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Incidence of Kawasaki Disease Before and After the COVID-19 Pandemic in JapanResults of the 26th Nationwide Survey, 2019 to 2020

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To identify the key insights or developments described in this article
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Key Points

Question  Did the COVID-19 pandemic and its accompanying mitigation measures affect the incidence of Kawasaki disease (KD) in Japan?

Findings  In this cohort study of 28 520 patients, the number of patients diagnosed with KD decreased by approximately one-third across Japan in 2020 (after the COVID-19 pandemic) compared with 2019 (before the pandemic), with no indication suggesting parental behavior to avoid a hospital visit. Differences were found in the percentage reduction among patients diagnosed with KD who were younger than 12 months vs 24 months or older.

Meaning  Findings of this study appear to support the hypothesis of a pathogenesis involving transmission of KD among children, especially among older children.


Importance  Global studies have reported that the incidence of Kawasaki disease (KD) declined during the COVID-19 pandemic. These studies suggest that the global pandemic and its accompanying mitigation measures may provide an important opportunity to explore the hypothesis of a KD pathogenesis.

Objective  To compare changes in KD incidence in Japan before and after the start of the COVID-19 pandemic.

Design, Setting, and Participants  This cohort study was conducted using the data set from Japan’s 26th nationwide KD survey that obtained information on patients who were diagnosed with KD in Japan from January 1, 2019, through December 31, 2020.

Main Outcomes and Measures  Kawasaki disease incidence rates were calculated by referring to the national population data in the vital statistics data for Japan.

Results  A total of 28 520 patients were identified (16 236 male individuals [56.9%]; median [IQR] age, 26 [14-44] months). A total of 17 347 patients were diagnosed with KD in 2019 and 11 173 were diagnosed in 2020, representing a 35.6% reduction in the number of patients diagnosed in 2020 compared with the previous year. Patient distributions for days of illness at the first hospital visit were almost identical in 2019 and 2020, suggesting that the decrease in KD incidence likely was not associated with pandemic-related delays in seeking treatment. The proportion of patients diagnosed with KD who were younger than 12 months was significantly larger in 2020 than in 2019 (21.6% vs 19.4%; P < .001). Compared with KD incidence among younger patients, the incidence among those 24 months and older declined rapidly after initiation of COVID-19 special mitigation measures, with a greater percentage reduction (58.3% reduction in July), but rebounded faster after the end of the special mitigation period. By contrast, the incidence among patients younger than 12 months declined moderately after the initiation of the special mitigation period, with a lower percentage reduction (40.3% reduction in October), and rebounded at a later phase.

Conclusions and Relevance  In this cohort study, the number of patients diagnosed with KD decreased by approximately one-third across Japan in 2020, with no indication that parents avoided a hospital visit. Differences in KD incidence reduction patterns before and after the initiation of COVID-19 pandemic mitigation measures were found in patients with KD aged younger than 12 months compared with those 24 months or older, suggesting a potential KD pathogenesis involving transmission among children.

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Article Information

Accepted for Publication: July 13, 2022.

Published Online: October 17, 2022. doi:10.1001/jamapediatrics.2022.3756

Correction: This article was corrected on December 5, 2022, to fix an error in Figure 1.

Corresponding Author: Ryusuke Ae, MD, PhD, Division of Public Health, Center for Community Medicine, Jichi Medical University, Yakushiji 3311-1, Shimotsuke, Tochigi 329-0498, Japan (shirouae@jichi.ac.jp).

Author Contributions: Dr Ae had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: Ae, Makino, Kuwabara, Kosami, Sasahara, Nakamura.

Acquisition, analysis, or interpretation of data: Ae, Makino, Kuwabara, Matsubara, Kosami, Nakamura.

Drafting of the manuscript: Ae, Matsubara, Nakamura.

Critical revision of the manuscript for important intellectual content: All authors.

Statistical analysis: Ae, Matsubara, Kosami, Nakamura.

Obtained funding: Nakamura.

Administrative, technical, or material support: Makino, Kuwabara, Nakamura.

Supervision: Makino, Kuwabara, Sasahara, Nakamura.

Conflict of Interest Disclosures: Dr Matsubara reported receiving grants from the Japan Kawasaki Disease Research Center during the conduct of the study. Dr Nakamura reported receiving grants from the Japan Kawasaki Disease Research Center during the conduct of the study. No other disclosures were reported.

Funding/Support: This study was supported by grants and funding from the Japan Kawasaki Disease Research Center (Dr Nakamura).

Role of the Funder/Sponsor: The funder had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Additional Contributions: We thank all the pediatricians who contributed to the nationwide KD survey in Japan. We also thank John Daniel of Edanz (https://jp.edanz.com/ac) for editing a draft of this manuscript. He did not receive compensation beyond his usual salary for his contribution to the article.

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