+SARS-CoV-2 infection in younger people often result in milder symptoms than infection in adults. However, a subset of children develop severe multisystem inflammatory symptoms associated with current or recent infection or contact exposures. These clinical findings have been grouped together in a condition known as multisystem inflammatory syndrome in children (MIS-C). Due to its relative recent introduction in scientific literature, epidemiological and demographic data on MIS-C is limited. This cohort study sought to estimate the population-based incidence of MIS-C per 1,000,000 person-months and incidence of MIS-C per 1,000,000 SARS-CoV-2 infections in people younger than 21 years from April to June 2020. Further stratification of cohorts was completed and classified via jurisdiction, race/ethnicity, sex, and age category. The main outcomes and measures of the analysis included overall and stratum-specific adjusted incidence of MIS-C per 1,000,000 person-months and per 1,000,000 SARS-CoV-2 infections. From 248 patients diagnosed with MIS-C included in the study, incidence was determined to be 5.1 persons per 1,000,000 person-months and 316 persons per 1,000,000 SARS-CoV-2 infections in people younger than 21 years. More specifically, incidence was found to be higher among ethnic minority groups including Black, Hispanic or Latino, and Asian or Pacific Islander compared to the White cohort and in younger individuals. These findings suggest that MIS-C remains a rare but serious complication associated with SARS-CoV-2 infection and further studies are required in order to determine and stratify risk factors for MIS-C. A limitation specific to this study was that in the event demographic information such as race/ethnicity was missing or identified as multiple or other in the database, a decision was made for it to be imputed based on the racial/ethnical distribution of the jurisdiction. This could have resulted in a high degree of variability among certain cohorts.
+This cohort study used enhanced surveillance data to identify children with MIS-C reported from 7 jurisdictions in the United States from April to June 2020. Denominators for population-based estimates were derived from updated census data and denominators for incidence among infected persons were estimated by applying known age- and month-specific multipliers, taking into account underdetection of reported COVID-19 cases. Jurisdictions included Connecticut, Georgia, Massachusetts, Michigan, New Jersey, New York (excluding New York City), and Pennsylvania and reporting was done through the Centers for Disease Control and Prevention and Overcoming COVID-19, a multicenter MIS-C clinical trial. From these 7 jurisdictions, 248 people with MIS-C were enrolled (median [IQR] age, 8 [4-13] years; 133 [53.6%] male; 96 persons [38.7%] were Hispanic or Latino; 75 persons [30.2%] were Black). Overall, the incidence of MIS-C per 1,000,000 person-months was 5.1 (95%CI, 4.5-5.8) persons. In comparison to the White cohort, incidence per 1,000,000 person-months was higher among Black (adjusted incidence rate ratio [aIRR], 9.26 [95%CI, 6.15-13.93]), Hispanic or Latino (aIRR, 8.92 [95%CI, 6.00-13.26]), and Asian or Pacific Islander peoples (aIRR, 2.94 [95%CI, 1.49-5.82]). Additionally, MIS-C incidence per 1,000,000 SARS-CoV-2 infections was 316 (95%CI, 278-357) persons and when compared to the White cohort at baseline, was higher in Black (aIRR, 5.62 [95%CI, 3.68-8.60]), Hispanic or Latino (aIRR, 4.26 [95%CI, 2.85-6.38]), and Asian or Pacific Islander cohorts (aIRR, 2.88 [95%CI, 1.42-5.83]). For both population-based and incidence among infected persons estimates, incidence was highest among children aged 5 years or younger (4.9 [95%CI, 3.7-6.6] children per 1,000,000 person-months) and children aged 6 to 10 years (6.3 [95%CI, 4.8-8.3] children per 1,000,000 person-months).