ABSTRACT
Background: Several lines of evidence suggest that Kawasaki disease (KD) results from exposure of genetically predisposed individuals to unidentified, possibly infectious or environmental, triggers. Recent epidemiological studies have suggested that KD development may be linked to winds that potentially carry triggers. However, the triggers and transmission modes remain to be determined.Methods: We implemented a longitudinal observational study in Fukuoka Children’s Hospital and five adjacent general hospitals from February to May in 2017 to 2020. We investigated the impact of the nationwide State of Emergency for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak on the incidence of KD in comparison with that of infectious diseases.Findings: The number of admissions for KD (total n=356) showed no significant change in April–May 2020 compared with that in April–May 2017–2019 (18·0/month vs. 23·8/month, p=0·10, 24·5% decrease). Meanwhile, the number of patients admitted for droplet or contact-transmitted respiratory tract and gastrointestinal infections (total n=2544) showed a significant decrease in April–May 2020 (respiratory tract infections: 39·0/month vs. 151·5/month, p<0·0001, 74·3% decrease; gastrointestinal infections: 6·0/month vs. 44·8/month, p<0·0001, 86·6% decrease). Thus, the ratio of KD to droplet or contact-transmitted respiratory tract and gastrointestinal infections in April–May 2020 was significantly increased (p<0·0001). Although the clinical features of KD were slightly milder, there were no significant differences between those admitted in April–May 2020 and those admitted in April–May 2017–2019. None of the patients with KD in Fukuoka in 2020 were associated with SARS-CoV-2 infection.Interpretation: The significantly increased incidence of KD relative to respiratory tract and gastrointestinal infections during the COVID-19 State of Emergency suggests that contact or droplet transmission is not a major route for KD development, and that KD may be an airborne disease in most cases. Funding: Fukuoka Children’s Hospital Research Grant.Declaration of Interests: The authors declare no competing interests and no financial support for this study. Ethics Approval Statement: The research protocol (FCH:2020-9) was approved by the Ethical Committees of all participating hospitals. This was a retrospective study and it was difficult to obtain consents directly. Therefore, we revealed the contents of the study on the websites, and informed consent was substituted with opt-out.