Table 3.

Steps in the Investigation of an Epidemic

1. Determine that an epidemic or outbreak actually exists by comparing with previous data on the disease

2. Establish an etiologic diagnosis if possible; if not, define the condition epidemiologically and clinically. Collect materials for isolation and serological test, and data from sick and well-exposed persons

3. Investigate the extent of the outbreak by a quick survey of hospitals, physicians, and other sources and its basic epidemiological characteristics in terms of time, place, person, probable method of spread, and the spectrum of clinical illness. Prepare a spot map of cases and an epidemic curve. Call in outside help if needed

4. Formulate a working hypothesis of the source and manner of spread as a basis for further study

5. Test the hypothesis by determining infection and illness rates in persons exposed or not exposed to putative source(s) of infection by questionnaire, interview, and laboratory tests. Try to isolate the agent from the putative source(s)

6. Extend epidemiological and laboratory studies to other possible cases or to persons exposed but not ill

7. Analyze the data and consider possible interpretations

8. On the basis of the analysis, initiate both short- and long-term control measures

9. Report the outbreak to appropriate public health officials

10. Inform physicians, other health officials, and the public of the nature of the outbreak and the ways to control it