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Bacillus cereus Food Poisoning Outbreak in a Hospital, Associated with Harees, Muscat, Oman, February 1999


On February 19, 1999, inpatients, their attendants and visitors at Khoula Hospital, Muscat, Oman, started to complain of diarrhea and abdominal pain, after eating food prepared at the hospital restaurant. The investigation started to identify the source of the outbreak and recommend control measures for prevention of a similar situation in the future.


A case was defined as any person who ate food prepared at Khoula Hospital on Friday, February 19, 1999, and developed diarrhea and abdominal pain with or without vomiting between February 19 and 21, 1999. All the inpatients and their attendants and visitors were interviewed and asked about food history and symptoms through a questionnaire. Specimens from curd (yoghurt), prepared in the restaurant and served at lunch on Friday, February 19, 1999, and the raw material of Harees (ground wheat), served at dinner on the same day were taken for culture. In a case-control study to implicate food items, the odds ratio (OR) and 95% confidence interval (CI) were calculated.


A total of 80 persons were interviewed, 40 cases and 40 controls. Eighty percent of the cases complained of diarrhea and abdominal pain and the other 20% complained of diarrhea only. The dinner on February 19, 1999, was the implicated meal and the illness was associated with Harees (OR 21 and P value <0.05). The illness developed between 4 and 29 hours (median 7 hours) after eating. Bacillus cereus was isolated from the Harees specimen with a count of >10 per gram and the specimen of curd was sterile. The dinner was prepared at 4:00 p.m. and served at 6:30 p.m.


The source of the organism was the raw material of Harees and the time- temperature abuse was the principle factor contributing to the outbreak. It was recommended that raw materials of food items should not be stored in large quantities in open containers and cooked food should be kept hot, at a temperature of at least 60°C.