Post-pandemic resurgence and co-detectiondynamics of respiratory pathogens revealed by syndromic multiplex PCR

Acute respiratory tract infections are a major cause of morbidity and healthcare burden worldwide. Because many respiratory pathogens such as influenza viruses, Respiratory Syncytial Virus (RSV), Rhinovirus/Enterovirus, and SARS-CoV-2 present with overlapping clinical features, rapid and accurate etiological diagnosis is essential for effective patient management. Syndromic multiplex PCR panels, particularly the BioFire FilmArray Respiratory Panel 2.1 Plus (RP2.1 Plus), enable the simultaneous detection of a broad range of viral and bacterial pathogens, facilitating the identification of both mono- and co-infections. This study aimed to investigate the distribution of respiratory pathogens, co-detectionpatterns, seasonal variation, and sequential infections in patients with suspected respiratory tract infections using BioFire RP2.1 Plus in a tertiary-care hospital in Türkiye. In this retrospective observational study, 360 respiratory samples obtained from 314 patients between March 2024 and March 2025 were analysed. All samples were tested using the BioFire FilmArray RP2.1 Plus system. Pathogen frequencies, mono- and co-detectionrates, demographic associations, seasonal distribution, and correlations between circulating pathogens were evaluated using appropriate statistical methods. At least one respiratory pathogen was detected in 55.8% (201/360) of samples. A total of 253 pathogens were identified. The most frequent pathogen was Rhinovirus/Enterovirus (38.7%), followed by influenza A (12.3%), adenovirus (10.7%), SARS-CoV-2 (7.9%), RSV (6.3%), and Mycoplasma pneumoniae (4.3%). Co-detections were identified in 20.4% of positive samples, with binary co-infections being the most common. Rhinovirus/Enterovirus was the dominant pathogen in all co-detectioncategories. Women and children had significantly higher positivity rates than men and adults, respectively. Marked seasonal variation was observed: influenza A, RSV, human metapneumovirus, adenovirus, and M. pneumoniae were predominantly detected during the cold season (October–March), while Rhinovirus/Enterovirus circulated throughout the year. A strong positive correlation was observed between RSV and influenza A (ρ = 0.68, p = 0.011). Sequential sample analysis suggested that many co-detections may reflect sequential rather than simultaneous infections, potentially representing residual nucleic acid from recent infections. Real-life BioFire RP2.1 Plus testing demonstrated high etiological diversity, frequent co-detections, and pronounced seasonal dynamics of respiratory pathogens in the post-pandemic period, confirming the clinical and epidemiological value of syndromic multiplex PCR–based respiratory diagnostics.