Clinical course and seroprevalence of COVID-19 in children with rheumatic diseases. Cross-sectional study from a reference centre in Spain.

Abstract Background Patients with rheumatic diseases have been considered at risk of COVID-19. A significant percentage of infections in children are asymptomatic or mild and can go unnoticed. This study aims to describe the seroprevalence of SARS-CoV-2 in a cohort of children with rheumatic diseases and assess possible risk factors. Methods: A cross-sectional study was performed in a pediatric rheumatology unit from a reference hospital in Madrid, from September 2020 to February 2021. Serology of SARS-CoV-2 was performed at the same time as their routine laboratory tests, and a specific questionnaire was completed by parents. Demographics, treatment and disease activity from laboratory-confirmed COVID-19 patients were compared to the data of patients without laboratory-confirmed COVID-19.Findings A total of 105 children were included. SARS-CoV-2 infection was demonstrated in 27 patients (25.7%): 6 PCR and 21 positive IgG serology. The mean age was 11.8 years , and the majority of the patients were females (72.4%). Most of the children were diagnosed with juvenile idiopathic arthritis (JIA) (70.3%; 19/27), followed by PFAPA (11.1%; 3/27). Immunosuppresive treatment was given in 88% of cases (24/27). Overall, 44.4% (12/27) of infected patients were asymptomatic. Three patients required hospital admission because of COVID-19, however none of them required oxygen supplementation. A total of 66.7% (18/27) of patients did not require any treatment or medical assistance. The seroprevalence in our cohort was 20% in contrast to the 7.7% population seroprevalence observed during the same study period in Spanish children. SARS-CoV-2 confirmed children with positive IgG or PCR were less frequently in remission (52% vs 72%; p 0.014). Moderate disease activity and treatment with oral corticosteroids were associated with higher risk for COVID-19 (OR 5.05; CI 95%: 1.56 - 16.3 and OR 4.2; CI 95%: 1.26 - 13.9 respectively). Conclusions In a cohort of pediatric patients with rheumatic disease and immunosuppressive therapy, moderate disease activity and oral corticosteroids were associated with COVID-19 positive patients. Seroprevalence was significantly higher compared to the same age healthy population. The clinical manifestations were mild and there were no severe infections among the patients.