Analysis of Meteorological Factors Contributing to the February 2025 Epidemic of Infectious Gastroenteritis and Norovirus Food Poisoning Outbreaks in Japan Using Open Data

In February 2025, the number of norovirus (NoV) food poisoning outbreaks in Japan increased markedly, and a large-scale epidemic of infectious gastroenteritis was observed, peaking between February and March. During this period, many regions in Japan experienced a winter-type pressure pattern, resulting in below-average temperatures. Given these conditions, we analyzed the relationships between the incidence of infectious gastroenteritis and NoV food poisoning and meteorological factors (temperature, precipitation, and humidity) using open data. Specifically, we examined the associations between deviations in the number of infectious gastroenteritis cases from the five-year average and differences in temperature, precipitation, and humidity from climatological norms in each prefecture. The analysis revealed that lower temperatures and reduced humidity in February 2025 were associated with an increased incidence of infectious gastroenteritis. In particular, decreased temperatures in western Japan and reduced humidity in the Kanto region were significantly associated with the epidemic. In contrast, no association was observed with NoV food poisoning, likely due to the involvement of food hygiene-related factors and the limited number of samples. Furthermore, the predicted incidence of infectious gastroenteritis, generated by a multiple regression model using meteorological factors as explanatory variables, showed a significant correlation with observed values, indicating the potential utility of this model for forecasting future epidemics of infectious gastroenteritis.