Epidemiology and molecular characterization of respiratory viruses at the end of COVID-19 pandemic in Lombardy, Northern Italy.

The COVID-19 pandemic forced the adoption of non-pharmaceutical interventions (NPIs) which influenced the circulation of other respiratory pathogens, such as Influenza virus (FLU), Parainfluenza virus (PIV), Respiratory Syncytial virus (RSV), Rhinovirus (RV), Enterovirus (EV), Adenovirus (AdV), Human Metapneumovirus (hMPV), and Human Coronavirus (CoV). The aim of the current study was to investigate how, with the end of the pandemic, the withdrawal of the NPIs impacted on the circulation and distribution of common respiratory viruses. The analyzed samples were collected from June 2021 to March 2023 (post-pandemic period) and compared to ones from the pandemic period. Nucleic acid detection of all respiratory viruses was performed by multiplex real time Polymerase Chain Reaction (PCR) and sequencing was conducted by Next Generation Sequencing (NGS) technique. Our analysis shows that the NPIs adopted against SARS-CoV-2 were also effective in controlling the spread of other respiratory viruses. Moreover, we documented how RV/EVs were the most commonly identified species, with the more abundant strains represented by Coxsackievirus (CV)-A/B and RV-A/C. RV/EVs were also detected in some co-infection cases; in particular, the majority of co-infections concerned CV-B/RV-A, CV-B/ECHO. Given the pandemic potential of respiratory viruses, accurate molecular screening is essential for a proper surveillance and prevention strategy.