Norovirus Gastroenteritis Outbreak Secondary to Pollution of Water Supply at a University: Jiangsu, China, 2019

  • Water or foodborne
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Background:
From March 19th - 26th, 2019, a university in Jiangsu reported many vomiting and diarrhea cases. To identify the number of cases, find the transmission mode and risk factors, an investigation was conducted.

Methods:
A probable case was defined as any person in the university with following symptoms: vomiting (≥2 times/24h) or diarrhea (≥3 times/24h) from March 16th-29th. A confirmed case was defined as a probable case with norovirus positive stool or anal swab specimen by PCR. Cases search was conducted by using a cellphone survey software. A case control study was conducted to identify the risk factors for transmission. The data were analyzed by SPSS18.0 software, and the counting data were analyzed by Chi-square test. Statistical significance was determined at p < 0.05.

Results:
We identified 1022 probable cases and 64 confirmed cases. The main symptoms included diarrhea (91%), nausea (68%), vomiting (62%). Norovirus was detected in the domestic sewage, 64 students or cooks’ stool or anal swab specimens. Although the secondary water supply pool has been sterilized, there is still one terminal water sample that total coliform group and E. coli exceed the standard. The percentage of cases “eating in canteen from 19th supper to 20th lunch” was 91%, compared to 71% among control group (OR=4.3, 95% CI = 3.4-5.3), the percentage of “roommates vomiting or diarrhea in dormitory” among cases was 77%, compares to 20% among control group (OR=13.1, 95% CI = 11.1-15.5); the percentage of “handling others’ vomit” among cases was 5%, compared to 3% among control group (OR=1.8, 95% CI = 1.3-2.5).

Conclusion:
Secondary water supply polluted by norovirus was the primary cause of the outbreak, foodborne and human-to-human transmission may play an important role. Over 600 norovirus gastroenteritis outbreaks were reported in China during 2014-2017, of which 3.4% were waterborne outbreaks in school. We recommended strengthening guidelines and enforcement secondary water supply disinfection and monitoring in school. Disinfection of vomit should be timely and standardized so as to avoid exposure to students.

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