On 4 September 2018, a boarding school in the Shunyi District of Beijing, China reported an outbreak of acute gastroenteritis. At least 209 affected students developed the symptoms of diarrhea and vomiting. Investigations were conducted to identify the agent and source of this outbreak, and to implement controls to prevent further transmission.
A retrospective cohort study was conducted among the school students and staff in order to test hypothesis that food served at the school canteen. We collected information on demographics, refectory records at the canteen and contact to ill persons or vomit, using a uniform epidemiological questionnaire. Risk ratios (RR) and 95% conﬁdence intervals (CI) were calculated. Stool specimens of cases and canteen employees, food served, water, and environmental swabs were investigated by laboratory analysis.
We identiﬁed 209 cases(including 28 laboratory-confirmed cases) that occurred from August 29 to September 10. All cases were students, and the median age was 20 years, 52% were male. The outbreak lasted for 13 days, and peaked on September 5. Consumption of Drinks window and Rice flour window on 1 September(RR: 3.4, 95% CI: 1.5-7.8, and RR: 7.6, 95% CI: 2.8-20.2), Rice flour window and Fish meal window on 2 September(RR: 4.0, 95% CI: 1.2-13.6, and RR: 4.6, 95% CI: 1.7-12.5), Moslem meal window on 4 September(RR: 2.7, 95%CI: 1.3-5.4), Barbeque window on 5 September(RR: 3.0, 95%CI: 1.2-7.0) were independently associated with increased risk of disease within the following 2 days. Rectal swabs or stool samples from twenty-five cases and ten canteen employees were positive for norovirus GI.6. Five cases were positive for Bacillus cereus, among them, two stool samples were detected by a mixed infection of Norovirus and Bacillus cereus. Four retained food specimens were positive for Bacillus cereus, and environmental samples were negative for any viruses or bacteria.
Our investigation indicated that consumption of high-risk windows was the source of this outbreak. The high rate of infection of both pathogens was exacerbated by unhygienic manipulation and Inappropriate hygiene practices in canteen employees.