Infectious Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Exhaled Aerosols and Efficacy of Masks During Early Mild Infection

• Published in: Clinical infectious diseases 2022-08, Vol.75 (1), p.e241-e248
• Main Authors: Adenaiye, Oluwasanmi O, Lai, Jianyu, Bueno de Mesquita, P Jacob, Hong, Filbert, Youssefi, Somayeh, German, Jennifer, Tai, S H Sheldon, Albert, Barbara, Schanz, Maria, Weston, Stuart, Hang, Jun, Fung, Christian, Chung, Hye Kyung, Coleman, Kristen K, Sapoval, Nicolae, Treangen, Todd, Berry, Irina Maljkovic, Mullins, Kristin, Frieman, Matthew, Ma, Tianzhou, Milton, Donald K
• Format: Article
• Language: English
• Subjects: COVID-19 - prevention & control; Humans; Major; Masks; Respiratory Aerosols and Droplets; RNA, Viral; SARS-CoV-2
• ISSN: 1058-4838; 1537-6591
• DOI: 10.1093/cid/ciab797

Abstract Background Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) epidemiology implicates airborne transmission; aerosol infectiousness and impacts of masks and variants on aerosol shedding are not well understood. Methods We recruited coronavirus disease 2019 (COVID-19) cases to give blood, saliva, mid-turbinate and fomite (phone) swabs, and 30-minute breath samples while vocalizing into a Gesundheit-II, with and without masks at up to 2 visits 2 days apart. We quantified and sequenced viral RNA, cultured virus, and assayed serum samples for anti-spike and anti-receptor binding domain antibodies. Results We enrolled 49 seronegative cases (mean days post onset 3.8 ± 2.1), May 2020 through April 2021. We detected SARS-CoV-2 RNA in 36% of fine (≤5 µm), 26% of coarse (>5 µm) aerosols, and 52% of fomite samples overall and in all samples from 4 alpha variant cases. Masks reduced viral RNA by 48% (95% confidence interval [CI], 3 to 72%) in fine and by 77% (95% CI, 51 to 89%) in coarse aerosols; cloth and surgical masks were not significantly different. The alpha variant was associated with a 43-fold (95% CI, 6.6- to 280-fold) increase in fine aerosol viral RNA, compared with earlier viruses, that remained a significant 18-fold (95% CI, 3.4- to 92-fold) increase adjusting for viral RNA in saliva, swabs, and other potential confounders. Two fine aerosol samples, collected while participants wore masks, were culture-positive. Conclusions SARS-CoV-2 is evolving toward more efficient aerosol generation and loose-fitting masks provide significant but only modest source control. Therefore, until vaccination rates are very high, continued layered controls and tight-fitting masks and respirators will be necessary. Exhaled SARS-CoV-2 aerosols are infectious and evolution is favoring more efficient aerosol generation. Loose-fitting masks moderately reduce viral aerosol release indicating that ventilation, filtration, UV air sanitation, and tight-fitting masks are needed to protect vulnerable people in public-facing jobs and indoor spaces.