An Increasing Prevalence of Non-GII.4 Genotypes Causing Norovirus Gastroenteritis Outbreaks - Beijing Municipality, China, 2017-2024.

OBJECTIVES

Since 2014, non-GII.4 norovirus genotypes have increasingly challenged the predominance of GII.4, particularly in Asia. This study analyzed the epidemiological and genetic characteristics of norovirus outbreaks from January 2017 to June 2024 in a district of Beijing, China.

METHODS

We tested 2,016 stool samples collected from 309 acute gastroenteritis outbreaks for norovirus using real-time RT-PCR. Partial polymerase and capsid sequences of norovirus-positive samples were amplified and sequenced for phylogenetic analysis. Additionally, we performed genome amplification and sequence analysis on seven GII.7[P7] strains.

RESULTS

Between January 2017 and June 2024, 150 norovirus outbreaks were reported, with GII norovirus causing 83.3% of these outbreaks. We identified 16 distinct genotypes. Among the 102 GII genotype outbreaks, non-GII.4 norovirus outbreaks (81.4%) significantly outnumbered GII.4 norovirus outbreaks (18.6%). The three most prevalent genotypes during the study period were GII.2[P16] (46.1%, 47/102), GII.3[P12] (14.7%, 15/102), and GII.4 Sydney[P16] (12.7%, 13/102). GII.2[P16] predominated in 2017, 2018, and 2020, while GII.3[P12] was the dominant genotype in 2022. Multiple genotypes emerged in 2023. In the first half of 2024, GII.4 Sydney[P16] became predominant (36.9%), while a novel GII.7[P7] variant emerged, accounting for 26.3% of outbreaks. All seven GII.7[P7] genome sequences formed an independent branch in both VP1 and polymerase regions.

CONCLUSIONS

Our findings demonstrate that non-GII.4 noroviruses play an increasingly important role in outbreaks in Beijing. Continuous surveillance is needed to better understand and control norovirus outbreaks in future epidemic seasons.