Incidence of Kawasaki disease before and during the COVID-19 pandemic: a retrospective cohort study in Japan

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.

Keywords: COVID-19; epidemiology; microbiology; rheumatology.

Figure 1

Monthly change of Kawasaki disease cases in 2016–2020.

Figure 2

Daily case numbers of COVID-19 in 2020. Orange and blue bars indicate individuals with <10 years and ≥10 years of age, respectively.

Figure 3

Bayesian time series plot of number of patients with KD aged 0–4 years in 2016–2020. The black line is the observed numbers of patients with KD aged 0–4, the red line is the predicted median, and the dark and light areas are 90% and 80% credible intervals, respectively. KD, Kawasaki disease.

Figure 4

Weekly case numbers of respiratory syncytial virus infection (A), influenza (B), group A streptococcal pharyngitis (C) and herpangina (D) among children aged 0–4 years in 2016–2020. Annual total number of each infection (A–D) was 96, 795, 279 and 94 in 2020, respectively, and 844, 2,460, 596 and 629 on average in the years 2016–2019, respectively. Cyan, orange, grey, yellow dotted lines and red solid lines indicate weekly changes in 2016, 2017, 2018, 2019 and 2020, respectively.