Molecular Surveillance of Respiratory Viral Pathogens Detected by Multiplex PCR During the Post-COVID-19 Period: Distribution, Co-infections, and Seasonal Patterns.

BACKGROUND: The COVID-19 pandemic profoundly altered the circulation dynamics of respiratory viruses worldwide. However, data describing post-COVID-19 viral epidemiology remain limited. This study aimed to characterize the distribution, demographic associations, co-infection patterns, and seasonality of respiratory pathogens detected by multiplex PCR in the post-COVID-19 period. METHODS: In this retrospective single-center study, 750 patients whose respiratory tract specimens were submitted to a tertiary care university hospital between February 2023 and March 2024 were included. Samples were analyzed using the BioFire FilmArray Respiratory Panel 2.1 Plus. Associations between categorical variables were evaluated using Pearson's chi-square or Fisher's exact test. RESULTS: At least one pathogen was detected in 56.3% (422/750) of patients. Of 535 detected pathogens, 98.5% were viral agents. Human rhinovirus/enterovirus (30.3%) was the most frequently identified virus overall and predominated in pediatric patients (43.4%), whereas SARS-CoV-2 was most common among adults (22.9%). Influenza viruses (17.4%) and respiratory syncytial virus demonstrated marked winter predominance, while human rhinovirus/enterovirus and SARS-CoV-2 circulated year-round. Overall positivity and co-infection rates were significantly higher in pediatric patients (p<0.001). Co-infections were detected in 22.3% of positive cases. Significant associations were observed between viral distribution and age group, gender, hospitalization status, and season (p<0.05). CONCLUSIONS: Respiratory viruses continue to dominate the etiology of acute respiratory tract infections in the post-COVID-19 era, with distinct age-related patterns and sustained circulation of SARS-CoV-2. Multiplex PCR-based molecular surveillance provides essential insights into evolving viral epidemiology and supports ongoing monitoring of respiratory virus dynamics.