Epidemiology of common-source outbreaks of shigellosis in the United States, 1961-1975.

In 1961-1975, there were 72 foodborne and 38 waterborne outbreaks of shigellosis reported in the United States. Foodborne outbreaks were most often caused by salads with contamination attributed to poor hygiene of a food handler. Waterborne outbreaks most often involved semipublic water systems, and were usually the result of inadequate chlorination of water contaminated by human feces. In 110 common-source outbreaks, 16,541 persons were ill. The attack rate for both food- and waterborne shigellosis was 47%, and the case-fatality ratio was 0.1% in foodborne outbreaks and 0.2% in waterborne outbreaks.