Regional Differences in Kawasaki Disease Incidence Reduction Before and After the Onset of the Coronavirus Disease 2019 Pandemic.

OBJECTIVE: To assess regional differences in reduction of the incidence of Kawasaki disease during the mitigation period for the coronavirus disease 2019 pandemic, with a hypothesis that more sparsely populated regions have fewer opportunities for human-to-human contact, resulting in a greater reduction in the incidence of Kawasaki disease. STUDY DESIGN: A retrospective ecological study was conducted using data from patients hospitalized for Kawasaki disease as well as infectious diseases surveillance reports in Shiga Prefecture, Japan, during 2015-2020. We defined the periods before and after the onset of pandemic as January 2015-March 2020 and as April 2020-December 2020, respectively. We compared the reductions in the incidence of Kawasaki disease among 6 administrative regions in the prefecture according to the density of the populations. RESULTS: A total of 1290 patients with Kawasaki disease were identified. The incidence of Kawasaki disease (per 100 000 person-years) was significantly reduced after the coronavirus disease 2019 pandemic onset (period before pandemic onset, 105.6 [95% CI 99.8-111.8]; period after pandemic onset, 68.6 [95% CI 56.7-83.0]). During the period after pandemic onset, the incidence of Kawasaki disease was significantly reduced in May, compared with the corresponding period in previous years. The number of patients aged 2-4 years was significantly reduced after the pandemic onset. Notably, greater reductions in the incidence of Kawasaki disease were found in regions with lower population densities. CONCLUSIONS: Assuming that there were fewer opportunities for human-to-human contact in more sparsely populated regions during the pandemic mitigation period, our findings support the hypothesis that human-to-human contact may be associated with development of Kawasaki disease.

Kawasaki Disease and Pediatric Infectious Diseases During the Coronavirus Disease 2019 Pandemic.

OBJECTIVE: To assess the epidemiologic association between Kawasaki disease and common pediatric infectious diseases (PIDs) identified during the coronavirus disease 2019 (COVID-19) pandemic period to confirm whether the infection-triggered theory is a plausible hypothesis for the pathogenesis of Kawasaki disease. STUDY DESIGN: A retrospective epidemiologic study was conducted using datasets obtained from Web-based surveillance of Kawasaki disease and PIDs in Japan. We compared weekly numbers of patients who developed Kawasaki disease and specific PIDs between 2020 and 2017-2019 and evaluated the association between the percent reduction in the number of patients with these diseases. RESULTS: A total of 868 patients developed Kawasaki disease in 2020. During the social distancing period in 2020, the number of patients with Kawasaki disease was approximately 35% lower than in 2017-2019. Time from the onset of Kawasaki disease until the first hospital visit did not differ significantly among the examined years. The proportion of older children with Kawasaki disease decreased more than that of infants with Kawasaki disease (age <1 year), resulting in a significant difference in the proportion of infant patients between 2020 and 2017-2019 (24% vs 19%; P < .01). The number of patients with incomplete Kawasaki disease was unchanged from that of previous years. The weekly percent reduction in patient numbers differed between Kawasaki disease and PIDs during 2020, with no strong correlation between the 2 diseases. CONCLUSIONS: Our data indicate that parents of patients with Kawasaki disease did not avoid hospital visits during the COVID-19 pandemic period. The findings indicate the possibility that triggering Kawasaki disease might be associated with presently unidentified respiratory pathogen(s) that potentially might be acquired from both within and outside the household.

Epidemiology, Treatments, and Cardiac Complications in Patients with Kawasaki Disease: The Nationwide Survey in Japan, 2017-2018.

OBJECTIVE: To report the epidemiologic characteristics, treatments, and cardiac complications of Kawasaki disease, using data from the nationwide survey in Japan. STUDY DESIGN: The nationwide Kawasaki disease survey in Japan has been conducted biennially since 1970. The most recent survey was completed in 2019, obtaining information for patients who developed Kawasaki disease during 2017-2018. Survey respondents were hospitals specializing in pediatrics and those with ≥100 beds and a pediatric department throughout Japan, where patients with Kawasaki disease were eventually hospitalized. RESULTS: The survey identified 32 528 patients with Kawasaki disease, which consisted of 15 164 (46.6%) in 2017 and 17 364 (53.4%) in 2018. The highest annual incidence rate was recorded in 2018 (359 per 100 000 children aged 0-4 years). After 1982, patients with ≤4 principal Kawasaki disease signs gradually increased, resulting in 6847 (21.1%) patients diagnosed during 2017-2018. Among the 30 784 patients receiving initial intravenous immunoglobulin administration, 6061 (19.7%) did not respond. Within 30 days of Kawasaki disease onset, 9.0% of patients were diagnosed with cardiac complications, and 2.6% of patients developed cardiac sequelae after the acute illness. CONCLUSIONS: The annual number of patients developing Kawasaki disease in Japan increased from 1970 through 2018, whereas the proportion of patients with Kawasaki disease with cardiac complications decreased in the most recent 2 decades. Early diagnosis of Kawasaki disease as well as advances in initial treatments could explain these findings.