Surge of group waterborne and foodborne diseases from increased norovirus GII.4 transmission in Seoul childcare centers and kindergartens in 2022

Abstract Norovirus is the most common cause of group waterborne and foodborne diseases (GWFD) in childcare centers and kindergartens. Its high transmissibility is partly due to its genetic diversity. GWFD cases that occurred in Seoul childcare centers and kindergartens from 2019 to 2022 were investigated, and 68 epidemiological reports prepared by public health centers in Seoul were used for data collection. In the three quarters of 2022, there were 40 cases of GWFD in Seoul childcare centers and kindergartens, which exceeded the 35 total cases that occurred during the previous three years. The proportion of Seoul childcare centers and kindergartens with GWFD cases increased from 12.6% in 2019 to 58.8% in 2022. Norovirus was the most common pathogen responsible for GWFD in these cases. From 2019 to 2021, norovirus GII.2 was the predominant genotype, and GII.4 was detected in about 25% of cases. However, in 2022, GII.4 became predominant and was detected in about 79% of cases. The attack rate and infection source of GWFD cases from 2019 to 2021 were not significantly different from those in 2022. In conclusion, the number of GWFD cases in Seoul childcare centers and kindergartens significantly increased, primarily because of increased norovirus GII.4. transmission in 2022.