Surveillance for Epidemics -- United States

Although state health departments document investigations of disease epidemics and outbreaks, there is no national system for surveillance of epidemics. In 1988, a 5-month pilot project to assess the feasibility and utility of a standard computerized surveillance system for epidemics was conducted by state epidemiology programs in Maryland, New York, Oklahoma, and Washington, and by the Epidemiology Program Office, CDC.

From June through October, 1988, the four participating state epidemiology offices used a uniform data collection system to record reported epidemics investigated by their staffs or by other agencies in their states. For this project, an epidemic or outbreak was defined as: "A recent or sudden excess of cases of a specific disease or clinical syndrome. For a foodborne outbreak, ngreater than or equal to 2; for other outbreaks, ngreater than or equal to 3." Although designed principally to collect information on epidemics, the system also allowed for reporting other epidemiologically important events, including individual cases of rare diseases (e.g., botulism and human rabies) and toxic exposures without documented subsequent illness (e.g., a hazardous material spill during transport).

During the 5 months, 116 events were reported. Maryland and Oklahoma, which already maintained systems of epidemic reporting similar to the pilot system, accounted for 39 (34%) and 33 (28%) reports, respectively. Washington and New York, with pre-existing systems considerably different from the pilot system, accounted for 25 (22%) and 19 (16%), respectively. The number of reported events per 100,000 population was 1.0 in Oklahoma, 0.8 in Maryland, 0.5 in Washington, and 0.1 in New York (1). Local health departments originated reports for 69 (59%) events. The timeliness of reporting was measured as the interval between date of onset for the index case and date of report to the state health department. Dates were recorded for 106 events; of these, the reporting interval was less than or equal to 1 week for 64 (60%) and less than or equal to 2 weeks for 78 (74%).

Seventy-nine (68%) of the events were epidemics or outbreaks; of these, 77 (97%) were caused by communicable diseases. The majority of these were relatively small outbreaks--51 (66%) involved less than 10 persons. The largest, an outbreak of viral gastroenteritis, involved 64 persons at a nursing home in Oklahoma. The most frequently reported locations associated with outbreaks were commercial food establishments (25%), nursing homes or other long-term care facilities (15%), and the general community (10%). For the 39 (51%) infectious disease outbreaks in which an etiologic agent was reported, the most common agents were Salmonella (26%) and hepatitis A virus (23%). Reported by: C Groves, E Israel, MD, State Epidemiologist, Maryland State Dept of Health and Mental Hygiene. S Kondracki, DL Morse, MD, State Epidemiologist, New York State Dept of Health. P Archer, S McNabb, GR Istre, MD, State Epidemiologist, Oklahoma State Dept of Health. M Chadden, JM Kobayashi, MD, State Epidemiologist, Washington State Dept of Social and Health Svcs. Council of State and Territorial Epidemiologists. Div of Field Svcs, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: The current national system of notifiable disease reporting (data reported weekly in MMWR Tables I, II, and III (pages 688-691)) provides surveillance data on a wide range of diseases, many of which can cause epidemics. The 121-city mortality surveillance system (data reported weekly in MMWR Table IV (page 692)) is used to assist in identifying epidemic influenza (2). However, except for a limited set of problems (e.g., waterborne outbreaks (3)), no uniform national system of surveillance exists for epidemics. Consequently, neither CDC nor state epidemiology programs have access to uniform, comparable surveillance data for monitoring temporal and geographic trends of epidemics or for providing national estimates of the frequency of epidemics.

Although most states maintain written records for epidemic surveillance, many do not routinely computerize these data. Increased use of automation might facilitate analysis and evaluation of such data, as well as expedite intervention/prevention efforts. Systematic surveillance of epidemics could be used to improve disease prevention efforts at both state and national levels. For example, epidemic surveillance data could be used to evaluate and improve regulations and standards of public health practice related to child-care licensing, restaurant inspections, and environmental hazard control. This approach might permit comparison of the effectiveness of differing standards in different local or state jurisdictions, measurement of the impact of changes in standards over time, and early detection of changing patterns in the transmission of notifiable diseases, such as the recent increased incidence of hepatitis A transmission among drug abusers (4).

This pilot project demonstrated both the feasibility and constraints associated with development of a standard system for surveillance of epidemics. Each of the par ticipating states recognized the utility of the data generated by the project. However, two of the states noted that a permanent system would require substantial revision of their current procedures for collecting and reporting surveillance data. The wide variability of the ratio of reported events to population size probably reflects differences in data included in this system rather than in occurrence of epidemics (e.g., most reports of small foodborne disease outbreaks in New York come directly to the State Bureau of Community Sanitation and Food Protection rather than to the office of the state epidemiologist).

At its annual meeting in May 1989, the Council of State and Territorial Epidemiologists unanimously passed a resolution supportingthe concept of state-based epidemic surveillance and endorsed CDC efforts to develop a uniform system that permits comparable information to be collected, analyzed, and shared among the states.

References

1. Bureau of the Census. Annual estimates of the resident population of states: April 1, 1980 to July 1, 1988. Washington, DC: US Department of Commerce, Bureau of the Census, 1989; release no. CB89-47.

2. Choi K, Thacker SB. An evaluation of influenza mortality surveillance, 1962-1979. II. Percentage of pneumonia and influenza deaths as an indicator of influenza activity. Am J Epidemiol 1981;113:227-35.

3. CDC. Water-related disease outbreaks, 1985. In: CDC surveillance summaries, June 1988. MMWR 1988;37(no. SS-2):15-24.

4. Harkess JR, Gildon B, Istre GR. Outbreaks of hepatitis A among illicit drug users, Oklahoma, 1984-87. Am J Public Health 1989;79:463-6.

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