The incidence of Kawasaki disease (KD) in South Korea decreased sharply after implementation of nonpharmaceutical interventions (NPIs), such as mask wearing and hand washing, were introduced to mitigate the spread of COVID-19, according to a research letter published online June 7 in Circulation.

Ji-Man Kang, M.D., from the Yonsei University College of Medicine in Seoul, South Korea, and colleagues examined whether NPIs were associated with a change in the incidence of KD in Korea, which has the second-highest incidence rate worldwide. Researchers collected data on KD cases among children aged 0 to 19 years from January 2010 to September 2020 from the National Health Insurance Service database. February through September 2020 was defined as the NPI period.

The researchers identified 53,424 cases of KD; 83 percent occurred in children younger than 5 years. The annual mean incidence was 48.1 per 100,000 persons in the pre-NPI period, and the monthly mean incidence was 4.1 per 100,000. KD incidence declined sharply after NPI implementation and plateaued from April. The incidence of KD is usually seasonal, with a minor peak in the late spring and summer and a larger peak in the winter; in the NPI period, this pattern was absent. Considering February to September, the incidence was 18.8/100,000 in the NPI period, corresponding to 60 percent of the mean incidence in the pre-NPI period and 58 percent of the predicted incidence (31.5 and 32.2/100,000, respectively).

"The decrease in the incidence of Kawasaki disease after the implementation of nonpharmaceutical interventions is very clear, and it is unlikely that other independent interventions were accidentally involved," a coauthor said in a statement.

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