The Transformation of Partner Notification

SUPPLEMENT ARTICLE

The Transformation of Partner Notiﬁcation

Richard Rothenberg Department of Family and Preventive Medicine, Emory University School of Medicine, Atlanta, Georgia Downloaded from https://academic.oup.com/cid/article/35/Supplement_2/S138/314336 by guest on 01 October 2021

Since 1996, several traditional epidemiological studies of program efficacy have done little to alter the fixed opinions of promoters or detractors of partner notification. Modeling studies have appeared that confirm the value of the contact-tracing approach in locating and treating persons who may be important in transmission. These provide a theoretical base for a number of empirical studies that have applied social network methods to classical partner-notification approaches, which have demonstrated the dense networks and geographic clustering of persons involved in sexually transmitted disease transmission and have provided justification for focusing efforts on small groups that may be critical to epidemicity or its maintenance. These initial studies would appear to warrant a broad-based inclusion of network concepts into programmatic activities, with careful monitoring and analysis of the impact they have on both the traditional indices of partner notification as well as the larger effect on disease transmission.

Partner notification (PN), as practiced in sexually trans- to the lack of demonstrable influence of PN on disease mitted disease (STD) control programs, is a multistep transmission. process that begins with eliciting information about Since the appearance of several recent reviews of PN sexual contacts from a person infected with an STD. [1–3], a number of publications have taken a view of Those partners are then notified that they are at risk the process of PN, a view that incorporates concepts for being infected, are assisted in seeking medical care, in social network analysis [4, 5]. Some of these concepts and, if infected, are treated and interviewed. Although have been acknowledged in STD control for years, but implemented under a variety of names and with nu- none has played a central role. merous variations (contact tracing, case investigation, The network-informed approach posits that, in areas partner services referral, self-referral, patient referral, of heightened transmission, a social network with sex- and provider referral), the basic process has been un- ual interactions will contain persons infected from var- changed for 50 years. ious sources. An infected person who happens to be The value of PN continues to bedevil public health interviewed will thus have others in his or her sexual workers and investigators [1]. Many of these people are or social environment who are infected but not nec- deeply committed to the process simply because it is essarily because of sexual contact with the interviewee. enshrined in STD control activities. Others stress its Thus, the friends, associates, and others who are part value to individual infected persons, who can help of a social milieu may be important to pursue, in ad- friends get treatment and prevent their own reinfection. dition to direct sexual contacts. This hypothesis leads Still others emphasize the epidemiological and research to an expanded approach to PN—one that includes value of the process. But a substantial number of voices assessment of nonsexual contacts, selective screening of have raised the question of proven efficacy and point associates in the field, construction of the actual networks of interacting individuals (known in social network parlance as “connected components” [groups of Reprints or correspondence: Dr. Richard Rothenberg, Department of Family and Preventive Medicine, Emory University School of Medicine, 69 Butler St. SE, people wherein everyone is connected to everyone else Atlanta, GA 30303 ([email protected]). by a path of some length]), and visualization and geo- Clinical Infectious Diseases 2002;35(Suppl 2):S138–45 graphic placement of networks as tools for deciding on 2002 by the Infectious Diseases Society of America. All rights reserved. 1058-4838/2002/3508S2-0002$15.00 next epidemiological steps.

S138 • CID 2002:35 (Suppl 2) • Rothenberg In the present article, we review publications during the pe- the United States, a time-allocation study of the elements of riod from 1996 through early 2000 (table 1), noting the more PN in public clinics revealed a similar diversity and lack of traditional approaches that have been taken and the newer systematization in the approach [37]. In the private sector, it activity involving a social network approach that has emerged has been noted that clinicians and their patients are often en- in the evaluation of PN. tirely unaware of the process [38]. Some of those attempting a broader assessment of the value of PN have been positive about the process in general settings [39], for the prevention TRADITIONAL PN APPROACHES of pelvic inflammatory disease (PID) [40], for use with drug injectors [41], and in developing countries with appropriate Program descriptions. Although a number of descriptions of attention to context [32]. Others have been more reserved, program activity have been published in recent years [6–8, 13, often citing a lack of information about cost effectiveness [42, Downloaded from https://academic.oup.com/cid/article/35/Supplement_2/S138/314336 by guest on 01 October 2021 15, 16], they were in the minority. Such descriptions detail the 43] and stressing the need for better information about the well-known difficulties of actually performing PN, particularly practice itself and its effect on outcomes [44]. in suboptimal settings. The enthusiasm for attempting to bring Models and constructs. Only a few authors have focused on PN to third-world environments is considerable but is tem- the value or effects of PN from the perspective of transmission pered by the lack of resources, the newness of the process in modeling. Ghani et al. [31] used a Monte Carlo simulation (a many cultures, and specific objections that relate to required process whereby a large number of networks are generated on training [6, 30–32]. In the developed world, several approaches the basis of values of network parameters chosen stochastically have been offered to organizing program services for STDs, by computer) to create a “true” network picture and sampled including PN [33, 34], and an updated program operations from it using alternative sampling strategies (individual reports, guide for STD control and prevention is currently being pre- snowball sampling, and contact tracing). In a complex analysis, pared by the Centers for Disease Control and Prevention (CDC; they demonstrated that all 3 methods produce biases in the es- J. Wasserheit, personal communication). timation of true network properties (mixing properties and net- Evaluating PN. During recent years, only a few studies of work structure). In general, snowball sampling and contact trac- the effectiveness of traditional PN have been published. In gen- ing provided less biased estimates of mixing matrices, and contact eral, the results were similar to those of studies done in past tracing may be the preferred approach because of logistic features. years [1]. Faxelid et al. [9] demonstrated that individual coun- Several other investigators have studied the cost effectiveness of seling of patients in a Zambian setting improved the contact PN. Rahman et al. [28] estimated that $4930 would be gained index to 1.8, compared with 1.2 in the uncounseled group. Levy per year of life saved through application of PN for HIV in Japan. and Fox [21] demonstrated that injecting drug users were en- Their analysis, however, made assumptions about the effective- couraged to name partners with the help of an outreach team ness of the practice that might be hard to justify from published that assisted in their notification. In a study of PN for syphilis data. Howell et al. [27] used a model to apply cost effectiveness [14], a CDC team determined that 3 intervention groups—(1) to the evaluation of alternative PN strategies for preventing PID self-referral, (2) provider referral by a disease intervention spe- in women. They found that early diagnosis and treatment of the cialist, and (3) provider referral by a disease interventionspecialist female sex partners of infected men prevented more cases and who took blood samples in the field—were no different in their saved more money than the strategy of interviewing infected final outcome. The number of partners brought to examination women for their male sex partners. This strategy, however, did in each group varied from 0.61 to 0.67. In a parallel study of not consider the differential contribution of some men with long- HIV PN [19], the original study design was abandoned because term asymptomatic infection to the overall transmission of chla- of considerable crossover in group assignment, but the investi- mydia [23]. gators were able to show that the cost per new HIV infection identified was $2200. As noted, the low contact indices in these 4 studies, the substantial logistical problems encountered, and NETWORK CONSIDERATIONS the absence of a linkage of the activity to interruption of disease transmission have been characteristic of studies in past years. During the past several years, a number of published articles Commentaries and surveys. Actual studies of PN have been have attempted to examine the network attributes of the PN augmented in recent years by specific inquiries into the par- process and to use network concepts to enhance these proce- ticulars of the process as well as a number of editorials and dures. Some of these have incorporated network concepts with- articles of opinion. Several investigators have documented the out overt reference to the field. For example, Jordan et al. [17], current practices of clinics in the United Kingdom [15, 35, 36] in a brief communication, demonstrated that asking infected and agreed that practices are diverse and continue to hinder persons about their network (as opposed to their contacts) may an evidence-based approach to evaluation of the process. In be of value in finding new cases. In 1 focus group, persons

Transformation of Partner Notification • CID 2002:35 (Suppl 2) • S139 Subjective quality rating lated to PN efficacy only tangentially of programmatic activity program in very difficult setting Good study but re- Good standard study Good Good Good Fair Good description of Data unusable Not usable quality/biases Design analysis Downloaded from https://academic.oup.com/cid/article/35/Supplement_2/S138/314336 by guest on 01 October 2021 0.30 as a mean in both types of counties tics of pts andpartner relationship referral to in the field; results notfor clear-cut most favorable strategy or for overall effectiveness getting patients to participate and in obtaining information; ul- timate result is that 5positives were new found HIV- for 471 pts ! pears to show some increased benefit from individual counseling of pts in this setting numbers of sexual partners of their partners presents some difficulties in accuracy (note: could be treated as abut does model incorporate empirical data) to show efficacy; note that partners notified by case was showed that partners could be named, but only 30% cameclinic and to almost half ofreferred internally those got lost to follow-up low; no mention of diagnostic outcome in contacts; focus on how long it took totacts get in con- clinic were related to domiciliary visit; data appearthat to nothing show was accomplished Enormous detail on characteris- Stability of interventions uncertain Numerous practical difficulties in Well-conducted study that ap- Using testimony from pts on the Ecological correlation, not meant Straightforward description, Data presentation difficult to fol- Unclear that contacts reporting to ϩ 3 others: findings Reported ϫ 2.7) if index tested partners attended, either at STD clinic or elsewhere; 63% and 30% contacts infected 1.1–1.2 partners/index case; 0.610–67 treated; costs $317–$362/case 197 started PN; 70 pts named 158 contacts; 71 contacts notified; 27 in clinic and test; 5 new HIV-positive general, but greater assortativeness among those with high activity, confirming pos- sibility of core groups counties with anon. testing eliminated, more success ( confidentially slip/for M, 85% vs.contacts 55% came of for Rx;65% for W, vs. 56% cametreatment; for slips worked better for W contacts than M ners, 331; M presenting at clinic, 101; M referred, 59; M lost to follow-up, 26 (44%) W named 61 contacts;of 73% contacts seen and examined visits scheduled 28 visit made 11 visited none would reveal other partners; 51 female contacts reported to clinic 90% of pts received contact 1.6 partners/case; 40% of 580 All 3 approaches located Weakly assortative pattern in Similar increases in PN; in 1 W Rx, 384; W named part- 50 M named 58 contacts/50 9371 attended/663 had STD 38 Outcome measures and treated ner treated (Q) county treated to attendance treatment informed, returning, and treated Percentage of contacts found Contact indices, cost per part- Measures of assortativeness Contact indices, by type of Partners referred, partners Contact index/target time Partners in 3 mos/partners Exposure/ intervention card” partner referral back); immediate provider referral; provider referral with field bloods of pts and thetheir patterns contacts, of based on reports of the pts and after change in testing policy termine attitudes of men and women toward STDs and partner referral; infected women asked to refer their sex partners for treatment; evaluation of internal referral services health advisers, 100 pts counseling and contact slips vs. nothing None; observational study Contact indices 471 pts; 353 discussed PN; Observation before, during, Focus groups held first to de- Domiciliary visit for defaulters No. found/no. brought to Randomization to individual type/setting Study population sample without the elimination of anonymous HIV testing The Gambia; men and women reporting with STD symptoms clinic Delhi, India STD clinic in Amsterdam Routine CT with “referral 3 US STD clinicsMedical record review of Partner referral (provider fall- STD clinic pts Determine the82 mixing counties pattern in NC, with and Working class people in New Poor Haitian women; antenatal British GU medicine clinic Standard contact tracing by Study design tice; analysis to look at factors associated with PN outcome PN strategies for syphilis over 12-mos in GUEngland clinics in built from empiric data mented linear regression those lost to follow-up Prospective audit van de Laar et al. [13] Observation of routine prac- Peterman et al. [14] 3-pronged prospective trial of Fenton et al. [15] Prospective survey of HIV PN Garnett et al. [10, 11] Observations; model Kassler et al. [12] Time-series analysis, seg- King et al. [7] Rathore et al. [9] Study of domiciliary visits for Faxelid et al. [9] Intervention-control study Health center clinic in Lusaka, Table 1. Table of evidence from informationCitation on partner notification (PN)Desormeaux published, et al. 1996–2000. [6] Program description

S140 ) continued ( quality assessment) Good Case study of good Good Fair (authors’ own Good Good Good Good Downloaded from https://academic.oup.com/cid/article/35/Supplement_2/S138/314336 by guest on 01 October 2021 but offer a high yieldHIV-positive cases of from new persons interviewed; in particular, 2 network questions (whom do you know who youhaving think risky is sex andyou whom know do who might bepositive) had HIV- a high yieldpreviously undiagnosed of cases ward exploring how best toinfected find persons ecution of the study; groups collapsed to study costs proach, constructing social networks from interview information no testing results provided for assessment of efficacy but focus on preference terns and their connections to population subgroups and the intensity of transmission; several important observations for direction of intervention resources testing validity of current rec- ommendations; found that epidemiologically important people (asymptomatic men with long- term infection) are not identified without extending the traditional interval Standard audit follow-up Results are informally presented Observational study, geared to- Many problems in design and ex- Observational, noninterventive ap- Standard case comparison study; Interesting analysis of mixing pat- Traditional case-finding approach tacts; 17/25 found; 15/17 tested; 12/15 HIV-positive found, 46; M positive, 33; unaware, 9; from these 9, 14 W contacts, 6tive; HIV-posi- from 23 aware: 31tacts con- 22 HIV-positive, 8 unaware of status; (a)identified, 30 17 HIV-positive, 9 unaware; (b) 15 identified; 11 HIV-positive, 8 unaware same from infected and uninfected contacts; source and spread often indistin- guishable; prevented cases easily recognized; major change in network structure during epidemic partners found; 122 newly identified HIV-positive; $2200/new HIV infection tacts connected directly or indirectly to core transmitters groups; 71% of partners in enhanced group referred to outreach time age, education, and partner no. associated with GC and CT; links with high previous subpopulations associated with GC 2293 partners named; 40% examined; 88% identified with adherence to CDC cri- teria; 12% of epi-important persons not so identified PN studies: W infected, 68; M 42% of network sexual con- 142 partners named in both Discordance on race/ethnicity, 1309 pts, 1109 interviewed, 28 pts; 14 identified 25 con- 1070 pts, 8633 partners; 1035 positive, awareness of positivity transmitters” bility; use of outreach team type of mixing; ORscordant for vs. con- discordant relationships; classification as bridges, links, or neither ered by critical period Contact indices; proportion Indices, epidemic description Proportion of infected persons Cost/partner notified Importance of “core General measures of accepta- Mixing matrices to assess Proportion of contacts discov- groups identify (a) persons they think are practicing risky sex and (b)thought friends might they be HIV- positive ing, interviewing infected and uninfected persons, and seeking infected and uninfected contacts observation of frequent crossover among groups network contacts with enhanced (option of having partners notified by outreach group) cal and clinical information on cases and theirnoninterventional partners; grammatic activity None; observational study Contact indices Network-informed contact trac- 10 index interviews for social Compare minimal (self-tell) Observations of epidemiologi- None; review of ongoing pro- Original plans dropped after in UK suburban community clinic sex and drug partners population from private or public health clinics private cases Hospital and STD clinic Routine PN practice; focus Young men and women in 3 STD clinic settings Syphilis pts diagnosed from IDU from the community; both Population from STD center; STD clinic population and HIV-positive pts; GU clinic groups network techniques used different strategies to PN for HIV syphilis cases vs. usual intervention protocols seeking contacts from STD patients with GC or chlamydia finding results Retrospective review of case- al. [23] Jordan et al. [17] Audit of PN program; focus Rothenberg et al. [18] Outbreak investigation; social Toomey et al. [19] 4 randomized groups to test Rosenberg et al. [20] Social network analysis of Levy et al. [21] Controlled trialAral of et enhanced al. [22] Review of results from 2 Zimmerman-Rogers et Elliott et al. [16] Audit of PN activity

S141 Table 1. (Continued).

Study population Exposure/ Outcome Reported Design analysis Subjective Citation Study design type/setting intervention measures ﬁndings quality/biases quality rating

Zenilman et al. [24] Geographic study of distance STD clinic pts; reported cases Study of distance between Distance between partners in GC partners are significantly Innovative design for examining Good between partners with GC of GC in an inner-city urban partners compared with a 286 dyadic relationships closer to each other com- the neighborhood or local social in core areas environment generated distance pared with randomly se- network characteristics of gon- lected addresses; W were orrhea infection in 2 core areas; median 547 m from partners supports the core theories of and M 339 m from partners transmission of disease Potterat et al. [10] Retrospective review of case- STD clinic pts Examination of conccurrency Ors associated with network Overall R p 0.55 (not enough Observational study that used Good finding results and reproductive number factors compared with num- to sustain transmission) but available data among contacts to persons bers of partners for likeli- was highest among persons with CT hood of being a CT with concurrent partners transmitter (enough to sustain); concurrency was most important single factor in determining a transmitter, stronger than simple number of partners Rothenberg et al. [25] Prospective study of applying Community-based population Used social network and eth- Network demonstration of con- 396 persons identified with cu- Use of routine PN data to con- Good social network techniques of people with and at risk nographic approaches to nected groups of active mulative prevalence of struct social network character- to endemic syphilis for syphilis identify persons beyond transmitters; contact indices 12.6% for syphilis; network istics; problems of non- transmission simple sex partnership approaches can account for identification diminished by у30% of found cases; sev- large “net” of identification of eral case studies of effec- persons at risk tiveness of indirect network methods Laumann et al. [26]a Data from National Health and General population Survey sought measures that Complex mathematical con- Among blacks, assortative mix- Complex study; numerous as- Good Social Life Survey: probabil- might indicate network asso- struct to assess relationship ing with regard to ethnicity sumptions required to arrive at ity sample of US citizens ciations and probability of of sexual network to prior and dissassortative mixing conclusions having had an STD (by STD infection with regard to level of sex- history) ual activity may account for higher prevalence Howell et al. [27]a Cost-effectiveness model for Hypothetical Compared (1) dx and rx of fe- Cases of PID prevented and (1) prevented more cases and Assumptions about role of M Good CT infection male sex partners with M cost for each strategy was considerably more cost- with long-term infection may with CT; (2) preventing rein- saving not hold fection in women through dx and rx of male sex partners Rahman et al. [28]a Cost-effectiveness of PN for Hypothetical Assumed given level of effec- Cost/year of life gained Estimated $4930/year of life Numerous assumptions about ef- Fair HIV tiveness of counseling for gained through application fectiveness of the PN safer sex practices; trans- of PN intervention lated to prevented cases Ghani et al. [29]a Monte Carlo simulation to Hypothetical “True” network was then ex- Degree of bias in the samples All 3 produce biases, but con- Numerous assumptions and Good generate true networks plored to determine what produced by each method tact tracing approach may simplifications portion would be “discov- be adequate in several ered” through 3 PN sam- cases pling methods (reports by participants, snowball sam- plings, contact tracing)

NOTE. anon., anonymous; CT, Chlamydia trachomatis; dx, diagnosis; GC, gonorrhea; GU, genitourinary; IDU, injection drug user; M, men; OR, odds ratio; pts, patients; Rx, treatment; STD, sexually transmitted disease; W, women.

a Article models some aspect of PN. Downloaded from https://academic.oup.com/cid/article/35/Supplement_2/S138/314336 by guest on 01 October 2021 October 01 on guest by https://academic.oup.com/cid/article/35/Supplement_2/S138/314336 from Downloaded Table 2. Elements of a coordinated approach to investigating the network characteristics of sexually transmitted disease (STD) transmission.

Type of study Examples Correlation of network structure with disease occurrence Selecting a spectrum of communities with varying disease prevalence and along the continuum of prevalence of major STDs performing network ascertainment studies among persons at risk for specific diseases Analysis of network factors associated with outbreak Use of a network-informed approach that broadens the targets for traditional situations for the major STDs partner notification activity to observe the added value the approach provides in controlling disease transmission; provide long-term follow-up to determine effects on endemicity Assessment of the relationship and relative importance Longitudinal studies that provide joint information on personal characteristics, Downloaded from https://academic.oup.com/cid/article/35/Supplement_2/S138/314336 by guest on 01 October 2021 of personal behavioral characteristics and the network behaviors, and network properties to use in multivariate approaches that situations in which they are found assess the joint effect of these multilevel attributes on outcomes such as disease transmission or acquisition Use of network properties for case-finding and targeting Use of specific questions of groups at risk (e.g., ethnographic inquiry into of investigational resources the general nature of the social network) as a mechanism for prioritizing outreach and screening and evaluating the impact of such approaches Use of an individual’s network characteristics for case- Use of specific questions of persons at risk (e.g., perception of risk in their finding and targeting of investigational resources associates) as a mechanism for prioritizing outreach and screening and evaluating the impact of such approaches Attempting a larger scale demonstration of the efficacy Establishing several high-prevalence areas that undertake a coordinated of the network-informed approach approach to targeting resources to small, clustered groups within the area of concern

were asked to identify others they knew who might be practicing In a follow-up to that outbreak investigation, Rothenberg et unsafe sex. Of 30 persons identified, 17 were HIV-positive and al. [25] conducted a 6-month demonstration project in a high- 9 had been previously unaware of their infection. In a second morbidity area in inner-city Atlanta and demonstrated that the focus group, persons were asked to identify persons they use of the larger social network perspective can be of consid- thought might be HIV-positive. Of 15 such persons identified, erable value in identifying new cases and in securing follow- 11 were HIV-positive and 8 had been previously unaware of up with typically difficult-to-reach people. In all, 48 cases of their infection. Although the communication provides little syphilis were identified in a group of 396 people (a 6-month information about the actual persons involved, the use of such cumulative incidence of 12.6%), 275 of whom could be con- techniques for case finding and targeting services deserves fur- nected to each other in a single component. They estimated ther exploration, because it uses social (as well as sexual or that ∼30% of the cases found during this period could be drug-using) contacts who do not bear the traditional PN re- attributed to network connections (friends, associates, or eth- lationships to the reporting patient. nographically connected persons) obtained outside the usual Epidemic and endemic transmission. A similar nontradi- realm of PN. For example, 8 cases were connected directly to tional path was used by Rothenberg et al. [18], who investigated a single person through the process of network ascertainment, an outbreak of syphilis among teenage girls and boys in a although none of them had been identified as a partner by that suburban community. They found that interviewing important person. The study did not, however, provide information on persons—not necessarily sex contacts—identified through net- the longer term impact of the process on the interruption of work connections or other ethnographic means was a valuable disease transmission. In a study of syphilis transmission in adjunct to case finding. In fact, interviewing persons with or Louisiana, Rosenberg et al. [20] indicated the importance of without syphilis in such a network had the same yield of positive central persons in the network, whom they felt were “core contacts. In addition, they demonstrated that traditional no- transmitters.” Their diagram of network activity was consistent tions of source and spread cannot be used in a network in with low-level endemic transmission. Using network ascertain- which cases have overlapping contact with multiple other cases. ment, Stoner et al. [45] demonstrated clear differences in the Finally, they showed that the prevention of cases could be better networks of persons infected with Nisseria gonorrheae or Chla- documented through network connections that showed mul- mydia trachomatis. Incarceration, crack use, and a continuing tiple exposure to syphilis in persons who were epidemiologically drug problem were far more common in the networks of per- treated before onset of clinical or serologic evidence of disease. sons with gonorrhea.

Transformation of Partner Notification • CID 2002:35 (Suppl 2) • S143 Mixing matrices. Continuing the theme of the use of net- than was the actual number of partners, thus providing em- work-related concepts, Aral et al. [22] demonstrated that per- pirical evidence for the theoretical and model-based importance sons with gonorrhea and chlamydia have differing mixing ma- of such structure. trices (the frequency with which groups with given In keeping with the recent appearance of network-motivated characteristics have contact with each other). In particular, they PN studies, those who display greater enthusiasm for the pro- showed that the differences in mixing patterns between the 2 cess do so from a network perspective [50–53]. These authors infections centered on social characteristics (ethnicity, age, and have stressed the larger perspective that network-informed PN sex) rather than on risk behavior, such as number of partners. provides, the insights into disease transmission, and the po- They demonstrated as well the importance of links (bridges) tential for a variety of newer interventions that may be network- between high- and low-prevalence populations. Such infor- based. It is important to recognize, however, that these studies mation is of importance in identifying groups at greater risk represent some early efforts to inject network concepts into the Downloaded from https://academic.oup.com/cid/article/35/Supplement_2/S138/314336 by guest on 01 October 2021 for specific infections on the basis of their network associations. traditional PN practices. Consideration of mixing patterns of Using a different approach, Laumann and Youm [26] analyzed persons at risk, of the geographic contiguity of current and data from the National Health and Social Life Survey to ex- potential sex partners, and of notions of social structure all amine mixing patterns and self-reported STDs. They concluded appear to add to an understanding of the dynamics of disease that the general higher prevalence of some STDs among the transmission. It is clear that a more coherent and concerted black population might have a network explanation: a pro- approach is required to investigate the value of PN in the net- pensity for assortative mixing (like with like) with regard to work context and to establish the basis for further intervention ethnicity and for disassorative mixing with regard to level of activity (table 2). The empirical data on which such under- sexual activity (highly active with less highly active). standing is based are derived directly from the PN approach Geographic clustering. Another form of network associa- that has been part of STD control for many years. Such analysis tion—spatial proximity—was highlighted by Zenilman et al. requires the addition of information about networks—social [24], who demonstrated remarkable geographic proximity of partners, drug-using partners, acquaintances, ethnographically dyads with gonorrhea, confirming the neighborhood nature of connected individuals, and possibly even family members—and disease transmission and the geographically cohesive charac- the use of network analytic tools to provide the broader context teristics of core groups. These observations using quantitative for assessing the intensity of relationships and the propensity measurement of distance confirmed earlier assertions, based on for transmission. more traditional PN analysis, that gonorrhea was a neighbor- These additions are obviously important in a research context hood disease [46]. The availability of simpler geographic in- but are just as important for ongoing programs. Ultimately, formation systems now provides a method for the more intense changes in the modus operandi for disease-control efforts that investigation of this aspect of network associations as well as use PN rest with their acceptance in the field, and field attempts other factors associated with the conduct of network studies at incorporation are critical for such acceptance. These initial [47]. Such observations may be of considerable value in fo- studies would appear to warrant a broad-based inclusion of cusing control efforts on specific locations. network concepts into programmatic activities, with careful Network structure. In an article on the case-finding results monitoring and analysis of the impact they have both on the from an intensive chlamydia control effort, Zimmerman-Rog- traditional indices of PN as well as the larger effect on disease ers et al. [23] demonstrated that the usual interview periods, transmission. as promulgated by the CDC, will reveal most of the contacts but miss a potentially important group, men with long-term asymptomatic infection, who might be of considerable impor- References tance. They point out that traditional case-finding intervals may 1. Rothenberg RB, Potterat JJ. Partner notification of sexually transmitted ignore the network implications of such persons in maintaining diseases and HIV infection. 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