Stable Kawasaki disease incidence during COVID-19 quarantine suggests airborne transmission
Despite COVID-19 quarantine measures, Kawasaki disease incidence was unchanged in Japan compared with significant declines in respiratory tract and gastrointestinal infections, indicating airborne rather than contact or droplet transmission.
“Despite long-term active research, the triggers for [Kawasaki disease (KD)] remain unknown,” Takuya Hara, MD, of Fukuoka Children’s Hospital, in Japan, and colleagues wrote in JAMA Network Open. “One dominant theory is that KD arises after infection, particularly by pathogens transmitted via contact or droplets. However, controversy remains regarding whether the major trigger is infectious, whether it is single or multiple, and how the transmission occurs.”
“In Japan, the first SARS-CoV-2 outbreaks occurred in February 2020,” they added. “Under these conditions, handwashing, masks and physical distancing were urged, and the government declared a COVID-19 state of emergency, which lasted from April 7 to May 25, 2020. Consequently, the chances of exposure to not only SARS-CoV-2 but also other pathogens that can be spread by contact or droplets were decreased. To our knowledge, no data are currently available for the preventive effect of the nationwide quarantine on the occurrence of KD during the COVID-19 pandemic.”
To examine the role of droplet or contact transmission in the development of Kawasaki disease, Hara and colleagues conducted a multicenter, longitudinal, cross-sectional study of patients at Fukuoka Children’s Hospital and five other adjacent general hospitals. The researchers analyzed the number of admissions for Kawasaki disease and infectious diseases from 2015 to 2020 — before and after the introduction of COVID-19-related emergency health measures. In all, they included 1,649 pediatric participants with Kawasaki disease and 15,586 with infectious disease.
For their primary outcome, Hara and colleagues compared the ratios of patients with Kawasaki disease to those with respiratory tract or gastrointestinal infections, admitted from April to May in 2015 as well as from 2019 and 2020. Their analysis included a Poisson regression mode.
According to the researchers, there was no significant change in the number of Kawasaki disease admissions between April and May in 2015 to 2019, compared with the same months in 2020. In all, the researchers observed a 27.4% decrease, with an adjusted incidence rate ratio of 0.73 (95% CI, 0.48-1.1). However, the number of admissions for droplet- or contact-transmitted respiratory tract and gastrointestinal infections decreased 75.3% (aIRR = 0.25; 95% CI, 0.17-0.35) and 86.3% (aIRR = 0.14; 95% CI, 0.04-0.43), respectively.
As such, the ratio of Kawasaki disease incidence to that of droplet- or contact-transmitted respiratory tract and gastrointestinal infections in April and May 2020 was significantly increased, at 0.4 compared with 0.12 (P < .001).
“The ratio of KD to droplet- or contact-transmitted respiratory tract and gastrointestinal infections during the COVID-19 state of emergency in April to May 2020 was significantly increased because of the large decrease in the two infections and the smaller decrease in KD,” Hara and colleagues wrote. “Furthermore, the number of KD cases remained significantly lower from shortly after this period.”
“These findings suggest that transmission by contact or droplets is not a major route for KD development in Japan and support the findings of previous epidemiological studies indicating that KD may be associated with airborne disease in most cases,” they added. “More extensive studies are warranted for further understanding of this intriguing disease.”