Epidemiology of respiratory viruses before and during the COVID-19 pandemic in a tertiary care hospital in Southern Brazil

• Each respiratory virus presents a distinct pattern of behavior and viral seasonality is variable. • The pandemic context lead to changes in the dynamics of respiratory infections. • Respiratory viruses have been contained due to measures in response to the pandemic. • The importance of monitoring and surveillance of respiratory viruses is even clearer. Respiratory viral infections affect millions of people worldwide and are life threatening for many of them. The viral seasonality leads to changes in the dynamics of respiratory infections and the importance of monitoring and surveillance of respiratory viruses becomes clearer. This study aims to analyze data from respiratory virus testing at the Hospital de Clínicas de Porto Alegre (HCPA) to evaluate their epidemiology from 2018 to 2021, observing their occurrence and seasonality before and after the onset of the SARS-CoV-2 pandemic. In this study, data analysis was divided into four time periods, corresponding to 2018 to 2021. Anonymized patients diagnosed with influenza virus (FLU), human parainfluenza virus (HPIV), human respiratory syncytial virus (HRSV), SARS-CoV-2 virus, or human adenovirus (HAdV) were included. We conducted chi-square goodness-of-fit tests for each virus by year, and a p-value of <0.05 was considered statistically significant. All analyzed respiratory viruses presented reduced case numbers during the COVID-19 pandemic, except FLU, which showed an increase of four cases in 2021 compared to 2019. For most viruses, the lowest incidence of confirmed cases was found in 2020. Furthermore, when excluding SARS-CoV-2, HRSV presented the most positive cases during the studied period, except in 2020. Besides SARS-CoV-2, the FLU was the only other respiratory virus that recorded deaths. It was also possible to observe that the number of SARS-CoV-2 cases reduced from April 2021. We observed that most respiratory tract viral infections decreased during the COVID-19 pandemic, and this result may be associated with the public interventions for containing the COVID-19 pandemic. Moreover, the reduction of these other viruses may have resulted from the measures for prevention conducted by HCPA.