Infectious Disease Surveillance Jillian Murray and Adam L Cohen, World Health Organization, Geneva, Switzerland Ó 2017 Elsevier Inc. All rights reserved. World Health Organization retains copyright in the manuscript and provides Elsevier the permission to publish the manuscript as a chapter in this book. Goals of Infectious Disease Surveillance into the population. The Zika outbreak in South America in 2015–16 demonstrates how rapidly a known pathogen in Infectious disease surveillance is an important epidemiolog- a naïve population can spread. ical tool to monitor the health of a population. The goals of infectious disease surveillance are threefold: (1) to describe Infectious Disease Surveillance Methods the current burden and epidemiology of disease, (2) to monitor trends, and (3) to identify outbreaks and new path- Infectious disease surveillance can have different approaches ogens. First, describing the burden and epidemiology based on the epidemiology and clinical presentation of the (including seasonality, age distribution, age groups, etc.) of disease and the goals of surveillance. We will discuss some disease is critical for demonstrating the need and advocating distinctions between infectious disease surveillance methods for interventions, such as vaccination and mass drug adminis- and give examples below. tration. Surveillance is also used to detect antimicrobial resis- tance in certain pathogens (for example, fluoroquinolone Active versus Passive Surveillance resistance in gonorrhea) and the circulating strains of disease, which helps target vaccine interventions (for example, annual In passive surveillance systems, medical professionals in the influenza vaccine composition). community and at health facilities report cases to the public Second, infectious disease surveillance is used to monitor health agency, which conducts data management and analysis disease trends, such as the impact of interventions like vacci- once the data are received. Public health staff do not engage in nation. Disease trends do not only mean the number of identifying cases but rather assess data completeness and reli- cases, but also the etiology of cases. For example, after pneu- ability of the reported cases. In contrast, active surveillance mococcal conjugate vaccine introduction, the distribution of requires public health staff to engage actively in the system serotypes causing disease should be surveyed for serotype and take action in order to receive reports of disease cases. replacement, when the incidence of disease caused by sero- This may involve calling or visiting health facilities to encourage types not covered in the vaccine may increase following the follow-up or having staff review medical records to identify cases decline in disease due to vaccine serotypes from vaccination. meeting prescribed case definitions. Active surveillance aims to Information garnered from vaccine effectiveness studies can detect every case, and passive surveillance likely misses cases be coupled with burden and cost information to describe due to the reporting structure. Although active surveillance is the cost-effectiveness of interventions. more comprehensive, it requires significant human and financial Surveillance also monitors the control, elimination, and resources, so passive surveillance is often implemented. eradication of diseases. Disease control refers to reducing the Notifiable disease surveillance is an example of passive incidence of disease to a desired level (which will vary depend- surveillance. Notifiable diseases are classified as such because ing on the disease) and includes diseases such as malaria they are of public health importance: they can be a severe risk (Dowdle, 1999). Disease elimination is defined as zero disease to human health, outbreak prone, considered to be an emerging inadefined geographic area as a result of control measures. Prog- or reemerging disease, or have a timely intervention available ress toward disease elimination requires control measures to for control of the disease. Countries mandate which diseases stay in effect. Disease eradication is defined as zero disease glob- are notifiable, many of which are infectious diseases. Globally, ally as a result of control measures, which are no longer required. the WHO, as described in the International Health Regulations, Smallpox is the only human disease and rinderpest is the only defines what is notifiable by every country to WHO, such as animal disease that have been eradicated from the world, but MERS-CoV (Middle East respiratory syndrome coronavirus) efforts are underway to eradicate polio and dracunculiasis. and Ebola. Nationally notifiable diseases depend on the Finally, a key aspect of infectious disease surveillance is the country. In the United States, the Centers for Disease Control cycle of detecting, responding to, and preventing outbreaks. and Prevention (CDC) and the Council of State and Ongoing surveillance for an outbreak- and epidemic-prone Territorial Epidemiologists compile a list of diseases that have disease can facilitate early detection of an outbreak, allowing mandated reporting to the CDC. These include foodborne a more rapid response and therefore mitigation of the and sexually transmitted infections, other infectious diseases outbreak. Epidemic meningococcal disease in the meningitis such as dengue, malaria, and HIV, and noncommunicable belt in Africa requires ongoing surveillance to identify diseases such as cancer. The list is updated every year. On 21 outbreaks in the region. Cholera surveillance is maintained January 2016, the list was amended to include Zika virus globally to detect outbreaks and requires mandatory reporting disease after an outbreak in South America resulted in cases to the World Health Organization (WHO). Emerging and ree- being imported into the United States. merging diseases also pose a big risk to public health. These Although not commonly used for surveillance purposes, diseases include both unknown pathogens that appear for the administrative data or vital statistics are another example first time in a population as well as known pathogens that of routinely gathered data that can be used as passive surveil- increase in geographic spread or severity or are reintroduced lance. The International Classification of Diseases (ICD-10) 222 International Encyclopedia of Public Health, 2nd edition, Volume 4 http://dx.doi.org/10.1016/B978-0-12-803678-5.00517-8 Infectious Disease Surveillance 223 is used globally for the standard naming of diseases in hospi- are reported to the Ministry of Health and WHO. Data are talized patients. Administrative data such as hospital billing analyzed to look at trends of disease, including pre- and data using ICD codes can be used for syndromic surveillance, postintroduction of vaccine. Other diseases that have glob- such as for pneumonia, if it is available for ongoing moni- ally coordinated sentinel surveillance networks include rota- toring of disease. These data may provide information on virus, influenza, and congenital rubella syndrome. the clinical characteristics of patients across different regions Surveillance for some diseases can be a mixture of passive and hospitals. and active surveillance wherein passive surveillance is comple- Active surveillance can have many approaches, including mented by active surveillance to investigate outbreak signals country-wide (e.g., for polio, measles, and rubella) or detected through passive surveillance. For example, surveil- restricted to sentinel sites that capture cases within a demined lance for Ebola virus disease is ongoing throughout the year catchment population. For example, as of 2015, the WHO– as it is a notifiable disease for many countries and globally. coordinated Global Invasive Bacterial Vaccine–Preventable During an outbreak, active case finding in the community is Disease (IBVPD) Sentinel Site Surveillance Network is enacted to find symptomatic patients as well as contact tracing a system of more than 100 hospitals in more than 54 coun- to find those at risk for developing the disease. tries that conducts active surveillance for meningitis, pneu- monia, and sepsis (Figure 1). Within this network, staff are Identifying Cases in Medical Facilities and the Community engaged to work specifically on finding all cases meeting thecasedefinition at the sites. Cases are enrolled into surveil- Choosing where to conduct surveillance is based on a number lance after they have been admitted to the medical facility. of considerations: How severe is the disease and how does it A case report form, filled out by the dedicated staff member, present? How important is it to find every single case? How details their clinical symptoms. Laboratory testing is done at outbreak prone is the disease? Cases of infectious disease the hospital for initial diagnosis or at a national or regional can be identified at medical facilities (hospitals and outpa- reference laboratory to monitor for trends in culture tient clinics) or in the community. The location of individuals positivity and serotype/serogroup incidence. These data enrolled into surveillance can vary based on clinical Figure 1 Map of sentinel surveillance site locations in the World Health Organization (WHO) Global Invasive Bacterial Vaccine-Preventable (IB-VPD) network reporting data from 2013 to 2015. 224 Infectious Disease Surveillance presentation of disease and access to health care. More severe effectiveness of a vaccine or other preventive measures. Surveil- cases of disease can often be identified