Outbreak of acute gastroenteritis attributable to Escherichia coli serotype O104:H21--Helena, Montana, 1994.

During February-March, 1994, four persons in Helena, Montana (1995 population: 24,569), developed bloody diarrhea and severe abdominal cramps. Stool cultures for Salmonella, Shigella, Campylobacter, and Escherichia coli O157:H7 were negative; however, sorbitol-negative E. coli colonies were identified in stools from all four patients. Isolates from three patients were identified at CDC as a rare serotype--E. coli O104:H21 that produced Shiga-like toxin II. This report summarizes the epidemiologic and laboratory investigations of this outbreak by the Lewis and Clark County Department of Health and Environmental Sciences, the Montana Department of Health and Environmental Sciences (MDHES), and CDC.