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Detection of Non-infectious SARS-CoV-2 from Aggregated Samples of Bioaerosols Produced during Expiratory Activities
Tyler J. Johnson, ROBERT T. NISHIDA, Ashlesha P. Sonpar, James Lin, Kimberley Watson, Stephanie Smith, John Conly, David Evans, Jason S. Olfert, University of Alberta
Abstract Number: 588
Working Group: Infectious Aerosols in the Age of COVID-19
Abstract
The COVID-19 pandemic is caused by transmission of SARS-CoV-2 from person-to-person. At the time of writing, SARS-CoV-2 RNA has been detected in samples of ambient air and surfaces in clinical settings, including in aerosols smaller than 5 μm in diameter, likely produced by patients nearby. The limited number of studies to date which include samples of air directly exhaled by study participants have not reported attempts to culture the virus. In this work, participants identified by a recent positive oro- or naso-pharyngeal (NP) swab were asked to breathe, speak and cough into a single-use, medical-grade mask placed directly over their nose and mouth and the bioaerosols they emitted were continuously sampled from air in the mask by bioaerosol samplers (i.e. BioSampler® and Andersen Cascade Impactor) for ex situ virological analyses. Cycle thresholds (Ct) from quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR) analyses indicate RNA of SARS-CoV-2 was present in samples of air emitted by participants (in aggregate samples of breathing, speaking and coughing), including in bioaerosols smaller than 10 μm in aerodynamic diameter. Despite detecting SARS-CoV-2 RNA in air samples (e.g. from BioSampler, n=17; Ct: 26.4-36.6), previous data shows those samples were unlikely to culture. Indeed, all attempts to culture the virus from samples of bioaerosols have been negative to date (0 of 27; limit of detection, 5 PFU/mL) despite sampling air directly emitted by participants who carried infectious virus as detected by viral culture of their NP swab (positive by plaque assay: 53%, 9 of 17, Titer: 15 PFU/mL - 18,000 PFU/mL; positive by RT-qPCR: 100%, 17 of 17, Ct: 16.2-30.3).