Molecular Epidemiology of Norovirus Outbreaks in Childcare Centers and Schools in South Korea in 2023.

Norovirus is a leading cause of acute gastroenteritis and foodborne illness worldwide. In this study, we investigated the epidemiologic and molecular characteristics of norovirus outbreaks in childcare centers and schools in South Korea throughout 2023. A total of 141 stool samples collected from these outbreaks were confirmed positive for norovirus using real-time and conventional RT-PCR, and subsequently analyzed for genotype. The reported outbreaks were most frequently observed in the provinces of Gyeonggi (31.2%) and South Gyeongsang (20.6%), followed by Seoul (12.1%). Outbreaks were most frequently associated with childcare centers (38.3%), primary schools (36.2%), and kindergartens (13.5%). Seasonally, 51.8% of cases occurred during the winter months (November-March), with a peak observed in April. Genotypic analysis revealed that 95.6% of cases were caused by GII norovirus, with the GII.2[P16] genotype being the most prevalent (34.5%). Notably, foodborne transmission was implicated in 13.5% of cases, predominantly involving the GII.2[P16] and GII.6 genotypes. Unlike previous studies that report norovirus genotypes from clinical cases of acute gastroenteritis, our analysis included cases from foodborne outbreaks, thereby offering deeper insights into the role of contaminated food in facilitating norovirus transmission. Furthermore, childcare centers were the primary setting for detection of the GII.4[P16] and GII.4[P31] genotypes, while primary schools exhibited the greatest genotypic diversity, with 12 distinct genotypes identified. These findings indicate a potential shift in norovirus seasonal patterns, with outbreaks extending into late spring. Overall, our results underscore the need for enhanced hygiene practices, robust surveillance systems, and targeted prevention strategies to mitigate norovirus transmission.