Atypical activity of Respiratory Syncytial Virus during the COVID-19 pandemic in a Portuguese hospital

Introduction: Respiratory Syncytial Virus (RSV) represents the main cause of acute lower respiratory tract infection in children up to 5 years of age. After the COVID-19 pandemic started in 2020, it was necessary to implement control measures that also affected RSV activity. Objectives: Study the epidemiological profile of RSV in paediatric patients who attended Centro Hospitalar Póvoa de Varzim - Vila do Conde, from September 1, 2019, to March 31, 2022. Methodology: We studied the results of RSV screening by Polymerase Chain Reaction by consulting existing records in SISLAB®. Data analysis was performed in IBM SPSS Statistics 28. Results: The activity of RSV in the 2019/2020 season started on week 49 of 2019 and ended on week 11 of 2020. In the 2020/2021 season, there were no cases of infection. RSV activity was recorded from week 24 of 2021 until week 3 of 2022. Regarding RSV infection in children under 13 months, it represented 57.1% of infection cases, between 2019 and 2020, and 24.3% between 2021 and 2022. Conclusion: The absence of RSV activity coincided with the implementation of COVID-19 control measures. We registered an inter-seasonal outbreak of RSV after those control measures were relaxed, thus observing an RSV epidemiological profile different from that normally recorded in Portugal.