Epidemiologic Surveillance

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Epidemiologic surveillance is the ongoing systematic collection, recording, analysis, interpretation, and dissemination of data reflecting the current health status of a community or population. The scope of epidemiologic surveillance has evolved from an initial focus on infectious disease monitoring and intervention to a more inclusive scope that includes chronic diseases, injuries, environmental exposures, and social factors that influence health status. Surveillance is based on both passive and active data collection processes. When a clinician or laboratory encounters a patient or sample indicating the presence of certain conditions or pathogens, there is a legal obligation to report the case to local public health officials. The result is a passive monitoring of the levels of the disease in the community. As of 1998, there were fifty-two infectious diseases that were classified "notifiable" in the United States at the national level. Active surveillance, on the other hand, is commonly referred to as "case finding." This occurs when the data necessary to monitor levels of a medical or social condition is sought out actively. This is accomplished through a variety of means, ranging from clinical record reviews to community surveys.

Epidemics have traditionally been defined by the occurrence of more cases of disease than expected in a given area or among a specific group of people over a particular period of time. However, the definition of an epidemic has evolved as the scope of surveillance has evolved. Such issues as domestic or school violence, unemployment, and crime have, from time to time, fit the definition and have been described as epidemics. Issues like these are used, in conjunction with more medically oriented issues, to assess the health status of a community or population.

Epidemiologic surveillance uses a wide variety of data sources, depending upon the circumstance under investigation. For communicable diseases, local and state health departments typically rely on passive reporting. Other sources of data for epidemic surveillance include birth and death certificates; sentinel surveillance sites (i.e., the use of community-based health or occupational sites to monitor for specific health events); cancer, birth defects, and other registries; health interview surveys; and hospital or ambulatory care data collection systems.

Merely monitoring the current status of disease prevalence, health indicators, or social markers does not protect the health of a community. Careful monitoring, however, creates a baseline measurement of threats to the public's health. It is this established baseline that enables public health workers to notice when an anomaly occurs. A sharp increase in the number of cases of a disease will instigate further investigation, intervention, and prevention measures. Surveillance of an epidemic requires a very specific definition of what constitutes a case that can be counted. The number of suspected cases, probable cases, and confirmed cases of a disease are actively sought and monitored. The number of cases, and the relationship between cases, is used during an outbreak investigation in an attempt to identify causes and those at risk, and to implement an intervention.

Marguerite A. Erme

Thomas C. Quade

(see also: Chronic Illness; Communicable Disease Control; Community Health; Epidemics; Epidemiology; Incidence and Prevalence; National Health Surveys; Notifiable Diseases; Registries; Surveillance; Surveys )


Friis, R., and Sellers, T. (1996). Epidemiology for Public Health Practice. Gaithersburg, MD: Aspen Publishers, Inc.

Gregg, M. (1996). Field Epidemiology. New York: Oxford University Press.

Teutsch, S., and Churchill, R. (1994). Principles and Practice of Public Health Surveillance. New York: Oxford University Press.