Exploring viral infections' role in Kawasaki disease onset: A study during the COVID-19 pandemic.

During the coronavirus disease 2019 (COVID-19) pandemic, known viral diseases declined in all ages. By using the current situation as a natural experiment, this study aimed to evaluate whether the change in the incidence of Kawasaki disease (KD) during the COVID-19 pandemic varies with age and whether a specific infectious disease mediates the occurrence of KD. Monthly number of KD patients were extracted from the nationwide inpatient database. Segmented regression analysis was conducted on the interrupted time series data. Additionally, causal mediation analysis was performed to examine the role of viral infections in the changes in the number of KD patients. After the first emergency declaration for COVID-19 in Japan, there was an immediate decrease in the number of KD patients per 100 000 population aged between 6 months and 4 years (immediate change = -2.66; 95% confidence interval [CI]: -5.16 to -0.16) and aged 5-15 years (immediate change = -0.26; 95% CI: -0.49 to -0.04). However, no immediate change was observed in patients under 6 months of age. In the causal mediation analysis for each viral infection, it was found that the decrease in the number of patients with KD was mediated by changes in the number of patients with pharyngoconjunctival fever and infectious gastroenteritis. The current results suggest that viral infections may be one of the etiological agents for KD, while they may not be the main cause in early infancy. Specifically, we found that adenovirus infection and gastroenteritis was closely related to the onset of KD in some areas of Japan.