Another reporting source for apparent clusters of both infectious and noninfectious disease is patients or other members of the community. For example, an individual may call the health department and report that she and some friends came down with severe gastroenteritis after attending a banquet a night or two earlier. Similarly, a local citizen may call about several cases of cancer diagnosed among his neighbors and express concern that these are more than coincidental. Most health departments have routine procedures for handling calls from the public regarding potential communicable disease outbreaks, and some states have guidelines for how to respond to noninfectious disease cluster reports.7-9
Deciding whether to investigate a possible outbreak
Different health departments respond to these reports in different ways. The decisions regarding whether and how extensively to investigate a potential outbreak depend on a variety of factors. These usually include some factors related to the health problem, some related to the health department, and some related to external concerns. Factors related to the problem itself include the severity of the illness, the number of cases, the source, mode or ease of transmission, and the availability of prevention and control measures. Most local health departments are more likely to investigate an apparent outbreak when the number of affected (or exposed) persons is large, when the disease is severe (serious illness with high risk of hospitalization, complications, or death), when effective control measures exist, and when the outbreak has the potential to affect others unless prompt control measures are taken. For example, a single case of gastroenteritis is unlikely to prompt a field investigation, but a cluster of cases may. On the other hand, even a single case of botulism is likely to be investigated immediately to identify and eliminate the source, because it is both potentially fatal and preventable, and the source can usually be identified. At the state or national level, the unusual presentation of disease may spur an investigation. Occurrence of a new or rare disease or a change in the pattern of disease in an area is more likely to prompt an investigation than occurrence of a common disease with well-established transmission patterns and control measures