The SARS-CoV-2 viral load in COVID-19 patients is lower on face mask filters than on nasopharyngeal swabs

Agnieszka Smolinska 1,2, David S. Jessop 1, Kirk L. Pappan 1, Alexandra De Saedeleer 1, Amerjit Kang 1, Alexandra L. Martin 1, MaxAllsworth 1, CharlotteTyson 1, Martine P. Bos 3, Matt Clancy 3, Mike Morel 4, Tony Cooke 4, Tom Dymond 5, Claire Harris 6,7, JacquiGalloway 5, Paul Bresser 8, Nynke Dijkstra 8, Viresh Jagesar 8, Paul H. M. Savelkoul 9, ErikV. H. Beuken 9, Wesley H.V. Nix 9, Renaud Louis 10, Muriel Delvaux 10, Doriane Calmes 10, Benoit Ernst 10, Simona Pollini 11,12, Anna Peired 13, JulienGuiot 10, SaraTomassetti 11,14, Andries E. Budding 3, Frank McCaughan 6,7, Stefan J. Marciniak 6,7 & Marc P. van der Schee 1

1. Owlstone Medical Ltd., Cambridge, Cambridgeshire, UK. 2. Department of Pharmacology and Toxicology, Maastricht University, Maastricht, The Netherlands. 3. inBiome B.V., Amsterdam, The Netherlands. 4. Cambridge Clinical Laboratories Ltd., Cambridge, Cambridgeshire, UK. 5. Cambridge University Hospitals NHS Foundation Trust, Addenbrooke’s Hospital, Cambridge, UK. 6. Department of Medicine, Addenbrooke’s Hospital, Cambridge, UK. 7. University of Cambridge, Cambridge, UK. 8. Pulmonology, OLVG, Amsterdam, The Netherlands. 9. Department of Medical Microbiology, Maastricht University Medical Center, Care and Public Health Research Institute (Caphri), Maastricht, The Netherlands. 10. Repiratory Department, CHU Liège, Liège, Belgium. 11. Department of Experimental and Clinical Medicine, University of Florence, Florence, Italy. 12. Microbiology and Virology Unit, Careggi University Hospital, Florence, Italy. 13. Department of Experimental and Clinical Biomedical Sciences “Mario Serio”, University of Florence, Florence, Italy. 14. Interventional Pulmonology Unit, Careggi University Hospital, Florence, Italy.

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Face masks and personal respirators are used to curb the transmission of SARS-CoV-2 present in respiratory droplets; filters embedded in some personal protective equipment could be used as a non-invasive sample source for applications, including at-home testing, but information is needed about whether filters are suited to capture viral particles for SARS-CoV-2 detection. In this study, we generated inactivated virus-laden aerosols of 0.3–2 microns in diameter (0.9 µm mean diameter by mass) and dispersed the aerosolized viral particles onto electrostatic face mask filters. Using quantitative reverse transcription PCR, the limit of detection for inactivated coronaviruses SARS-CoV-2 and HCoV-NL63 extracted from filters was between 10 to 100 copies/filter for both viruses. Testing for SARS-CoV-2, using face mask filters and nasopharyngeal swabs collected from hospitalized COVID-19-patients, showed that filter samples offered reduced sensitivity (8.5% compared to nasopharyngeal swabs). The low concordance of SARS-CoV-2 detection between filters and nasopharyngeal swabs indicated that the number of viral particles collected on the face mask filter was below the limit of detection for all patients but those with the highest viral loads. This indicated face masks are unsuitable to replace diagnostic nasopharyngeal swabs for COVID-19 detection, but may have relevance in assessing transmissibility. Furthermore, the ability to detect nucleic acids on face mask filters may find other uses worthy of future investigation. 




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