Molecular Epidemiology of Norovirus Outbreaks in Food-Catering Facilities in Busan, 2021–2024

Norovirus is the leading cause of foodborne illness outbreaks worldwide and represents a significant public health concern.Highly contagious and responsible for acute gastroenteritis, norovirus spreads rapidly through contaminated food, water, and direct person-to-person contact.Owing to extensive genetic diversity, individuals may experience repeated infections, with limited cross-protection across genotypes.This study investigated the molecular epidemiology of norovirus outbreaks in food-catering facilities in Busan, Korea, from 2021 to 2024.Among 1,546 stool specimens analyzed, 394 (25.5%) tested positive, comprising 19 genogroup I (4.8%) and 375 genogroup II (95.2%) strains, which represented 12 genotypes (5 GI and 7 GII).Outbreaks occurred most frequently in childcare centers, elementary schools, and kindergartens.Although annual variation in genotype prevalence was observed, GII.4 remained the predominant strain throughout the study period.In 2024, GII.7 was identified for the first time, consistent with strains detected in patients with acute diarrhea in Busan, and GII.17-previously responsible for large outbreaks more than a decade earlier-also re-emerged.These findings underscore the dynamic circulation of norovirus genotypes in community settings and highlight the importance of continuous molecular surveillance.Such efforts are essential for the early detection of emerging variants, improved outbreak prevention, and the development of effective vaccines targeting persistent and high-burden genotypes such as GII.4.