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Objective: To evaluate the application of real-time RT-PCR and semi-nested RT-PCR in the detection of norovirus in oysters and analyzing the genetic characteristics of the isolates. Methods: Real-time fluorescent RT-PCR and semi-nested RT-PCR were used to detect norovirus GⅠ/GⅡ in fresh oysters collected from the markets in Beijing from November 2014 to October 2015. The detection rate of the parallel test was also analyzed. In addition, the reliability of semi-nested RT-PCR was evaluated by agreement rate and consistency test (Kappa value). The positive products of norovirus GⅠ/GⅡ capsid protein region gene by semi-nested RT-PCR were sequenced. Software BioEdit 7.0.9.0 was used for sequence alignment, and software Mega 6.0 was used to construct the evolutionary tree. Results: In 72 samples, the detection rate of norovirus was 31.94% (23/72) by real-time RT-PCR, 38.89% (28/72) by semi-nested RT-PCR and 48.61% (35/72) by parallel test. The coincidence rate of the two methods was 73.61%, a moderate degree (Kappa value =0.43). A total of 13 norovirus strains were successfully sequenced, and 11 strains (7 GⅡ.17 strains, 2 GⅡ. 4 Sydney_ 2012 strains, 1 GⅡ. 1 strain and 1 GⅡ. 21 strain) were obtained from norovirus positive samples by two RT-PCR methods, two strains (1 GⅡ. 17 strain and 1 GⅡ. 3 strain) were obtained from real-time RT-PCR negative samples which were positive for norovirus by semi-nested RT-PCR. The similarity between these strains and reference strains from diarrhea patients, environmental sewage, and shellfish products were 84.4% - 100.0%. Conclusions: The parallel test of norovirus in oysters by two RT-PCR methods can improve the detection rate and detect more genotypes. Norovirus strains in oysters were highly homologous with reference strains from diarrheal patients, environmental sewage, and shellfish products. Therefore, surveillance, prevention and control for norovirus should be carried out in people who have frequent contacts with oysters and related environments.

Objective: To study the prevalence of Norovirus infection among kitchen workers in Beijing, and the contamination status of Norovirus in catering companies and train station. Methods: A cross-sectional survey was conducted to collect anal swab specimens and environmental specimens from catering companies in 16 districts of Beijing and in 3 big train stations. Norovirus nucleic acid was detected by fluorescence quantitative PCR. The contamination status of Norovirus in the environment and the asymptomatic infection status of kitchen workers was analyzed in this study. Results: A total of 650 catering companies were investigated. 1 302 anal swabs or stool specimens and 2 600 environmental swabs were collected and tested. Among the 644 catering companies out of train stations, 1 290 anal swabs or stool specimens and 2 576 environmental swabs were collected and tested. The asymptomatic infection rate of Norovirus was 0.85% (11/1 290) among kitchen workers of the catering companies out of the train stations, while the positive rate of norovirus contamination in the environment was 0.04% (1/2 576). Norovirus was not detected in the specimens collected from the kitchen workers and the environment of the catering companies in train stations. Conclusion: During the non-epidemic season of Norovirus in 2019, the infection rate of Norovirus among kitchen workers in Beijing is low, and the environment is contaminated by Norovirus.

Objective: To analyze the influencing factors of acute gastroenteritis outbreaks caused by norovirus in Beijing from 2014 to 2018. Methods: Data of acute gastroenteritis events caused by norovirus in Beijing from April 2014 to March 2018 were collected. Unconditional logistic regression model was conducted to identify the risk factors of the outbreaks. Results: A total of 765 acute gastroenteritis epidemics caused by norovirus were reported in Beijing, in which 85.88 % (657/765) were cluster events and 14.12 % (108/765) were outbreaks. Among the outbreaks, 70.37 % (76/108) were reported in 2017; 84.26 % (91/108) were reported in winter and spring; 88.89 % (96/108) were reported in kindergartens, primary or secondary schools; 81.48 % (88/108) were through person-to-person transmission; 93.52 % (101/108) were caused by norovirus GⅡ infection. The risk of outbreaks in suburban and out suburb area were 1.84 times (95 %CI : 1.13-3.02) and 3.78 times (95 %CI : 1.62-8.82) as high as that in urban area, respectively. The risks of outbreaks in primary, secondary schools and other institutions were 6.26 times (95 %CI : 3.53-11.10), 14.98 times (95 %CI : 6.23-36.01) and 8.71 times (95 %CI : 3.07-24.71) as high as that in kindergartens, respectively. The risk of outbreak in which patients having lower hospital visiting rate than the median rate of all events was 2.29 times than that in the context of having higher hospital visiting rate (95 %CI :1.42-3.68). The risk of foodborne outbreak was 14.55 times as high as that transmitted through person-to-person (95 %CI : 3.15-67.07). Conclusion: Measures such as strengthening the prevention and control of norovirus outbreaks in suburbs, primary schools, secondary schools and other institutions, promoting patients to visit the hospital actively, improving the management of foodborne events and kitchen workers should be taken to reduce the incidence of acute gastroenteritis outbreaks caused by norovirus.