A norovirus gastroenteritis outbreak in high school caused by contaminated barrelled water in Guangdong, China

  • Water or foodborne
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Background:
On 20th February, 2019, a total of 32 cases were reported of gastroenteritis by a school. An epidemiology investigation was conducted to determine the source, identify the risk factors, and propose control measures and preventive recommendations.

Methods:
The probable cases was defined as all teachers, students and related staffs in the school with the symptoms of diarrhea (≥three times/day accompanied by variation in stool properties) or vomiting from 12th to 22nd February, 2019.A confirmed norovirus case was a probable case and norovirus positive from a rectal swab RT-PCR. Cases were searched by reviewing the school’s records and medical records and interviewing health teachers, and controls were selected for asymptomatic one. We selected 49 cases and 56 controls, matched by class and sexy. A case-control study was used to explore the risk factors in drinking barreled water, dealing with vomit and eating in or out of school. Anal swabs from patients, cleaners in school and kitchen workers, as well as water samples were collected for the detection of norovirus nucleic acid. Besides, waterworks were inspected.

Results:
A total of 51 cases were identified, including 40 probable cases and 11 confirmed cases. Besides, 1 asymptomatic cleaner who worked in school. The clinical manifestations were vomiting (66.7%) and diarrhea (60.8%). The cases were clustered in Grade three and dormitory. The incidence rate of male was 17.22% and female was 15.04%. The case-control study demonstrated that drinking barreled water was a risk factor (OR=5.3, 95%CI: 2.3-12.6). The further investigation on the production process of barreled water showed that the main risk factors were the source water was easy to be polluted, the disinfection equipment usually had problems and the disinfectant dosage of washing the barrels was unstable. A total of 12 anal swabs from patients and cleaning worker in school, 3 water samples from infected classes’ barreled water, unopened barreled water and the finished water were positive for norovirus.

Conclusion:
This outbreak was caused by barreled water contaminated by norovirus. It is recommended that the Market Supervision Administration strengthen monitoring, conduct regular sample inspections and supervision in barreled water enterprises to ensure drinking water safety.

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