Reduction of respiratory syncytial virus burden of disease observed in primary care diagnosis of children under 5 years old during the COVID-19 pandemic: a time-series analysis using routinely collected data from primary care electronic health records in Catalonia (Spain).

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.