The incidence of Kawasaki Disease has a peak in the winter months with a trough in late summer/early fall. Environmental/exposure factors have been associated with a time-varying incidence. These factors were altered during the COVID-19 pandemic. The study was performed through the International Kawasaki Disease Registry. Data from patients diagnosed with acute Kawasaki Disease and Multiple Inflammatory Syndrome-Children were obtained. Guideline case definitions were used to confirm site diagnosis. Enrollment was from 1/2020 to 7/2023. The number of patients was plotted over time. The patients/month were tabulated for the anticipated peak Kawasaki Disease season (December-April) and non-peak season (May-November). Data were available for 1975 patients from 11 large North American sites with verified complete data and uninterrupted site reporting. The diagnosis criteria were met for 531 Kawasaki Disease and 907 Multiple Inflammatory Syndrome-Children patients. For Multiple Inflammatory Syndrome-Children there were peaks in January of 2021 and 2022. For Kawasaki Disease, 2020 began (January-March) with a seasonal peak (peak 26, mean 21) with a subsequent fall in the number of cases/month (mean 11). After the onset of the pandemic (April 2020), there was no clear seasonal Kawasaki Disease variation (December-April mean 12 cases/month and May-November mean 10 cases/month). During the pandemic, the prevalence of Kawasaki Disease decreased and the usual seasonality was abolished. This may represent the impact of pandemic public health measures in altering environmental/exposure aetiologic factors contributing to the incidence of Kawasaki Disease.
Keywords: COVID-19; Kawasaki Disease; international Kawasaki Disease Registry; multisystem inflammatory syndrome-children; paediatric inflammatory multisystem syndrome; seasons.