Infectious hepatitis in California; a community-wide epidemic.

In an epidemic of infectious hepatitis in a rural California community during 1961, 514 cases were reported among 8,166 residents. A sample of the 396 cases reported up to 1 September was studied, and only about a third of these cases could be confirmed in retrospect. A community survey indicated that the attack rate for the first eight and a half months of 1961 was slightly over 3 per cent. Unusual epidemiologic features of what was thought to be a contact epidemic included a summer peak, a preponderance of young and middle-aged adults, a relative sparing of lower socioeconomic groups and mildness of the illness with jaundice appearing in a minority of cases. Secondary cases were rarely observed within the expected 10- to 50-day incubation period.