Nationwide Survey of Multisystem Inflammatory Syndrome in Children Associated with Coronavirus Disease 2019 in Japan.

BACKGROUND

Multisystem inflammatory syndrome in children (MIS-C) presents some clinical overlap with Kawasaki disease (KD). Although KD is common in Japan, the clinical characteristics of MIS-C in Japan remain unknown. Therefore, we aimed to determine the epidemiological and clinical features of MIS-C in Japan.

METHODS

Using a case reporting form, a nationwide registry was created between November 2020 and March 2023, involving 2,080 facilities throughout Japan. We prospectively and retrospectively enrolled patients with MIS-C. The primary outcomes were the number and incidence rates of children with MIS-C. The secondary outcomes included clinical features, such as KD phenotype, organ involvement, shock, intensive care unit admission, and coronary artery lesions.

RESULTS

Among 398 patients registered, central review identified 129 MIS-C cases (mean age: 8·8 ± 3·7 years). The overall incidence rate was estimated to be 1·5 per 100,000 COVID-19 cases, exhibiting a decline as the COVID-19 pandemic progressed, from 12·3 cases (Pre-Delta) to 1·3 cases (Omicron); 80% of MIS-C cases occurred during the Omicron variant predominant period, and 72% of children with MIS-C met the KD criteria. Cardiovascular (88%) and gastrointestinal (90%) involvement were frequent. In Japan, MIS-C cases showed comparatively less severe clinical features, with shock in 29% and admission to the intensive care unit in 12% of cases. Coronary artery lesions were identified in 15 cases (11·6%), irrespective of the presence of shock. No fatalities were reported.

CONCLUSION

The incidence of MIS-C was low in Japan. The clinical features distinctively exhibited a more KD-like phenotype, with less severe clinical features.