Molecular epidemiological analysis of gastroenteritis outbreak in a university in Shenyang caused by mixed genotypes of norovirus
Objective To clarify the molecular epidemiological characteristics of a gastroenteritis outbreak in a university caused by mixed genotype norovirus in November 2020 in Shenyang.Methods The epidemiological and clinical information of the outbreak,samples of feces or anal swabs of cases,relevant tableware and other samples were collected.Real-time fluorescence RT-PCR was used to detect major viruses of gastroenteritis(norovirus,etc.).The norovirus-positive samples were amplified by RT-PCR,and PCR products were sequenced.Mega 7.0 software was used for sequence analysis.Results A total of 229 suspected cases were reported in this university from November 16 to 30,2020,with an attack rate of 2.8%(229/8 270).Diarrhea account the highest proportion in the clinical symptoms(92.7%).The difference among various symptoms was statistically significant(x2=46.683,P<0.001).Among the 229 infected patients,the male-to-female ratio was 1:1.79(82:147).All age groups were affected and the highest attack rate was 53.3%(122/229)in<20 years old group.The difference in the attack rates of various occupations in the school was statistically significant(x2=433.049,P<0.001).The detection rates of the 229 samples from cases and 90 environmental samples were 34.1%(78/229)and 8.9%(8/90),respectively.The RT-PCR for genotyping was used to amplify and sequencing for 86 norovirus-positive samples.Nineteen samples were successfully sequenced and were classified into 4 genotypes,including GⅡ.4 Sydney[P16](1,5.3%),GⅡ.6a[P7](11,57.9%),GⅡ.2[P16](5,26.3%)and GⅠ.7b[P7](3,15.8%).One sample was identified as mixed infection of GⅡ.6a[P7]and GⅠ.7b[P7].The similarities of sequences within each genotype ranged from 99.6%to 100%.Conclusions The outbreak was caused by four genotypes of norovirus,and there was case of mixed infection by GⅠ and GⅡ group viruses.This provides a scientific basis for the prevention and control of future outbreaks of gastroenteritis by norovirus in colleges and universities.