An outbreak of salmonellosis propagated by person-to-person transmission on an Indian reservation.

Between December 21, 1969, and April 14, 1970, 44 symptomatic cases of Salmonella typhimurium gastroenteritis occurred among the approximately 2500 Sioux Indians of the Lake Traverse Reservation in South Dakota. Twenty-five cases were confirmed by positive stool culture. All 19 cases not confirmed by culture had diarrhea and were epidemiologically associated with the culture-proven cases. Fourteen of these were discovered during the course of the investigation and had not been cultured previously. Twelve cases were hospital-acquired and 32 community acquired. Both the nosocomial and community-acquired infections occurred randomly during the 17-week span of the epidemic. Despite extensive investigation, no common exposure was discovered. The hospital-acquired infections all occurred in patients who shared a room or nursing personnel with patients who had active disease, or were born of a woman with active disease at the time of parturition. Twenty-nine of the 32 community acquired cases were linked to each other by person-to-person contact. This epidemic is the first documented outbreak of non-institutional salmonellosis propagated by person-to-person transmission.