A food-borne outbreak of gastroenteritis caused by norovirus GII in a university located in Xiamen City, China

Summary Objectives We investigated a diarrhea outbreak that occurred at a university in China to identify the etiological agent of the outbreak, source of infection, mode of transmission, and risk factors. Methods In this case–control study, we compared the food sources and examined the food and water items consumed between the probable and confirmed cases and the asymptomatic control students, who were selected randomly and frequency-matched by class and age at a ratio of 1:2. Results Out of 7141 students (excluding teachers), 87 (1.2%) developed an illness. Thirty-three of 44 (75%) cases and 11 of 88 (13%) control students had consumed bread products supplied by an unlicensed small bakery (odds ratio 21, 95% confidence interval 8–60). Norovirus GII was detected in seven patients and in a food handler at the bread workshop and his 8-month-old son. Conclusions The outbreak of gastroenteritis was caused mainly by bread products contaminated with norovirus GII. A food handler with an asymptomatic norovirus GII infection was the possible source of infection.