Multisystem Inflammatory Syndrome in Children and SARS-CoV-2 variants: a two-year ambispective multicentric cohort study in Catalonia, Spain.

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Abstract Purpose Multisystem inflammatory syndrome in children (MIS-C) is a rare but severe disease temporarily related to SARS-CoV-2. We aimed to describe the epidemiological, clinical and laboratory findings of all the MIS-C cases diagnosed in children < 18 years-old in Catalonia (Spain) to study their trend throughout the pandemic. Methods Multicenter ambispective observational cohort study (April 2020-April 2022). Data were obtained from the COVID-19 Catalan surveillance system and from all the hospitals in Catalonia. We analyzed MIS-C cases regarding SARS-CoV-2 variants for demographics, symptoms, severity, monthly MIS-C incidence, ratio between MIS-C and accumulated COVID-19 cases, and associated rate ratios (RR). Results Among 555,848 SARS-CoV-2 infections, 152 children were diagnosed with MIS-C. Monthly MIS-C incidence was 4.1 (95%CI: 3.4–4.8) per 1,000,000 people, and 273 (95%CI: 230–316) per 1,000,000 SARS-CoV-2 infections (i.e., one case per 3,700 SARS-CoV-2 infections). During the Omicron period, MIS-C RR was 8.2 (95%CI: 5.7–11.7) per 1,000,000 SARS-CoV-2 infections, significantly lower (p < 0.001) than for previous variant periods, in all age groups. Median [IQR] age of MIS-C was 8 [4–11] years, 62.5% male, and 80.2% without comorbidities. Common symptoms were gastrointestinal findings (88.2%) and fever > 39oC (81.6%), nearly 40% had an abnormal echocardiography and 7% coronary aneurysm. Clinical manifestations and laboratory data were not different throughout the variant periods (p > 0.05). Conclusions The rate ratio between MIS-C cases and SARS-CoV-2 infections was significantly lower in the Omicron period for all the age groups, including those not vaccinated, suggesting that the variant could be the main factor for this shift in the MISC trend. Regardless of variant type, the patients had similar phenotypes and severity throughout the pandemic.

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