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The etiologic agent responsible for the clinical and pathologic findings in Kawasaki disease (KD) has long remained elusive, although human-to-human transmission of a respiratory pathogen has been hypothesized. Since 2001, Japan's biennial survey of pediatric hospitals has revealed a steady increase in the number of patients with KD. Has the COVID-19 pandemic, with its mitigation measures, affected this pattern? Researchers in Japan conducted a cohort study to determine KD rates from January 2019 through December 2020, capturing the year before and one year during the pandemic.
In all, 17,347 cases of KD were reported in 2019 compared with 11,173 in 2020, a 36% reduction during the first year of the COVID-19 pandemic. Children diagnosed in 2020 compared with 2019 were younger (25 vs. 26 months), and more were younger than 12 months at diagnosis (22% vs. 19%). Children younger than 12 months (significantly, those too young to mask) showed more-moderate declines in KD incidence than older children and had later rebound following the relaxation of COVID-19 mitigation measures. There was no significant difference in number of days of illness at presentation, making reluctance to seek medical care an unlikely explanation for the decline in incidence.
Ae R et al. Incidence of Kawasaki disease before and after the COVID-19 pandemic in Japan: Results of the 26th nationwide survey, 2019 to 2020. JAMA Pediatr 2022 Oct 17; [e-pub]. (https://doi.org/10.1001/jamapediatrics.2022.3756)
Comment
The COVID-19 pandemic had some unexpected effects. Respiratory illnesses such as influenza and respiratory syncytial virus faded into the background, only to reappear now in massive numbers. The significant declines in KD incidence in Japan during the pandemic support a respiratory pathogen as a catalyst for the syndrome. Now that COVID-19 mitigation measures have relaxed and respiratory viruses have returned, clinicians will have to be on the lookout for KD as case numbers will likely rise.