Background Norovirus (NoV) is the main cause of non-bacterial acute gastroenteritis (AGE) outbreaks worldwide. From September 2015 through August 2018, 203 NoV outbreaks with 2,500 patients were reported to the Shenzhen Center for Disease Control and Prevention. Methods Fecal specimens were collected from the 203 outbreaks and epidemiological data were collected through the AGE outbreak surveillance system in Shenzhen. The genotypes were determined by sequencing analysis. To gain a better understanding of evolutionary characterization of NoV in Shenzhen, the molecular evolution was analyzed by time-scale evolutionary phylogeny and amino acid mutations. Results Most of these outbreaks were associated with NoV GII.P16/GII.2 strain (45.3%,92/203) and occurred in school settings (91.6%,186/203). The timescale phylogeny suggested that the GII.P16/GII.2 strain was recombination strain and were still stable. The amino acid mutations suggested that the nonstructural proteins of the recombination strain might play a more significant role than VP1 gene in these GII.P16/GII.2 recombination strain outbreaks. Conclusions This study illustrated the characteristics of the molecular epidemiological patterns in Shenzhen, China during September 2015 to August 2018 and provided the evidence that the GII.P16/GII.2 strain was static and the epidemic trend had fade.

Background: Norovirus (NoV) is the main cause of non-bacterial acute gastroenteritis (AGE) outbreaks worldwide. From September 2015 through August 2018, 203 NoV outbreaks involving 2,500 cases were reported to the Shenzhen Center for Disease Control and Prevention.Methods: Faecal specimens for 203 outbreaks were collected and epidemiological data were obtained through the AGE outbreak surveillance system in Shenzhen. Genotypes were determined by sequencing analysis. To gain a better understanding of the evolutionary characteristics of NoV in Shenzhen, recombination events were analysed and molecular evolution was evaluated based on time-scale evolutionary phylogeny and amino acid mutations.Results: A total of nine counties reported NoV outbreaks and the reported NoV outbreaks peaked from November to March. Among the 203 NoV outbreaks, 150 were sequenced successfully. Most of these outbreaks were associated with the NoV GII.2[P16] strain (45.3%, 92/203) and occurred in school settings (91.6%, 186/203). The GII.2[P16] strain is a recombinant strain that is relatively stable. In these GII.2[P16] recombination strain outbreaks, the non-structural proteins of the recombination strain might have played a more significant role than VP1.Conclusions: This study illustrates the molecular epidemiological patterns in Shenzhen, China, from September 2015 to August 2018 and provides evidence that the GII.2[P16] strain was relatively stable and that epidemic trend has weakened.