Increased GII.3P12 norovirus outbreaks and viral whole genome analysis in Beijing, China during 2021 and 2023

Norovirus is the predominant pathogen responsible for global acute gastroenteritis outbreaks and sporadic cases. While GII.3P12 norovirus is typically associated with sporadic cases of acute gastroenteritis, outbreaks caused by this genotype increased sharply in Beijing from 2021 to 2023. This study aimed to characterize the GII.3P12 norovirus outbreaks in Beijing from August 2021 to July 2023, analyze whole-genome sequences, and infer spread dynamics. GII.3P12 outbreaks primarily occurred in winter and spring (90.68%, 107/118), concentrated in urban areas (56.78%, 67/118). Ninety-three outbreaks (78.81%, 93/118) were reported in kindergartens. Person-to-person transmission was the main route, accounting for 99.14% (115/116) of outbreaks with a defined route. The maximum clade credibility tree, constructed from partial viral capsid protein 1 and RNA-dependent RNA polymerase genes, showed that GII.3P12 strains are clustered into three clades, aligning with analyses of 82 whole-genome sequences. Bayesian inference revealed that the most recent ancestor for the three clades of the maximum clade credibility tree based on whole-genome sequences was 2015.66, 2016.56, and 2017.71, respectively, and urban areas are key transmission hubs. The histo-blood group antigens binding sites were conserved, and there were some unique amino acid mutations in the open reading frame 1 region: clade 1 (V779I/D870G/K1004R/I1057V/I1521V), clade 2 (A21V/S195L/R278K/V779I/A782V/A791V/I850T/P1051S/V1091A/S1571T), and clade 3 (T701I). Our study identified GII.3P12 as the dominant strain in norovirus outbreaks in Beijing, China (2021–2023). We obtained 82 whole-genome sequences via next-generation sequencing, revealing amino acid mutation-driven evolution, inferring local transmission dynamics, and providing insights for outbreak control and vaccine development.