological data derived from HIV surveillance as well as surveillance for The needs of end users should be taken into other biological markers of risk may in turn indicate account when building up second generation where more behavioural data collection is needed. surveillance systems, and data should wherever possible be packaged to meet those needs. Behavioural data should help explain trends observed in biological surveillance. Sampling methods as well as questions asked in behavioural surveillance should be designed with this in mind.
Behavioural and biological data should be used to validate one another
Biological and behavioural data should be used to validate one another. Two sets of data pointing in the same direction make a more convincing case than just behavioural data or HIV prevalence alone.
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V. The different epidemic states
Classification of epidemic states has shifted however, that such a shift is by no means an as the world has learned more about the hetero- inevitable progression. The various epidemic states geneity of HIV. For the purposes of surveillance, are described below. The rationale for categoriza- UNAIDS and WHO suggest a classification that tion is given, followed by a classification based on describes the epidemic by its current state—low- prevalence in different populations. These numerical level, concentrated, or generalized. This typology cut-off points are not rigid scientific classifications. recognizes that a country may shift from one state They act, rather, as a convenient proxy for classifi- to another over time. It is important to stress, cation based on the dynamic of an epidemic.
Three different epidemic states summary a Low-level • Principle: Although HIV infection may have existed for many years, it has never spread to significant levels in any sub-population. Recorded infection is largely confined to individuals with higher risk behaviour: e.g. sex workers, drug injectors, men having sex with other men. This epidemic state suggests that networks of risk are rather diffuse (with low levels of partner exchange or sharing of drug injecting equipment), or that the virus has been introduced only very recently. • Numerical proxy: HIV prevalence has not consistently exceeded five percent in any defined sub-population.
Concentrated • Principle: HIV has spread rapidly in a defined sub-population, but is not well-established in the general population. This epidemic state suggests active networks of risk within the sub-population. The future course of the epidemic is determined by the frequency and nature of links between highly infected sub-populations and the general population. • Numerical proxy: HIV prevalence consistently over five percent in at least one defined sub- population. HIV prevalence below one percent in pregnant women in urban areas.
Generalized • Principle: In generalized epidemics, HIV is firmly established in the general population. Although sub-populations at high risk may continue to contribute disproportionately to the spread of HIV, sexual networking in the general population is sufficient to sustain an epidemic independent of sub-populations at higher risk of infection. • Numerical proxy: HIV prevalence consistently over one percent in pregnant women.
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The issues faced by countries tracking HIV epidemic state. Without surveillance systems, how and risk behaviour differ in different epidemic can a country determine the shape and magnitude states. The remainder of this document is therefore of its epidemic and so know which state it is in? organised around those different epidemic states. It is recommended that each HIV and STI prevention In practice, most countries have some exist- and care programme identify which epidemic state ing surveillance systems or at least know enough the country is in and focus surveillance on the about their epidemic to identify into which broad needs of that state. category it falls. Again, large and diverse countries may tailor surveillance systems to needs at a Although the surveillance needs for low- provincial or lower level, using data generated to level and concentrated epidemics differ, the issues plan and evaluate responses locally within a faced by planners aiming to strengthen systems in national framework. these epidemics are largely similar. Issues faced in low-level and concentrated epidemics are therefore Where no data at all are available, countries discussed together, although separate recommen- should consider following recommendations for low- dations are made for surveillance in the two level epidemics. If these initial surveillance activities epidemic states. reveal that the epidemic has already progressed to a concentrated stage, they can then expand surveil- Obviously, there is a certain circularity implicit lance activities as needed. in designing surveillance systems according to
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VI. Surveillance in low-level and concentrated epidemics
Low-level epidemics are those in which HIV with low-level and even with concentrated epi- infection exists at low levels in sub-populations demics have virtually no systematic surveillance. whose behaviour carries a high risk of contracting or passing on HIV. The virus is not, however, But countries ignore the possibility that risk widespread in the general population. In these behaviour exists at their peril. Some countries have situations, HIV has often not been thought of as a recently seen HIV explode from virtually nothing priority. Even when HIV prevalence rises rapidly in to substantial levels. With no surveillance in place defined sub-populations, countries may fail to it is not possible to identify changes in risk recognize the danger because such populations are behaviour which may lay the groundwork for an often overlooked or marginalized. Many countries emerging epidemic.
Key questions for low-level and concentrated epidemics summary a
• Is there any risk behaviour that might lead to an HIV epidemic? • In which sub-populations is that behaviour concentrated? • What is the size of those sub-populations? • How much HIV is there in those sub-populations? • Which behaviours expose people to HIV in those sub-populations and how common are they? • What are the links between sub-populations at risk and the general population?
Principal goals of surveillance commitment to staving off an epidemic while the in low-level and concentrated epidemics virus is still virtually invisible, or when it is concentrated in marginalized populations such as In both low-level and concentrated epi- sex workers, drug injectors or men who have sex demics surveillance systems can provide early with men who may not strike a chord with policy- warning of risk that might lead to the spread of makers or the public. By looking at indicators of HIV. By definition, little HIV is recorded at the low- risk, surveillance systems should be able to warn of level stage of the epidemic. So surveillance systems the potential for HIV spreading. here rely greatly on behavioural data collection and on other markers of risk such as STIs. Behavioural surveillance data in low-level epidemics can be used to identify who is at high risk Because HIV is usually competing for of infection and which behaviours commonly put attention and action with many other development them at risk. In concentrated epidemics, surveillance challenges, it is often difficult to generate political systems should investigate whether and how
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frequently sub-populations at higher risk interact with behavioural survey guidelines published by WHO, people in the general population of lower risk. Do men UNAIDS and FHI listed in the References. who have sex with other men also have sex with women? Are the clients of sex workers married? How Research and surveillance in sub-popula- many regular and occasional clients do sex workers tions at high risk of HIV infection should try to have? Do they use condoms with some partners but identify not only the behaviours and networks of not with others? risk within those populations, but the links between any defined grouping of higher risk and the general Because people at high risk of HIV infection population. This becomes increasingly critical if the in low-level and concentrated epidemics are often level of infection rises in sub-populations at higher members of marginalized communities, political risk and the epidemic shifts from a low level to a commitment to providing services for them and concentrated state. supporting safer behaviour may be low. Surveil- lance data demonstrating that these individuals The ethics of tracking HIV also interact with people with lower levels of risk in marginalized sub-populations behaviour can, however, help galvanize preventive measures. Active prevention at this stage can help An effective surveillance system requires not minimize the spread and impact of infection in just that sub-populations at high risk be identified, sub-populations at higher risk, keeping the critical but that they be accessible for regular monitoring mass of infection low and averting the spread of of behaviour, risk markers and HIV infection. HIV into the wider community. Perhaps the greatest challenge for surveillance in low-level and concentrated epidemics is gaining It is particularly difficult to interpret stabil- access to these communities in order to track both ization or downward trends in HIV prevalence as behaviour and infection. Community members are an indicator of programme impact in low-level or very often marginalized, and sometimes their concentrated epidemics, since it is impossible to behaviour is illegal. predict what the course of the epidemic would have been in the absence of interventions. If community members fear information about their behaviour (or indeed their HIV status) Focusing surveillance efforts may be used against them, they will either lie to in low-level and concentrated epidemics investigators or refuse to participate in monitoring studies. Successful surveillance in marginalized Surveillance efforts in low-level epidemics communities depends on minimizing participation should focus on tracking behaviour and other bias by ensuring fully informed consent and absolute markers of risk in sub-populations where risk of confidentiality. HIV infection is concentrated. Many successful surveillance efforts in sup- Identifying these sub-populations is the first populations at higher risk of contracting or passing task; a significant amount of formative research on HIV have centred on clinics and educational may have to be undertaken before an efficient programmes designed specifically to meet the surveillance system can even be set up. This needs of people most vulnerable to HIV and its research, which aims to identify sub-populations at impact. These clinics provide services to the risk, to develop appropriate behavioural question- community, and in doing so, provide a sentinel site naires, and to construct sampling frames through at which serosurveillance can be conducted. Where which surveys might be administered, is described sentinel sites do not exist, the advice and partic- in greater detail in the rapid assessment and ipation of community members in designing and
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helping carry out cross-sectional serosurveys have related behaviour in marginalized groups to a been invaluable to successful surveillance. wider audience. Experience has shown that in the early stages of an HIV epidemic, the general Certainly, information gathered for the public’s reaction to information about HIV purposes of surveillance must be shared with the infection in sub-populations with higher risk communities in question to help them mobilize to behaviour is sometimes to call for restrictive and act against the spread of HIV and cope with its prohibitive measures. Experience has equally consequences, and should inform future prevention shown that such measures simply drive risk efforts. However, in low-level epidemics, careful behaviour further underground, making prevention consideration should be given as to whether or not and care programmes more difficult and ultimately to publicize information about HIV infection and encouraging the spread of the virus.
Recommendations for surveillance in a low-level epidemic • Cross-sectional surveys of behaviour in sub-populations with risk behaviour • Surveillance of STIs and other biological markers of risk • HIV surveillance in sub-populations at risk • HIV and AIDS case reporting • Tracking of HIV in donated blood
Cross-sectional surveys unimaginable just a few years earlier. Similarly, in of behaviour in sub-populations at risk parts of China, economic growth is giving rise to increased internal migration, a rapid resurgence of In a low-level epidemic, cross-sectional the sex industry and an increase in STIs. surveys of behaviour in sub-populations at high risk of HIV infection are recommended. The exis- After a sub-population at risk has been tence of these sub-populations—which commonly identified, behavioural surveys should attempt to include sex workers and their clients, the STI track changes in patterns of unprotected sex and patients who are often a proxy for those with high risky drug injecting within the sub-population. heterosexual risk behaviour, drug injectors, and men who have sex with other men—and their Behavioural surveys should collect indica- potential relevance to the local epidemic must be tions of sexual links between sub-populations at confirmed through formative research. high risk and the general population. Behavioural surveys can include direct questions about links Since social circumstances change over time, with people outside the sub-population in question. countries need constantly to re-evaluate the Drug injectors might, for instance, be asked about existence and importance of different sub- sexual partners who are not drug injectors. Sex populations. In Eastern Europe, for example, workers might indicate that their clients are con- rapidly changing social circumstances had led by centrated in occupational groups such as transport the mid-1990s to an epidemic of injecting drug use workers, the military or migrant workers.
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It is also possible to explore links from the HIV and AIDS case reporting opposite side of the risk spectrum, by asking people in the general population about links with sub- Like HIV surveillance, HIV and AIDS case populations at higher risk. For example, men might reporting systems can signal the existence of the be asked in a household survey about contact and virus in a given area or population, and may point condom use with sex workers. to previously unrecognized behaviours or pop- ulation sub-groups that should be included in Since general population surveys are complex further surveillance efforts. and expensive, it not considered cost-effective to set up such surveys simply to look for possible These systems tend to be extremely incom- links between higher and lower risk populations plete, however, and are therefore of limited value in in a low-level epidemic. However, if regular house- describing the magnitude or trends of an epidemic. hold surveys such as the Demographic and Health Surveys are being planned, it would be useful to add Screening of donated blood questions on HIV-related behaviour. In low-level epidemics, widespread routine Surveillance of STIs sentinel surveillance of general population groups and other biological markers of risk is not likely to be cost-effective. Where HIV infection rates in the general population are very STI surveillance in individuals with higher low, huge sample sizes would be needed to detect risk sexual behaviour is recommended at this stage any trends in sentinel surveillance data. The level of an epidemic as a physical marker of unprotected of the epidemic at this stage does not justify the sex with multiple partners. Surveillance of blood- logistic and financial resources needed for such an borne infections such as Hepatitis B and C may be exercise. Routine sentinel surveillance of low-risk useful in tracking risk behaviour among drug populations such as pregnant women is therefore injectors and men who have sex with other men. NOT recommended in low-level epidemics.
HIV serosurveillance Since most countries are in any case in sub-populations at risk screening their blood supply for HIV, data from HIV testing of blood donations can provide a general Sentinel surveillance should be established indication of the level of infection in the general among sub-populations at high risk of contracting or population. However, the interpretation of data passing on HIV. Existing sentinel sites such as drug generated will depend very much on national treatment centres or STI clinics should be used where blood safety policies. possible. When no sentinel sites exist, interventions providing services for sub-populations at high risk Countries that turn away donors who admit may provide an entry point for the collection of to high-risk sexual or injecting behaviour, and that samples for voluntary HIV testing. Cross-sectional inform infected donors to avoid repeat donations, serosurveys of consenting members of the sub- can expect to record very much lower levels of HIV population are also possible. in their donated blood samples than countries that use paid donors or take blood from relatives of sick In low-level epidemics, the initial purpose of people, have no deferral policies and do not inform HIV surveillance is to detect if HIV is present or not in donors of their serostatus. This difference will persist the sub-population being monitored. Unless HIV even where background levels of HIV infection in prevalence is above one percent or so, it may not be two populations with different screening policies are possible to accurately assess trends over time. actually very similar.
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Data collected from blood screening con- However, data from blood donors screening stitute “free” information which can be useful as an need to be interpreted with caution. advocacy tool in low-level epidemics.
Recommendations for surveillance in a concentrated epidemic
HIV surveillance in a concentrated epidemic will contain all of the elements recommended for a low-level epidemic, but will add elements that focus more on the intersection between groups with different levels of risk.
• HIV and behavioural surveillance in sub-populations with risk behaviour • HIV and behavioural surveillance in bridging groups • Cross-sectional surveys of behaviour in the general population • HIV sentinel surveillance in the general population, urban areas
HIV and behavioural surveillance Sometimes, these bridging populations are in sub-populations at risk concentrated in a defined occupational or socio- economic group that is relatively easily identified. The classification of an epidemic state as Mine workers, labourers on commercial farms, concentrated presupposes that the major sub- truck drivers and other transport workers, soldiers populations at high risk of contracting or passing and students are all examples of bridging groups on HIV are known. In these groups, both repeat that have been identified in different countries. cross-sectional surveys and sentinel serosurveil- lance should be carried out as recommended for Behavioural surveys in sub-populations at low-level epidemics. high risk in a low-level epidemic state may already have identified defined groups of partners that may HIV and behavioural surveillance intersect with or act as a bridge to the general in bridging groups population with lower risk behaviour. In a concen- trated epidemic, repeat cross-sectional behavioural Behavioural surveillance among sub-popula- surveys should also be carried out in these bridging tions at higher risk may indicate substantial links populations. They should focus on identifying the with other sub-populations that may in turn relationships and behaviours that threaten to provide a conduit (or bridge) for the virus into the spread HIV to a wider population. general population. The most common of these bridging populations is probably the clients of sex HIV serosurveys among such groups often workers. Men who visit sex workers often have provide warning for the impending epidemic in the wives or other regular partners who would not low-risk population. In many settings, STI clinic consider themselves to be at high risk for HIV. clients represent the overlap between high- and In addition, they may move between populations low-risk populations. High seroprevalence among of sex workers, carrying HIV from one group of STI patients is often followed by increasing HIV women to another across geographical areas. rates among pregnant women. Wherever scope
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exists, sentinel sites should be used for observing relatively low is unlikely to change rapidly. It is trends in HIV among bridging populations. In the therefore recommended that such surveys be under- absence of suitable sentinel sites, repeated sero- taken once every four or five years at most. Where surveys may be considered. possible, relevant questions on sexual behaviour should be added to existing DHS, reproductive Cross-sectional household surveys health or national health survey rounds. of behaviour in the general population HIV sentinel surveillance In addition, it is recommended that behav- in the general population ioural surveys be carried out in the general population, and particularly in young people. These In concentrated epidemics where HIV is well surveys aim to investigate levels of risk behaviour established in certain sub-populations with links to in the general population, gauging the potential for the general population, particularly sex workers, generalized spread of HIV if it were introduced into HIV sentinel surveillance among pregnant women the general population. They also provide a base- should be initiated. The purpose of this surveillance line for assessing future behavioural changes. is to verify whether HIV is indeed following links Behavioural surveys in the general population between sub-populations of higher risk and the should also try to assess links between people with general population and becoming established in the low-risk behaviour and sub-populations in which general population. At this stage, resources for HIV has been shown to be concentrated; in other sentinel surveillance should be concentrated in words, to identify potential bridging populations. areas that reflect likely exposure to populations in which risk behaviour is concentrated. Urban Repeat cross-sectional household surveys of centres, transport centres and locations surround- sexual behaviour are relatively costly. In addition, ing areas of migrant labour such as mines or behaviour in populations where risk behaviour is military camps may prove suitable.
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VII. Surveillance in generalized epidemics
In generalized epidemics, HIV is clearly However, small changes in prevalence in the established in the general population of sexually general population are likely to have a more active adults, with over one percent of pregnant significant effect on the overall impact of the women infected. Although heterosexual transmission epidemic than larger changes in prevalence in is always the dominant mode for the spread of HIV minority sub-populations, simply because the sheer in generalized epidemics, the virus may also be over- numbers in the general population are so much represented in sub-populations with higher than larger. Small shifts in general population average risk behaviour, including drug injectors and prevalence can translate into a massive burden for men who have sex with other men. health services, especially in large countries.
Key questions for surveillance in a generalized epidemic summary a • What are the trends in HIV infection? • To what extent do trends in behaviour explain trends in prevalence? • Which behaviours have changed following interventions and which continue to drive the epidemic? • What impact is the epidemic likely to have on individual, family and national needs?
Principal goals of surveillance and pointing to possible areas of intervention to in a generalized epidemic break the chain of transmission should be an important focus of surveillance work at this stage. The surveillance issues in generalized epidemics differ somewhat from those of low-level The impact of HIV and AIDS will be greatest and concentrated epidemics. The time for early in a generalized epidemic. Surveillance data should warning is passed. Surveillance systems should invest more resources at this stage in data collection rather focus on strengthening their capacity not that helps governments and communities plan for only to track but also increasingly to explain countering the impact of the epidemic. changing trends in HIV prevalence recorded by existing sentinel serosurveillance systems and to Stabilizing prevalence indicate the effectiveness of prevention programmes. Stabilizing prevalence has in recent years By definition, if HIV has become well become a common feature of many of the longer- established in the general population then pre- established generalized epidemics. As has been vention efforts have been less than completely mentioned, stabilizing prevalence brings difficulties in effective, and need strengthening. Demonstrating interpretation. Second generation surveillance sys- which risk behaviours continue to drive the epidemic tems attempt to address these difficulties in two ways:
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• Repeated behavioural surveys examine to be seropositive than men who are found at home. the extent to which trends in behaviour might Having said that, population-based serosurveys contribute to trends in prevalence; remain an important tool for estimating the relationship between HIV infection levels in men and • Sentinel surveillance systems among women. Where they exist, the results of population- pregnant women focus on the youngest age based surveys should be used to guide assumptions groups, where HIV prevalence most closely reflects about the relationship between male and female incidence, or new infections. infections in the general population. AIDS case reporting can also give an indication of the sex ratio Age at infection of infection levels, although AIDS cases will not provide information about recent trends in new In the early part of a heterosexually driven infection. It should, however, be noted that men may epidemic, sexually active people linked in a be more likely to be hospitalized prior to death with network of multiple partnerships are all simulta- AIDS than women, and are therefore more likely to neously at risk of HIV infection. As the epidemic be diagnosed with AIDS. Completeness of reporting matures, however, most of the people whose may therefore be greater for men than for women, behaviour puts them at risk of infection will and the sex ratio of reported AIDS cases should be already be infected. Increasingly, therefore, new interpreted with caution. infections will be concentrated in people who are close to the start of their sexual lives. The urban/rural divide
Verifying levels of infection Many sentinel surveillance systems have and risk behaviour in men chosen or been logistically obliged to focus on major urban areas. But in most generalized The relationship between male and female epidemics, infection quickly spreads from urban prevalence rates in a generalized epidemic is not a areas along major transport routes into the rural simple one. And yet, with the exception of some population. Monitoring trends in rural as well as in occupational-based clinics, sentinel surveillance urban areas is essential for planning appropriate sites are rarely available for men in the general preventative and supportive services. population. Since a large proportion of the population in Most evidence in mature generalized epi- many developing countries lives in rural areas, an demics points towards higher infection rates in idea of prevalence rates in these areas is also young women than in young men. This is partly for essential for making robust national level estimates of physiological reasons, and partly because young HIV infection. women are more likely to have sex with older men, who may have had more exposure to infected Monitoring morbidity and mortality partners in the past. It is more important in a generalized These effects are, however, hard to confirm epidemic than in low-level and concentrated empirically. Even in household-based studies, HIV epidemics to collect quality data on morbidity and infection in men is hard to track with any accuracy. mortality associated with HIV. These data help plan Men are more often away from home than women, for the provision of health and other services such and those that are away (and therefore not captured as orphan support. in a household-based serosurvey) may be dispropor- tionately more likely to have high-risk behaviour and
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Recommendations for surveillance in generalized epidemics
• Sentinel HIV surveillance among pregnant women, urban and rural • Cross-sectional surveys of behaviour in the general population • Cross-sectional surveys of behaviour among young people • HIV and behavioural surveillance in sub-populations with high-risk behaviour • Data on morbidity and mortality
HIV and behavioural surveillance across different geographic or ethnic regions. In in sub-populations at risk others, with homogenous populations differentiated principally by their level of urbanization, for Even where HIV epidemics are well established example, it may be more efficient to concentrate in the general population, sub-populations with urban sites in a single city in order to capture the higher risk behaviour may contribute disproportion- variations between different socioeconomic groups ately to the continued spread of the virus. In a in the urban environment, while rural sites may be generalized epidemic state, this is especially true of distributed according to area of economic activity. sex workers, who have extensive contact with clients In every case, sentinel sites should be selected for who usually have other partners with lower risk. both urban and rural areas. Behaviour change in these groups may also have a disproportionate effect on slowing the spread of the Focus on younger age groups virus. Cross-sectional surveys of behaviour and HIV infection in these groups on an annual basis continue Surveillance efforts in generalized epidemics to play an important part in monitoring trends in the should attempt as much as possible to focus on epidemic. tracking relatively recent infections. Although it is not possible to measure incidence with a regular Sentinel surveillance HIV surveillance system, it is possible to concen- among pregnant women trate resources on younger cohorts whose infection is likely to be relatively recent and less likely to be Besides sub-populations at higher risk, biased by reduced fertility. It is recommended that sentinel serosurveillance systems in generalized keym high volume sentinel sites be identified, and epidemics should generally focus on pregnant sample sizes at those sites be increased consid- women at antenatal clinics. However, several erably to ensure large enough sample sizes for the important steps are needed to increase the utility of 15–24 year-olds. the information gathered at these sites. This will allow improved tracking of spread- Site selection ing infections among the young, while allowing the whole sample to be weighted to ensure direct The selection of sites themselves should be comparability with previous sentinel data. It will reviewed so that they provide an optimum balance also be necessary to maintain sampling among between efficiency, explanatory power and political older women in order to make accurate estimates imperative. In some countries, it may be necessary of HIV infection nationwide. to opt for a wide range of locations (which may increase cost and complexity of data collection) in Since sexual behaviour varies greatly at order to demonstrate the distribution of infection younger ages (and since one of the aims of preven-
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tion campaigns is to encourage a delay in early recorded at antenatal clinics and other sentinel sexual activity) data for these age groups should be sites, to allow for the comparison of populations disaggregated wherever possible by single or two- and the identification of possible bias. year age band. Such disaggregation is likely to be meaningful only in the highest volume sites. In Behavioural surveillance some countries, especially those with lower fertility, among young people it will not be possible at all. Indeed, meeting recom- mendations for larger sample sizes at younger ages In a mature, generalized epidemic, anyone may become more challenging as HIV prevention who has unprotected sex with a partner whose HIV programmes grow more successful in reducing status is not known may be at high risk of young women's exposure to unprotected sex with infection. Saturation of older age groups means multiple partners, since there will be fewer that new infection in such epidemics appears to be pregnancies among young women. Technical concentrated increasingly in younger age groups. guidelines intended to give more information on sample sizes and sampling methods are planned. Establishing safer behaviour from the outset of young people’s sexual lives may be far more Collect data on site effective in altering the course of the epidemic than and population characteristics changing behaviour in older groups. This is not least because young people are more open to new Second generation surveillance systems norms and attitudes than their elders. Many attempt to ensure that data are as comparable as countries work hard to establish safer behaviour in possible, and to describe potential biases in biological young people, and some countries have been or behavioural data collected. To that end, sentinel rewarded by significant falls in both reported risk sites should collect data on basic population behaviour and in HIV prevalence in this group. characteristics. In many antenatal clinics, these data These successes have provided hope and strength- are already collected. As a part of routine HIV ened the resolve of those contributing energy and surveillance, they should be used to compare the resources to preventing the spread of HIV. clinic populations with the general population, and with the population among whom behavioural It is therefore very strongly recommended surveys are carried out. that surveillance systems in generalized epidemics include a component of behavioural surveillance Behavioural surveillance among young people. The exact age groups in the general population covered will vary from country to country. In cultures where sex starts early—where HIV In a generalized epidemic, repeat cross- infection, STI or pregnancy are commonly recorded sectional household surveys are recommended for in adolescents—behavioural surveillance among tracking changes in sexual behaviour. Such surveys young people may start in the early teens. should be conducted every three to five years. The exact mix of questions will depend on particular A rise in the age at first sex is an important risk factors and vulnerabilities in a country, but response to HIV prevention campaigns, so behav- indicators should be selected as far as possible from ioural surveillance among young people should a standardized list so that results are comparable continue through the early 20s. However since over time and place. patterns of marriage, partnership and sexual behaviour may differ significantly over the early Household questionnaires should also record years of people’s sexual lives, it is recommended the same basic sociodemographic information as is that teenagers and the 20–24 year-old age group
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be sampled separately. Household-based surveys much as possible to reflect the areas from which will minimize bias in sampling for both groups. key sentinel surveillance sites draw their clients. In a national or regional household survey of Whereas in the 20-24 year-old age group the behaviour, that may mean oversampling around standard adult questionnaire on sexual behaviour sentinel sites. may be appropriate, modifications are likely to be necessary for teenagers, especially in defining types It has been recommended that second of partnership. However as far as possible, indica- generation surveillance systems attempt to focus tors should overlap with those used in other types of on new infections by increasing sample sizes of surveys to allow for a comparison between groups. younger women at key antenatal clinics. Surveil- lance systems ought to take the location of these Because behaviour changes more rapidly sites into account when planning the household- among young people than among older adults based behavioural surveys of young people that are whose sexual habits are already well established, it recommended as an integral part of surveillance in is recommended that behavioural surveys among a generalized HIV epidemic. young people take place every two years. Indicators of morbidity and mortality Sampling for greater explanatory power Countries with generalized epidemics often A central tenet of second generation sur- face massive increases in incapacitating sickness and veillance is that behavioural and biological death in young adults which have implications for surveillance data be used to inform and explain economic production and family structure, and one another. The power of the two sets of generate increased needs in terms of social and information to illuminate real trends in the medical services. epidemic and the behaviours that spread it is greatly increased if they are designed from the start Data about real levels of sickness and death to be used together. can help countries plan for these needs. At present, HIV and AIDS case reporting and records of AIDS- The collection of data that allow behavioural related death are at best erratic. Efforts should be and biological surveillance populations to be made to strengthen reporting systems to improve compared has been discussed. But there is also their utility to planners and policy-makers. room for increasing the explanatory power of surveillance systems through improved sampling. Better use can also be made of data gener- ated by regular death registration systems in It is important, firstly, that populations recording increases in both adult and child death sampled for behavioural surveillance be chosen as from causes likely to be HIV-related.
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Surveillance for HIV: A step-by-step summary
Low-level epidemics
Main questions Core surveillance Additional surveillance / Studies
Are there groups • Formative research • Mapping to cover a larger with risk behaviour? and mapping of groups geographical area, and to be with potential risk behaviour conducted more frequently
• Analysis of available • Estimate size of groups STI surveillance data with potential risk behaviour
What are the main risk • Risk behaviour surveys • Increased geographical behaviours? in groups considered coverage of risk behaviour at high risk for HIV infection surveys
• STI prevalence and incidence studies in groups with risk behaviour
How much HIV infection • HIV serosurveillance • Larger coverage and increased is there? in identified groups frequency of HIV sero- with risk behaviour surveillance in identified groups with risk behaviour • Analysis of available blood donor HIV screening data • HIV sentinel serosurveillance in pregnant women in urban areas
Who else might be affected • AIDS case reporting • Risk behaviour surveys and to what extent? focused on potential bridging • HIV case reporting populations
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Concentrated epidemics
Main questions Core surveillance Additional surveillance / Studies
How much HIV infection • HIV serosurveillance in groups • Wider geographical coverage is there? with risk behaviour and increased frequency of HIV serosurveillance • Annual HIV sentinel in identified groups with risk serosurveillance in pregnant behaviour women in urban/high exposure areas • HIV serosurveillance in bridging populations and • Analysis of available blood pregnant women donor HIV screening data
What are the main risk • Repeated risk behaviour • Wider geographical coverage behaviours and how surveys in groups with risk and increased frequency of do they change over time? behaviour repeated behavioural surveys in groups with risk behaviour • Repeated risk behaviour and bridging populations surveys in bridging populations • Surveys of health seeking behaviour for STI • Analysis of STI data in groups with risk behaviour and bridging populations
Who else might be affected • Repeated risk behaviour • Repeated risk behaviour and to what extent? surveys in the general surveys in the general population in urban/high population in all areas exposure areas • HIV case reporting • AIDS case reporting
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Generalized epidemics
Main questions Core surveillance Additional surveillance / Studies
What are the trends • Annual HIV sentinel • HIV sentinel serosurveillance in HIV infection? serosurveillance in pregnant in pregnant women in a larger women in urban and rural number of sentinel sites areas • HIV serosurveillance in groups • Increase sample size in high considered at high risk (e.g., volume sites to enable sex workers and their clients) analysis by age groups • Population-based HIV • AIDS case reporting prevalence studies to validate surveillance data
Is behaviour changing? • Repeated behavioural surveys • Larger coverage in groups considered at high of behaviour surveys Do recorded changes help risk of HIV infection explain trends in HIV infection? • Analysis of STI surveillance data in groups considered at high risk of HIV infection
• Repeated risk behaviour surveys in the general population with a focus on young people
• Analysis of STI surveillance data in the general population
What is the impact of HIV? • Vital registration data • Other death data (census and studies) • Surveillance of TB and other HIV/AIDS related illnesses • Studies of access to care
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References
The three principal sources for materials listed here are UNAIDS, WHO and FHI. The latest versions of the published technical guidelines can be found on the internet at: http://www.unaids.org or http://www.who.int or http://www.fhi.org
Technical guidelines
UNAIDS and Family Health International, May 1998: Meeting the Behavioural Data Collection Needs of National Programmes on STD/HIV and AIDS This document discusses behavioural data collection needs by different epidemic state. It reflects recent thinking about the best use of resources in behavioural data collection in the context of second generation surveillance. Family Health International, 1999. Survey Measurement and Sampling Guidelines for Repeated Behavioural Surveys. Arlington. These guidelines focus on sampling frameworks in sub-populations of particular interest for behavioural data collection in HIV epidemics. They include hard to reach populations such as sex workers. UNAIDS/WHO 1999: Guidelines for Sexually Transmitted Disease Surveillance These technical guidelines provide information on STD surveillance in a number of different country settings. They discuss STD case reporting, prevalence assessment and monitoring and assessment of syndromic aetiologies, as well as other aspects of surveillance. WHO Programme on Substance Abuse, 1998: The Guide on Rapid Assessment Methods for Drug Injecting — Draft Includes protocols for assessing HIV prevalence and risk behaviour among injecting drug users. WHO Programme on Substance Abuse, UNAIDS, 1998: The Rapid Assessment and Response Guide on Substance Use and Sexual Risk Behaviour — Draft Focuses more closely on sexual risk behaviour among users of injecting and non-injecting drugs and other substances such as alcohol. Includes information on sampling, and questionnaire development. UNAIDS: Reaching Regional Consensus on Improved Behavioural and Serosurveillance for HIV, 1998 UNAIDS: The Relationship of HIV and STD Declines in Thailand to Behavioural Change, 1998 UNAIDS: A Measure of Success in Uganda, 1998
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