An Epidemiologic Investigation for an Outbreak of Norovirus Infection in a Daycare Center in Gyeonggi-Do, Republic of Korea, 2023

<b>Background/Objectives</b>: Norovirus is one of the primary causes of foodborne illness in South Korea. This study aimed to identify the cause of a norovirus outbreak in a daycare center in a city in February 2023 and to prevent further spread through an epidemiologic investigation. <b>Methods</b>: A total of 93 individuals, including daycare staff, children, and kitchen staff, were included. A field epidemiologic investigation was conducted, consisting of case definition, collection of environmental and preserved food samples, and human specimens, along with interviews. A matched case-control study (1:3 ratio) was designed to analyze risk factors, and a statistical analysis, including odds ratios with 95% confidence intervals and chi-square tests, was performed to identify associations between food consumption and infection. Person-to-person transmission was also assessed through epidemiological data analysis. <b>Results</b>: Among the 93 individuals, 16 (17.2%) were identified as cases, of which nine (9.7%) were confirmed cases. The same genotype of norovirus (GII) was detected in eight human samples. No significant association was found between specific food items and infection. The epidemic curve and transmission network analysis suggested that the primary mode of transmission was person-to-person contact within the daycare center. <b>Conclusions</b>: This study highlights the critical role of hygiene practices in daycare settings to prevent person-to-person transmission of norovirus. Regular public health education, environmental disinfection, and early symptom recognition are essential preventive measures.