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

BACKGROUND: Norovirus is the predominant pathogen responsible for global acute gastroenteritis outbreaks and sporadic cases. While GII.3[P12] 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.3[P12] norovirus outbreaks in Beijing from August 2021 to July 2023, analyze whole-genome sequences, and infer spread dynamics. RESULTS: GII.3[P12] 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.3[P12] 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). CONCLUSIONS: Our study identified GII.3[P12] 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.