Abstract: This study experimentally investigated and analyzed the genotype and epidemiological features of norovirus isolated from oys-ters collected from the market in Shanghai, to provide strong support for the prevention and control of NoV and the risk assessment ofoyster consumption. To avoid contingency, oysters were randomly collected in Shanghai from October 2017 to October 2019. Then, NoV was detected by applying nested RT-PCR. And, norovirus genotyping tool integrated with phylogenetic was used to analyze se-quences and genotyping. Genotype and epidemiological analyses were performed in terms of temporal distribution and genotype distribu-tion. A total of 633 oyster samples were detected, with a positive rate of 22.1% (140 /633). Eight genotypes were found in oysters,mainly included GI. 3 (62 cases), GI. 4 (21 cases), GI. 9 (1 case), GII. 4 (30 cases), GII. 3 (29 cases), GII. 12 (13 cases),GII. 2 (6 cases) and GII. 17 (4 cases). The collected data showed that peak season for NoV outbreak in oysters occured from Novem-ber to February. For the first year (89. 4%), GI was given priority, such as GI. 3 (67. 1%) and GI. 4 (22. 4%). However, GII wasdominated in the second year (90. 1%), including GII. 3 (35. 8%), GII. 4 (30. 9%), GII. 12 (12. 3%), GII. 2 (7. 4%) and GII.17 (3. 7%) respectively. Total 25 cases of GII. 3 and GII. 4, 1 case of GII. 9 and GII. 3 were detected by showing co-contamination.The results showed that the dominant genotype could change from GI to GII within two years, which helped to predict that it was likelyto be affected by external factors, such as human activities. Therefore, the study appealed to strengthen the control of water quality andhuman activities in oyster farms to reduce outbreaks of NoV, which had strong winter seasonality of outbreaks. Furthermore, epidemic strains of NoV among humans were still circulating in the environment. Multi-genotypes co-contamination not only gave chances for NoVgenetic recombination, but also exacerbated the risk of oyster consumption for Norovirus. Therefore, relevant departments should in-crease the intensity of conducting propaganda to warn people not to eat oysters, especially raw oysters during NoV􀆳s high-occurrence season during the winter.

Key words: norovirus, oysters, contamination, genotype, epidemiological trends