Objective  To describe the epidemiological characteristics and environmental factors of a norovirus infection outbreak that occurred in an university in Lanzhou, 2020, and provide evidence for the prevention and control of norovirus infection.

  Methods  A questionnaire survey was conducted to collect the incidence data of norovirus infection in the outbreak. Rectal swab and stool samples from healthy students, sick students and others, and environmental swab smears were used for norovirus detection. Norovirus (GⅠ/GⅡ) nucleic acid detection kit was used to detect all the samples by real-time fluorescence polymerase chain reaction (RT-PCR). Partial RNA-dependent RNA polymerase and capsid nucleotides of GⅡ norovirus-positive samples were amplified and analyzed. Norovirus genotypes were identified by online genotyping tool and χ² test was used to compare the rates.

  Results  A total of 459 norovirus infection cases occurred in this outbreak, with an attack rate of 3.01%. The attack rate in women (3.75%) was higher than that in men (2.13%), and the difference was significant (χ²=34.185, P<0.001). There were significant differences in the attack rate among the students from four areas of dormitory A, B, C, and D (χ²=32.314, P<0.001). The norovirus attack rate was highest in area D (3.73%), with the cases accounting for 64.05% of the total. The positive rates of norovirus in diarrhea and asymptomatic groups were 78.52% and 40.82%, respectively. The difference was significant between two groups (χ²=6.760, P=0.009). There was no significant difference in positive rate of norovirus between cafeteria employee group and logistic manager group (χ²=0.062, P=0.803). Environmental testing for norovirus had negative result. Genotyping indicated that norovirus identified in this outbreak belonged to GⅡ.P17-GⅡ.17.

  Conclusion  This outbreak might be an imported one by student returning after vacation, but contact transmission could not be excluded.