A large outbreak of gastroenteritis caused by diarrheal toxin-producing Bacillus cereus

An outbreak of diarrhea occurred after a university field day. Of 643 attendees who returned mailed questionnaires, 139 (22%) reported illness. Persons who ate barbecued pork, which was unrefrigerated for 18 h after cooking, were five times more likely to become ill than those who did not eat pork (26% vs. 5%; relative risk, 5.4; 95% confidence interval, 1.4-20.9). A leftover pork sample grew a Bacillus cereus isolate, > 10(5) cfu/g, that produced diarrheal toxin. Thirty-four percent of ill persons noted onset of illness outside the 6- to 24-h incubation period traditionally ascribed to B. cereus-mediated diarrhea, and an unusually high percentage (23%) noted fever. B. cereus may cause a wider spectrum of disease than previously described.