Unusual trend of respiratory syncytial virus burden of disease observed in primary care diagnosis of children under 5 years old in Catalonia during the COVID-19 pandemic

Background Great reductions of respiratory syncytial virus (RSV) in children were observed during the 2020 Southern hemisphere winter. Aim To describe trends of RSV related disease in children in the Northern hemisphere and to propose a low cost clinical surveillance system based on primary care electronic health records (EHR). Methods Time series analysis of RSV-related disease and virus laboratory-confirmations in children under 5 years old from 1 September 2009 to 16 January 2021. We collected RSV diagnoses from primary care EHR in Catalonia (Spain). We compared the trend of RSV in the season 2020-2021 with that in the previous seasons. We estimated the expected RSV cases with data from 2009 to 2018 using a time series regression adjusted by seasonality. We used the same method to estimate the expected RSV laboratory-confirmations as a sensitivity analysis. Results In previous seasons, RSV-related disease peaks in Catalonia during the weeks 52 and 53. However in the 2020-2021 period, we observed a reduction of 87.6% (95% CI: 82.7% to 90.3%) in RSV-related disease from october 2020 compared to the expected. Only 1 RSV case was laboratory-confirmed during the 2020-2021 season until mid-January. Conclusions We observed a nearly absence of RSV-related disease and laboratory-confirmations during the weeks when RSV usually peaks in Catalonia. The use of primary care EHR could be a low-cost surveillance system to monitorize trends of RSV the coming months.