Case-control study on risk factors for sporadic norovirus infection in residents in Baoshan district, Shanghai

Objective To investigate the risk factors for sporadic norovirus infection in residents in Baoshan, Shanghai. Methods A 1:2 matched case-control study was conducted in 80 norovirus infection cases selected as case group from hospitals in Baoshan from March 1,2015 to April 30,2016,all the cases were laboratory confirmed, and the control group were the people who had no diarrhea or vomiting during the previous two weeks. A self-designed questionnaire was used in the survey. Conditional logistic regression model was used for univariate and multivariate analysis. Results Among the 80 norovirus infection cases, 66 were infected with GⅡ virus (82.50%), 14 were infected with GⅠ virus (17.50%). The results of univariate analysis showed that the risk for norovirus infection in mild manual workers was 2.446 times higher than that in strong manual workers (OR=2.446,95%CI:1.228-4.872). Contact with vomiting and diarrhea patients 3 days before onset (OR=8.267, 95%CI:2.359-28.975), dining out 3 days before onset (OR=2.822, 95%CI:1.467-5.429) and consumption of seafood 3 days before onset (OR=3.000, 95%CI:1.841-4.888) were the risk factors for norovirus infection. Multivariate analysis indicated that contact with vomiting and diarrhea patients 3 days before onset (OR=6.959, 95%CI:1.896-25.537) and consumption of seafood 3 days before onset (OR=2.283, 95%CI:1.336-3.899) were the risk factors for norovirus infection. Washing hands before meals (OR=0.609, 95%CI:0.408-0.909) was a protective factor. Conclusion Norovirus GⅡ was the main pathogen causing intestinal infection in Baoshan. Contact with vomiting/diarrhea patients and consumption of seafood were the possible risk factors for norovirus infection. It is necessary to strengthen the health education and improve seafood safety surveillance.