Objective To analyze the epidemiological characteristics and identify the risk factors of an acute gastroenteritis outbreak caused by norovirus in a primary school in Beijing in 2021, suggest preventive measures and recommendations and evaluate the performance of the epidemic response.
Methods Field epidemiology method were carried out. The clinical manifestations and the distribution of the cases were analyzed with descriptive epidemiological method, and a case-control study was conducted to find out the cause of this outbreak. Laboratory tests of enteroviruses and bacterial pathogens were performed by using anal swabs of the patients, food and environment samples.
Results A total of 156 cases were identified, all of which were students, and the attack rate was 24.5% (156/638). The main clinical manifestations of the case were vomiting (98.1%), and no severe cases or deaths were reported. The epidemic curve suggested a point source exposure. Case distribution had obvious spatial clustering and the teaching building, floor and class specific differences in attack rate were significant (P<0.001); The attack rate was 33.1% (95/352) in boys and 26.2% (61/286) in girls, the difference was not significant (χ2=2.736, P=0.098). The results of a case-control study showed that close contact with patients' vomitus (≤1 m) was associated with illness (OR=12.14, 95% CI: 2.76−53.39). Norovirus GⅡ was detected in 57 anal swabs and 3 environmental smear samples.
Conclusion It is an outbreak of acute gastroenteritis caused by norovirus GⅡ, and close contact with vomitus was the main risk factor. Failure in disposal of vomitus in time and delayed reporting of the epidemic were important reasons for this large-scale outbreak. It is suggested for schools to timely clean off vomitus in a standardized manner, strengthen disease surveillance and reporting as well as timely epidemic response to prevent the spread of the epidemic.
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