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Epidemiology
Original research
Incidence of Kawasaki disease before and during the COVID-19 pandemic: a retrospective cohort study in Japan
  1. Kyohei Iio1,
  2. Kousaku Matsubara1,
  3. Chisato Miyakoshi2,
  4. Kunitaka Ota3,
  5. Rika Yamaoka4,
  6. Junji Eguchi5,
  7. Osamu Matsumura6,
  8. Takahiro Okutani7,
  9. Ikuyo Ueda8,
  10. Masahiro Nishiyama9
  1. 1Department of Pediatrics, Kobe City Nishi-Kobe Medical Center, Kobe, Hyogo, Japan
  2. 2Department of Pediatrics, Kobe City Medical Center General Hospital, Kobe, Hyogo, Japan
  3. 3Department of Pediatrics, Konan Medical Center, Kobe, Hyogo, Japan
  4. 4Department of Pediatrics, National Hospital Organization Kobe Medical Center, Kobe, Hyogo, Japan
  5. 5Department of Pediatrics, Kobe City Medical Center West Hospital, Kobe, Hyogo, Japan
  6. 6Department of General Pediatrics, Hyogo Prefectural Kobe Children’s Hospital, Kobe, Hyogo, Japan
  7. 7Department of Pediatrics, Saiseikai Hyogo-ken Hospital, Kobe, Hyogo, Japan
  8. 8Department of Pediatrics, Japan Community Health Care Organization Kobe Central Hospital, Kobe, Hyogo, Japan
  9. 9Department of Pediatrics, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan
  1. Correspondence to Dr Kousaku Matsubara; kskmatsu{at}s4.dion.ne.jp

Abstract

Background Epidemiological studies in Kawasaki disease (KD) have suggested infectious aetiology. During the COVID-19 pandemic, measures for mitigating SARS-CoV-2 transmission also suppress the circulation of other contagious microorganisms. The primary objective is to compare the number and incidence of KD before and during the COVID-19 pandemic in Japan, and the secondary objective is to investigate temporal association between the KD epidemiology and activities of SARS-CoV-2 and other viral and bacterial infections.

Methods A retrospective cohort study was conducted between 2016 and 2020 in Kobe, Japan. We collected information of hospitalised KD children in Kobe. Child population was identified through the resident registry system. Activity of COVID-19 and 11 other infectious diseases was derived from a public health monitoring system. Monthly change of KD incidence was analysed using a difference-in-difference regression model.

Results Throughout the study period, 1027 KD children were identified. KD had begun to decline in April 2020, coinciding with the beginning of the COVID-19 pandemic. The number of KD cases (n=66) between April and December 2020 was 40% of the average in the same period in 2016–2019 (165/year). Annual KD incidence was 315, 300, 353, 347 and 188/100 000 children aged 0–4 years in 2016–2020, respectively. The difference-in-difference value of KD incidence was significantly reduced in the fourth quarter in 2020 (−15.8, 95% CI −28.0 to −3.5), compared with that in 2016–2019. Sentinel surveillance showed a marked decrease of all infectious diseases except exanthema subitum after the beginning of the COVID-19 pandemic. There were 86 COVID-19 cases aged <10 years and no KD children associated with COVID-19.

Conclusion This study showed that the number and incidence of KD was dramatically reduced during the COVID-19 pandemic in Japan. This change was temporally associated with decreased activities of various infectious diseases other than COVID-19, supporting the hypothesis of infection-triggered pathogenesis in KD.

  • COVID-19
  • epidemiology
  • microbiology
  • rheumatology

Data availability statement

Data are available on reasonable request. KI and KM had full access to the data in the study and take responsibility for the accuracy and integrity of the data. Data are available on reasonable request.

http://creativecommons.org/licenses/by-nc/4.0/

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

https://doi.org/10.1136/bmjpo-2021-001034

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    Data availability statement

    Data are available on reasonable request. KI and KM had full access to the data in the study and take responsibility for the accuracy and integrity of the data. Data are available on reasonable request.

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    Footnotes

    • Contributors KM and CM conceptualised and designed the study. KI, KM and CM drafted the manuscript. CM carried out statistical analyses. All authors collected the data and critically reviewed the manuscript. All authors read and approved the final manuscript as submitted.

    • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

    • Competing interests None declared.

    • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

    • Provenance and peer review Not commissioned; externally peer reviewed.