Multi-inflammatory syndrome in children (MIS-C) was found to be a rare complication of SARS-CoV-2 infection, with a decreased occurrence of Kawasaki disease observed during the COVID-19 pandemic, according to study results published in Acta Paediatrica.
In a nationwide, register-based study in Finland, researchers sought to explore the epidemiology of Kawasaki disease and MIS-C relative to the ongoing COVID-19 pandemic. The current study was based on cases of laboratory-confirmed SARS-CoV-2 infections, Kawasaki disease, and MIS-C. A time series analysis was performed with regard to the occurrence of Kawasaki disease between 2016 and 2020, as well as MIS-C in 2020. Finland recommends free SARS-CoV-2 polymerase chain reaction (PCR) testing for all children who present with any symptoms indicative of COVID-19, even those with mild symptoms.
A total of 5170 PCR-confirmed COVID-19 cases were reported among Finnish children younger than 18 years in 2020. The incidence of SARS-CoV-2 infection in this population was 470 per 100,000 persons (95% CI, 457-483 per 100,00 persons), among whom 5 fulfilled the case definition for MIS-C (from March 1 to December 31, 2020). No deaths were reported among these patients. In addition, the annual population-based incidence of MIS-C was 0.45 per 100,000 children (95% CI, 0.15-1.06 per 100,000 children) younger than 18 years. When the rate of MIS-C was calculated against all PCR-confirmed cases of SARS-CoV-2 infections in this pediatric population, the occurrence of MIS-C was 0.97 per 1000 individuals (95% CI, 0.31-2.26 per 1000 individuals).
In 2020, the population-based incidence rate of Kawasaki disease among children was 4.6 per 100,000 persons (95% CI, 3.5-6.1 per 100,000 persons). For quarterly time periods between 2016 and 2020, the incidence ranged from 2.18 (95% CI, 1.40-3.25) between January and March 2018 to 0.55 (95% CI, 0.20-1.19) between July and September 2020, as well as between October and December 2020.
Based on the results of the time series analysis, the occurrence of Kawasaki disease decreased during vs before the COVID-19 pandemic, with an incidence rate ratio of 0.49 (95% CI, 0.29-0.72). In children and adolescents aged between 0 and 19 years, the occurrence of influenza A, respiratory syncytial virus, Streptococcus pneumoniae, and Mycoplasma pneumoniae decreased markedly after March 2020, possibly because of school closures in Finland during the pandemic.
Researchers concluded that transmissible microbes may play an important role in the pathogenesis of Kawasaki disease and that practicing social distancing may have a protective effect.
Koskela U, Helve O, Sarvikivi E, et al. Multi-inflammatory syndrome and Kawasaki disease in children during the COVID-19 pandemic: a nationwide register-based study and time series analysis. Acta Paediatr. Published online July 31, 2021. doi:10.1111/apa.16051