| BackgroundNoroviruses(NoV)are the leading cause of human acute gastroenteritis.NoV evolved rapidly and recombination was one of the important ways of its evolution.In recent years,the outbreaks caused by recombinant strains have shown an upward trend in China.Qian,from China,collected the NoV sequences of all Chinese regions uploaded to Genbank(as of May 2016),and found that Guangdong and Hong Kong are the centers of NoV transmission in China through virus migration model study.Shenzhen is one of the central cities in Guangdong with a large floating population and has high possibility of virus recombination.However,the epidemiological study of NoV outbreaks in Shenzhen and the evolution of dominant strains still lack comprehensive systematic data.The purpose of this study was to investigate the epidemiology of NoV outbreaks in Shenzhen and the evolution of GII.P16/GII.2 strain,as well as to improve the basic data of NoV outbreaks in Shenzhen,and to provide a scientific basis for NoV outbreak prevention and control.Methods1.Collect samples of NoV outbreak-positive diarrhea in Shenzhen from September 2015 to August 2018,record basic information on outbreak epidemiology,and analyze epidemiological characteristics using statistical methods.2.Amplification polymerase region and the capsid region of the sample by RT-PCR method for genotyping.3.The nested landing PCR amplification of the whole genome sequence was carried out on the GⅡ.P16/GⅡ.2 samples from Shenzhen.4.Recombination,evolution and diversity analysis of GⅡ.P16/GⅡ.2 NoV in Shenzhen using software such as BEAST v1.8.2 and MEGA6.0.Results1、From September 2015 to August 2018,a total of 203 outbreaks were detected in Shenzhen,and 21,112 and 70 outbreaks were monitored in the three year.The frequency of outbreaks in each administrative district is different.The total number of patients involved is 2,500.The peak of the outbreak was from November to March.The number of outbreaks in school-based places accounted for 91.6%,and non-schools accounted for 8.4%.There was a significant difference between the two settings2、Sequencing analysis results:The number of successful sequencing was 150,and 15 capsid types and 15 polymerase types were detected.The main capsid and polymerase regions were GII.2(61.3%)and GⅡ.P16(61.3%),respectively.3、Evolutionary analysis showed that the GⅡ.P16/GII.2 polymerase region in Shenzhen had the shortest evolutionary distance with the GⅡ.P16/GⅡ.4 Sydney2012 detected in 2015～2016,and the capsid region had The shortest evolutionary distance with the GⅡ.P16/GⅡ.2 detected in 2010～2012,The formation time of the polymerase region and the capsid region was between 2012-2013 and 2013-2014,respectively.4、In the amino acid variation site analysis,no mutation sites were found in the capsid region,and 10 amino acid-specific mutation sites were found in the non-structural region.5、Genetic diversity analysis showed that most of the early sequences were in the same branch as Hong Kong strain,and a small number of sequences were in the same branch as the Taiwan or Japan strains.Conclusion1、From September 2015 to August 2018,the most frequent outbreaks in Shenzhen were from September 2016 to August 2017,with obvious regional distribution and seasonal distribution characteristics.The outbreaks were mainly school-based.The genotype causing the outbreak has diversity,and the dominant strain is GⅡ.P16/GⅡ.2 NoV.2、Recombinant strains of GⅡ.P16/GⅡ.2 strains in Shenzhen area may have been reconstituted as early as 2013-2014.The main mechanism of the outbreak in the population might be the change of non-structural region.There may be multiple routes for the introduction of GⅡ.P16/GⅡ.2 recombinant strain into Shenzhen. |
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