Abstract
BACKGROUND: Multisystem inflammatory syndrome in children (MIS-C) is a rare but serious complication after coronavirus disease 2019. In South Korea, the Korea Disease Control and Prevention Agency has conducted national surveillance of MIS-C from May 2020 to March 2023. This project was carried out during the second phase of the surveillance, which included enhancements to the reporting system starting in August 2022. In addition to monitoring the epidemiological and clinical characteristics, we analyzed cytokine changes and genetic factors. METHODS: A user-friendly web-based reporting system using an electronic case report form (e-CRF) was established to provide clinicians in the field with easy access to reports. Cases collected from August 2022 to March 2023 were evaluated to confirm diagnoses, and unclassified cases from the prior research period were also reviewed. For patients who provided consent, serum cytokine measurements and whole-genome sequence analyses were conducted. RESULTS: In this study, 55 cases were confirmed as MIS-C. Of the 32 cases reported via e-CRF in the second period, 28 were confirmed as MIS-C. Among 31 cases reported but unclassified in the first period, 27 were subsequently confirmed as MIS-C. The median patient age was 7.8 years (range: 2 months to 16 years), with 54.5% (30/55) male. Clinically, 15 patients (27%) had abnormal echocardiography findings, and 5 (9.1%) required intensive care unit care. Steroids were administered to 45 patients (81.8%) and intravenous immunoglobulin to 46 (83.6%). No mortality occurred. In two patients, 17 serum cytokines were measured pre- and post-treatment, with interleukin (IL)-6, IL-17/IL-17A, IL-1ra/IL-1F3, IL-10, and CXC motif chemokine ligand 10 (CXCL10)/inducible protein 10 kDa (IP-10) peaking before treatment and decreasing afterward. Whole-genome sequencing in 6 patients revealed no previously reported MIS-C-associated genetic variants. CONCLUSION: Continuous monitoring of MIS-C cases is essential, as some may develop serious complications. Clinicians should remain vigilant in diagnosing MIS-C, and further research is needed to elucidate its pathogenesis.