Epidemiological characteristics of norovirus infection outbreaks in schools in Hangzhou, Zhejiang, 2020−2022

Objective To analyze the epidemiological and etiological characteristics of norovirus infection outbreaks in schools in Hangzhou, Zhejiang province and provide evidence for the prevention and control of norovirus infection.

Methods The information about norovirus infection outbreaks in schools in Hangzhou from 2020 to 2022 were collected from public health emergency reporting system. Descriptive epidemiology was conducted to analyze the data related to the distributions, transmission routes, clinical characteristics, and laboratory test results of the norovirus infection outbreaks.

Results A total of 238 norovirus infection outbreaks occurred in 225 schools in Hangzhou during 2020−2022, and a total of 3859 norovirus infection cases were reported, the average attack rate was 2.14% (3859/180506). The median duration of outbreak epidemic was 2 days. Most outbreaks occurred in primary schools (45.38%) and child care settings (44.58%). The outbreaks involving 10−19 cases accounted for 50.42% and the outbreaks involving 3-9 cases accounted for 28.15%. The incidence curve showed a single peak, with high incidence in autumn and winter. The majority of outbreaks were caused by person-to-person transmission (93.70%). The clinical symptoms mainly included vomiting (88.83%), nausea (63.13%) and abdominal discomfort (46.67%). In the outbreaks of norovirus GⅠ and norovirus GⅡ infections, the sample positive rates were 62.30% (114/183) and 66.32% (1229/1853), and in the outbreaks of co-infection of norovirus GⅠ and GⅡ, the sample positive rate was 67.78% (61/90), the differences were not significant (χ²=0.252, P>0.05).

Conclusion Norovirus infection outbreak is prone to occur in primary schools and child care settings. Early control of the outbreak can be achieved by improving surveillance sensitivity and early reporting of the outbreaks