Evolution of SARS-CoV-2 Shedding in Exhaled Breath Aerosols

Aerosol inhalation is increasingly well recognized as a major if not primary mode of transmission of SARS-CoV-21,2. Over the course of the COVID-19 pandemic, three highly transmissible lineages evolved and became globally dominant3. One hypothesis to explain increased transmissibility is that natural selection favours variants with higher rates of viral aerosol shedding. However, the extent of aerosol shedding of successive SARS-CoV-2 variants is unknown. Here, we demonstrate that viral shedding (measured as RNA copies) into exhaled breath aerosol was significantly greater during infections with Alpha, Delta, and Omicron than with ancestral strains and variants not associated with increased transmissibility. The three highly transmissible variants independently evolved a high viral aerosol shedding phenotype, demonstrating convergent evolution. We did not observe statistically significant differences in rates of shedding between Alpha, Delta, and Omicron infections. The highest shedder in our study, however, had an Omicron infection and shed three orders of magnitude more viral RNA copies than the maximum observed for Delta and Alpha4. Our results also show that fully vaccinated and boosted individuals, when infected, can shed infectious SARS-CoV-2 via exhaled breath aerosols. These findings provide additional evidence that inhalation of infectious aerosols is the dominant mode of transmission and emphasize the importance of ventilation, filtration, and air disinfection to mitigate the pandemic and protect vulnerable populations. We anticipate that monitoring aerosol shedding from new SARS-CoV-2 variants and emerging pathogens will be an important component of future threat assessments and will help guide interventions to prevent transmission via inhalation exposure.

Transmission modes of severe acute respiratory syndrome coronavirus 2 and implications for infection control: a review

The complete picture regarding transmission modes of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is unknown. This review summarises the available evidence on its transmission modes, our preliminary research findings and implications for infection control policy, and outlines future research directions. Environmental contamination has been reported in hospital settings occupied by infected patients, and is higher in the first week of illness. Transmission via environmental surfaces or fomites is likely, but decontamination protocols are effective in minimising this risk. The extent of airborne transmission is also unclear. While several studies have detected SARS-CoV-2 ribonucleic acid in air samples, none has isolated viable virus in culture. Transmission likely lies on a spectrum between droplet and airborne transmission, depending on the patient, disease and environmental factors. Singapore's current personal protective equipment and isolation protocols are sufficient to manage this risk.

Infectious SARS-CoV-2 in Exhaled Aerosols and Efficacy of Masks During Early Mild Infection

BackgroundSARS-CoV-2 epidemiology implicates airborne transmission; aerosol infectiousness and impacts of masks and variants on aerosol shedding are not well understood. MethodsWe recruited 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 two visits two days apart. We quantified and sequenced viral RNA, cultured virus, and assayed sera for anti-spike and anti-receptor binding domain antibodies. ResultsWe enrolled 49 seronegative cases (mean days post onset 3.8 {+/-}2.1), May 2020 through April 2021. We detected SARS-CoV-2 RNA in 45% of fine ([≤]5 {micro}m), 31% of coarse (>5 {micro}m) aerosols, and 65% of fomite samples overall and in all samples from four 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. ConclusionSARS-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. Key PointsO_LICases exhale infectious viral aerosols C_LIO_LISARS-CoV-2 evolution favors more efficient aerosol generation. C_LIO_LILoose-fitting masks moderately reduce viral RNA aerosol. C_LIO_LIVentilation, filtration, UV air sanitation, and tight-fitting masks are needed to protect vulnerable people in public-facing jobs and indoor spaces. C_LI

Viral Load of SARS-CoV-2 in Respiratory Aerosols Emitted by COVID-19 Patients while Breathing, Talking, and Singing

BackgroundMultiple SARS-CoV-2 superspreading events suggest that aerosols play an important role in driving the COVID-19 pandemic. However, the detailed roles of coarse (>5m) and fine ([≤]5m) respiratory aerosols produced when breathing, talking, and singing are not well-understood. MethodsUsing a G-II exhaled breath collector, we measured viral RNA in coarse and fine respiratory aerosols emitted by COVID-19 patients during 30 minutes of breathing, 15 minutes of talking, and 15 minutes of singing. ResultsAmong the 22 study participants, 13 (59%) emitted detectable levels of SARS-CoV-2 RNA in respiratory aerosols, including 3 asymptomatic patients and 1 presymptomatic patient. Viral loads ranged from 63-5,821 N gene copies per expiratory activity per patient. Patients earlier in illness were more likely to emit detectable RNA, and loads differed significantly between breathing, talking, and singing. The largest proportion of SARS-CoV-2 RNA copies was emitted by singing (53%), followed by talking (41%) and breathing (6%). Overall, fine aerosols constituted 85% of the viral load detected in our study. Virus cultures were negative. ConclusionsFine aerosols produced by talking and singing contain more SARS-CoV-2 copies than coarse aerosols and may play a significant role in the transmission of SARS-CoV-2. Exposure to fine aerosols should be mitigated, especially in indoor environments where airborne transmission of SARS-CoV-2 is likely to occur. Isolating viable SARS-CoV-2 from respiratory aerosol samples remains challenging, and whether this can be more easily accomplished for emerging SARS-CoV-2 variants is an important enquiry for future studies. Key PointsWe sampled respiratory aerosols emitted by COVID-19 patients and discovered that fine aerosols ([≤]5m) generated during talking and singing contain more SARS-CoV-2 copies than coarse aerosols (>5m) and may play a significant role in the transmission of SARS-CoV-2.

Detection of Air and Surface Contamination by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Hospital Rooms of Infected Patients

Understanding the particle size distribution in the air and patterns of environmental contamination of SARS-CoV-2 is essential for infection prevention policies. We aimed to detect SARS-CoV-2 surface and air contamination and study associated patient-level factors. 245 surface samples were collected from 30 airborne infection isolation rooms of COVID-19 patients, and air sampling was conducted in 3 rooms. Air sampling detected SARS-CoV-2 PCR-positive particles of sizes >4 {micro}m and 1-4 {micro}m in two rooms, which warrants further study of the airborne transmission potential of SARS-CoV-2. 56.7% of rooms had at least one environmental surface contaminated. High touch surface contamination was shown in ten (66.7%) out of 15 patients in the first week of illness, and three (20%) beyond the first week of illness (p = 0.010).