Size, cytopathic effects, and prevalence of Influenza, SARS-CoV-2, and RSV in healthcare settings

Airborne transmission of respiratory viruses in healthcare settings is difficult to assess, particularly with respect to the size and viability of virus-containing aerosols. Most field studies rely on molecular detection, which limits inference about the infectiousness of virus. In this study we collected size-resolved airborne samples in a dental clinic and hospital during the 2024-2025 respiratory virus season using a BC (BioCascade)-BioSpot VIVAS (Viable Virus Aerosol Sampler). We analyzed these samples by RT-PCR and culture-based assays for influenza A, influenza B, SARS-CoV-2, and respiratory syncytial virus (RSV). Viral RNA was detected in 11.1% of the 81 sampling events, with the highest positivity (25%) observed in pulmonary unit patient rooms. When influenza and SARS-CoV-2 RNA were detected, all of these detections occurred in the 4-10 μm size fraction, whereas all RSV RNA was detected in the <1.5 μm size fraction. Cell culture assays confirmed the presence of viable influenza in the samples that were positive by RT-PCR. Plaques were only observed for influenza A viral positive samples at the ‘neat’ or undiluted rate, whereas RSV and SARS-CoV-2 did not produce cytopathic effects in the cell culture assays. These findings highlight virus-specific differences in aerosol size distributions and the challenges of recovering viable virus from field-collected bioaerosols in healthcare environments.