A WATERBORNE EPIDEMIC OF GASTROENTERITIS WITH SECONDARY PERSON-TO-PERSON SPREAD

A large epidemic of gastroenteritis occurred among persons who had visited a Pennsylvania State park between June 5 and June 8,1966. A total of 454 cases with either vomiting or diarrhea were identified, and it seems likely that several thousand illnesses actually occurred. The average incubation period was 29 hours with an attack rate of 69%. Epidemiologic and laboratory evidence implicated the water supply of the park as the source of the outbreak. Secondary cases of gastroenteritis occurred in household contacts who had not been exposed to the park water supply; the average incubation period of the secondary cases was 63 hours and the secondary attack rate was 44%. The high secondary attack rate among household contacts suggested the presence of an infectious agent. No recognized bacterial pathogens or viral organisms could consistently be isolated from the stools of 171 patients or from the drinking water. The epidemic was not followed by the occurrence of hepatitis.