Increase in Sapovirus Infection in Korea After the COVID-19 Pandemic: A Six-and-a-half-year Retrospective Study.

BACKGROUND: Sapovirus is an increasingly recognized cause of acute gastroenteritis (AGE). Despite its significance, data on sapovirus epidemiology and genetic diversity in Korea are limited. Therefore, we examined sapovirus positivity rates over a 6.5-yr period and analyzed the genetic diversity of strains detected in 2022 in Korea. METHODS: We retrospectively analyzed 204,563 sapovirus multiplex PCR test results from suspected AGE cases collected between 2017 and 2023 at two institutions. Monthly and age-specific positive rates were evaluated. Forty sapovirus-positive samples from 2022 were genotyped using reverse transcription PCR and sequencing. The sequences were compared with those in the National Center for Biotechnology Information Virus database, and a phylogenetic tree was constructed to assess genetic relationships among sapovirus strains. RESULTS: The overall sapovirus positivity rate from 2017 to 2023 was 2.2%, with an increasing trend in summer and autumn, except during the coronavirus disease 2019 (COVID-19) pandemic in 2020 and 2021, when sapovirus was rarely detected. Positivity markedly increased in the summer and autumn of 2022 and 2023 following the COVID-19 pandemic. The predominant genotypes in 2022 were GI.1 and GII.3. Phylogenetic analysis revealed genetic diversity among circulating strains. CONCLUSIONS: This study highlights the rising incidence of sapovirus in Korea, particularly after the COVID-19 pandemic. Despite focusing on genotyping data from a single year, these findings emphasize the need for ongoing surveillance to monitor sapovirus evolution and its public health impact. Additionally, our findings provide essential baseline data for future research into the epidemiology and genetics of sapovirus.