Hepatitis A: report of a common-source outbreak with recovery of a possible etiologic agent. I. Epidemiologic studies

From the end of October to the end of December 1973, an epidemic of hepatitis A affected 40 students at a state university, 11 employees of two restaurants, and 11 other residents in a southwestern metropolitan community. Two distinct epidemic waves of illness occurred, and investigation implicated two local restaurants as sources of infection, one for each epidemic wave. An index patient who prepared food was identified at each restaurant, and the two restaurants were linked by the fact that the index patient who worked at the second restaurant had patronized the first restaurant. Foods implicated as vehicles of transmission included 'guacamole,' green salad, spaghetti, and hamburger. The findings represent a rare example of a 'double' common-source outbreak with two distinct epidemic waves related to two separate eating establishments.