Detection of SARS-CoV-2 RNA on air purifier filters in university spaces without symptomatic or confirmed cases

Understanding the seasonality and prevalence of respiratory viruses in indoor environments is essential for protecting public health in the post-pandemic era. This study investigated the presence of airborne SARS-CoV-2 in university indoor spaces where no symptomatic or confirmed positive individuals were supposed to be present. A total of 127 high-efficiency particulate air (HEPA) filter samples were analyzed from air purifiers installed in classrooms, conference rooms, and a community room within a university building across different seasons from Fall 2022 to Summer 2023. Viral RNA was extracted and quantified using RT-qPCR for each sample. SARS-CoV-2 RNA was detected in 21% of the samples, with the positivity rate varying significantly by room type but not by season. Among the 27 positive samples, viral RNA concentrations were significantly higher in fall-winter compared to summer, with no significant differences across room types. Additionally, respiratory syncytial virus (RSV) and influenza A virus (IAV) were detected in far fewer samples (positive rates: 2% and 4%, respectively) and at much lower concentrations than SARS-CoV-2. These findings provide evidence of the potential for airborne SARS-CoV-2 transmission in shared indoor spaces, even in the absence of known infectious individuals. They also suggest that SARS-CoV-2 may circulate in each season, underscoring the continued need for interventions to reduce indoor viral exposure.