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The following paper investigates the prevalence and characteristics of asymptomatic norovirus infection in the population living around oyster farm sites. Two consecutive surveys were conducted from January 2014 to December 2014 and 4549 stool samples were screened during the same time period. The total asymptomatic infection rate was 4.04% (184/4549). Norovirus infection rate was 5.20% in oyster farming population which was significantly higher compared with non-farming population where the infection rate was 3.65% (χ2 = 5.49, P < 0.05). A total of 184 NoV positive samples were identified by real time-quantitative polymerase chain reaction (RT-qPCR) and semi-nested RT-PCR and 136 sequences were obtained. The sequences were clustered into 14 genotypes. GI strains were clustered into six genotypes, including GI.2, GI.3, GI.5, GI.6, GI.8 and GI.9; while GII strains were clustered into GII.2, GII.3, GII.4, GII.5, GII.6, GII.8 and GII.13. GI.9 and GII.17 were the predominant and most prevalent genotypes, respectively. The GII.17 genotype replaced GII.4 becoming the dominant genotype in the oyster farming area in 2014. To sum up, long-term monitoring of asymptomatic infection is crucial for the detection of new variant strains and for identifying outbreaks during the early stage.

Objective: To have an insight into the prevalence tendency caused by Noroviruses( NoVs) in population of oyster farming areas, and evaluate the early warning signification of acute gastroenteritis( AGE) monitoring., Methods: Between January and December in 2014, a retrospective household survey of AGE during past four weeks was conducted to residents using multi-stage sampling in oyster farming areas. Norovirus capsid genome was detected using real-time RT-PCR and semi-nested PCR, sequenced and phylogenetic analyzed., Results: A total of 75 cases of AGE were reported. The incidence rate was 0. 10 per person-year, the detection rate of norovirus was 20. 0%( 15 /75). The dominant epidemic No Vs strain in oyster farming was still GII. 4 Sydney 2012. Furthermore, a newly GII. 17 variant was detected and early in March 2014., Conclusion: The GII. 4 Sydney 2012 genotype is still prevalent strain that caused AGE currently in the community residents of oyster farming areas. NoVs GII. 17 variant was found in sporadic patients of sentinel hospital AGE monitoring in March 2014 that have an early warning effect to the outbreaks of winter in 2014.