Introduction: Non-typhoidal Salmonellae are important causes of bacterial food-borne infection, especially in institutional settings. An outbreak of gastrointestinal infection occurred in a military camp in January 2007, and an epidemiological outbreak investigation was conducted. Materials and Methods: A survey was conducted on soldiers in the camp on their clinical symptoms, and recent meals consumed. After determining the affected meal, a subsequent survey was conducted on those who had eaten the meal. A case-control study was then performed to determine the outbreak’s likely food source. Laboratory tests were also conducted to determine the bacteriological cause. Results: Of the 94 responders, 55 (58.5%) met our case definition of gastrointestinal illness. The dinner on 9 January was the most likely affected meal, with the onset of symptoms occurring within 6 to 36 hours. The mashed potato was the most likely food source with an attack rate of 80.7% for those who consumed it versus 32.7% for those who did not (P <0.01). From the multivariate analysis, the mashed potato remained the only food item independently and significantly associated with infection, with a relative risk of infection 9.49 times those who did not consume it (95% CI, 2.73-32.97). Salmonella group E was cultured from 4 individuals. Although no specific contamination was identified, the mashed potato was stored for more than 5 hours before the last serving. Conclusion: Risk during preparation of large quantities of food should be identified a priori, and measures taken to reduce them, to prevent outbreaks.
Bacterial food-borne infections are common, especially where hygiene has not been optimal. Non-typhoidal Salmonellae are important causes of bacterial food borne infection worldwide. There are an estimated 1.4 million cases of Salmonella infections annually in the United States,1,2 while non-typhoidal Salmonellae has been found to be responsible for 56.1% of acute admissions for diarrhoea among children in one hospital in Thailand.3 In Singapore, 345 and 296 cases of non-typhoidal laboratory confirmed salmonellosis were reported in 2004 and 2005 respectively.
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