Epidemiological characteristics of norovirus outbreak in Wenzhou, Zhejiang from 2019 to 2022

Objective To analyze the epidemiological characteristics of norovirus infection in Wenzhou, Zhejiang province, from 2019 to 2022, and to provide evidence for the development of effective prevention and control measures.

Methods The incidence data of norovirus infection outbreaks reported in Wenzhou from 2019 to 2022, including the number of cases, clinical symptoms, epidemiological history, specimen sampling, laboratory results, were collected from the Public Health Emergency Management Information System of Chinese Center for Disease Control and Prevention for descriptively analysis.

Results A total of 69 norovirus infection outbreaks were reported in Wenzhou from 2019 to 2022, involving 1177 cases with an average attack rate of 1.94%.The major clinical symptoms included vomiting (78.84%), bellyache (60.75%), diarrhea (39.42%), nausea (39.25%) and fever (19.88%). The incidence of norovirus epidemics peaked in winter and spring. In the outbreaks, 21 occurred in child care settings, 31 occurred in primary schools, 17 occurred in middle schools. The highest incidence was in childcare settings (3.25%), followed by middle school (1.90%) and primary school (1.69%), the differences were significant (χ²=71.080, P<0.001). Human to human transmission was predominated (67 outbreaks, 97.10%), followed by foodborne transmission (2 outbreaks, 2.90%). The timeliness of outbreak reporting was positively associated with the duration of the outbreak (r_s=0.811, P<0.01). A total of 1665 samples were collected from cases, high-risk population, and environment for nucleic acid testing, in which 504 were positive (30.27%). In the outbreaks, 52 norovirus GⅡ infection ones, while 8 were GⅠ infection ones and 9 were GⅠ/GⅡ infection ones. GⅡ.2 P16 was the most common in positive cases, accounting for 43.09%.

Conclusion All the norovirus infection outbreaks in Wenzhou from 2019 to 2022 occurred in childcare settings, primary schools and middle schools. The surveillance for symptoms, such as vomiting and diarrhea, in child care settings and schools should be enhanced for the early detection of outbreaks and the vomit and excretion of should be disposed appropriately for effective outbreak prevention and control.