Objective   To investigate the epidemiological characteristics and identify the cause of a norovirus infection outbreak in a kindergarten of Xi′an in 2021, and the pathogen was identified by molecular typing.

  Methods   Active case finding was carried out according to the definition of suspected norovirus cases, and field hygienic survey was conducted. The clinical manifestations and the distribution of the cases were described with descriptive epidemiological method, and cohort-study was used to find out the cause of this outbreak. Anal swab samples were collected from typical cases for norovirus nucleic acid detection and gene sequencing.

  Results   This norovirus outbreak lasted for 3 days, and a total of 31 cases were reported, all the cases were children, with an average attack rate of 14.16% (31/219). Among them, the cases aged 4-year-old accounted for the highest proportion (93.55%, 29/31), and the class 4 of grade 1 had the highest attack rate (40.00%, 12/30). The main clinical symptoms were vomiting (100%), diarrhea (12.90%) and abdominal pain (6.45%). No severe cases or deaths were reported. The epidemic curve showed that the outbreak was caused by one-time same source exposure. The cohort-study showed that the risk of close exposure to vomit was 3.98 times higher than that of long-distance exposure (RR=3.98, 95% CI:2.159–7.334). The positive rate of norovirus in case samples was 61.54% (8/13). Gene sequencing and type identification indicated that the pathogen was norovirus GⅡ.3P12.

  Conclusion   This outbreak was caused by the exposure to aerosols from vomit of the index case, and the pathogen was norovirus GⅡ.3P12 . It is necessary to strengthen the training of staff in child care settings on norovirus prevention and control, especially on emergency disposal of excreta and vomit, to prevent such epidemics.