Investigation of an outbreak caused by norovirus GⅡ in a school in Wuzhou, Guangxi Zhuang Autonomous Region

  Objective  To analyze the epidemiological characteristics of an acute gastroenteritis outbreak caused by norovirus and identify the risk factors in a school of Wuzhou, Guangxi Zhuang Autonomous Region, in 2021, evaluate the performance of the epidemic response and suggest the targeted prevention and control measures.

  Methods  Field epidemiology survey was carried out. The clinical manifestations and the distributions of the acute gastroenteritis cases were analyzed with descriptive epidemiological method, and a case-control study was conducted to analyze the cause of this outbreak. Samples, such as anal swab, self-supplied well water, tank water, terminal water of public water supply system, object surface swab, and food sample, were collected from the typical cases for the detection of nucleic acid of norovirus and other common pathogens.

  Results  A total of 142 acute gastroenteritis cases were reported, with an attack rate of 5.55% (142/2 559). The main clinical symptoms were vomiting (83.10%), abdominal pain (83.10%), fever (67.61%), nausea (63.38%) and diarrhea (50.70%). There was a statistical difference in the attack rate among students in different dormitory buildings (χ²=36.978, P<0.001). The results of the case-control study showed that gargle with self-supplied well water (OR=3.78, 95%CI: 1.736−8.234) and contact with acute gastroenteritis case (OR=2.97, 95% CI : 1.465−5.312) were the main risk factors. There was a dose-response relationship between the frequency of gargle with self-supplied well water and the attack rate (χ²=14.935, P=0.002). Norovirus GⅡ was detected in 8 anal swabs, 1 vomitus sample and water samples from well A and tanks.

  Conclusion  This outbreak was caused by the infection norovirus GⅡ, possibly resulting from well water pollution in environment and human-to-human transmission. Gargle with self-supplied well water and exposure to acute gastroenteritis case were the major risk factors. The lack of appropriate water treatment equipment and the failure to isolate acute gastroenteritis cases in time were the major reasons for the spread of the epidemic. It is recommended to strengthen the hygienic management of self-supplied well water to reduce the risk of outbreaks. Otherwise, we suggest schools and child-care settings to strengthen the management of infectious disease and conduct timely reporting and response of outbreaks to prevent the spread of the epidemic.