Outbreak of Salmonella Braenderup infection originating in boxed lunches in Japan in 2008

There have been only 2 reports of a large-scale foodborne outbreak arising from Salmonella enterica serotype Braenderup infection worldwide. On August 9, 2008, an outbreak originating in boxed lunches occurred in Okayama, Japan. We conducted a cohort study of 786 people who received boxed lunches from a particular catering company and collected 644 questionnaires (response rate: 82%). Cases were defined as those presenting with diarrhea (> 4 times in 24 h) or fever (> 38°C) between 12 am on August 8 and 12 am on August 14. We identified 176 cases (women/men: 39/137); younger children (aged < 10 years) appeared to more frequently suffer severe symptoms. Three food items were significantly associated with higher risk of illness; tamagotoji (soft egg with mixed vegetables and meat) (relative risk (RR): 11.74, 95% confidence interval (CI): 2.98-46.24), pork cooked in soy sauce (RR: 3.17, 95% CI: 1.24-8.10), and vinegared food (RR: 4.13, 95% CI: 1.6010.63). Among them, only the RR of tamagotoji was higher when we employed a stricter case definition. Salmonella Braenderup was isolated from 5 of 9 sampled cases and 6 food handlers. It is likely that unpasteurized liquid eggs contaminated by Salmonella Braenderup and used in tamagotoji caused this outbreak.