Exhaled aerosol increases with COVID-19 infection, and risk factors of disease symptom severity

Edwards, David A.; Ausiello, Dennis A.; Langer, Robert; Salzman, Jonathan; Devlin, Tom; Beddingfield, Brandon J; Fears, Alyssa C.; Doyle-Meyers, Lara A.; Redmann, Rachel K.; Killeen, Stephanie Z.; Maness, Nicholas J.; Roy, Chad J.

doi:10.1101/2020.09.30.20199828

Cited by 15 publications

(19 citation statements)

References 17 publications

(24 reference statements)

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“…Emerging evidence supports the risk of COVID-19 infection to be lower among critical care staff (who generally manage patients on both CPAP and HFNO) than other healthcare staff (OR 0.29; 95%CI 0.13-0.57 from our hospital 20 , similar results from other cohorts 19,21–24 ). There are many plausible explanations (fewer patients per clinician, patients presenting later in disease course), but one of the most likely is the use of more highly protective FFP3 masks by critical care staff.…”

Section: Discussionsupporting

confidence: 81%

“…This is the first study to report on aerosol emission from patients with active COVID-19, with previous work on primates only. 19 While the data available for analysis suggests that peak aerosol concentrations from coughs are higher than recorded from healthy volunteers without COVID-19 who were recruited in a laminar flow theatre, the background aerosol concentration on the ward was too high to make reliable inference about breathing and speaking. Some patients had lower emissions, which were not detectable above the non-zero background.…”

Section: Discussionmentioning

confidence: 99%

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Aerosol emission from the respiratory tract: an analysis of relative risks from oxygen delivery systems

Hamilton

Gregson

Arnold

et al. 2021

Preprint

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BackgroundRisk of aerosolisation of SARS-CoV-2 directly informs organisation of acute healthcare and PPE guidance. Continuous positive airways pressure (CPAP) and high-flow nasal oxygen (HFNO) are widely used modes of oxygen delivery and respiratory support for patients with severe COVID-19, with both considered as high risk aerosol generating procedures. However, there are limited high quality experimental data characterising aerosolisation during oxygen delivery and respiratory support.MethodsHealthy volunteers were recruited to breathe, speak, and cough in ultra-clean, laminar flow theatres followed by using oxygen and respiratory support systems. Aerosol emission was measured using two discrete methodologies, simultaneously. Hospitalised patients with COVID-19 were also recruited and had aerosol emissions measured during breathing, speaking, and coughing.FindingsIn healthy volunteers (n = 25 subjects; 531 measures), CPAP (with exhalation port filter) produced less aerosols than breathing, speaking and coughing (even with large >50L/m facemask leaks). HFNO did emit aerosols, but the majority of these particles were generated from the HFNO machine, not the patient. HFNO-generated particles were small (<1μm), passing from the machine through the patient and to the detector without coalescence with respiratory aerosol, thereby unlikely to carry viral particles. Coughing was associated with the highest aerosol emissions with a peak concentration at least 10 times greater the mean concentration generated from speaking or breathing. Hospitalised patients with COVID-19 (n = 8 subjects; 56 measures) had similar size distributions to healthy volunteers.InterpretationIn healthy volunteers, CPAP is associated with less aerosol emission than breathing, speaking or coughing. Aerosol emission from the respiratory tract does not appear to be increased by HFNO. Although direct comparisons are complex, cough appears to generate significant aerosols in a size range compatible with airborne transmission of SARS-CoV-2. As a consequence, the risk of SARS-CoV-2 aerosolisation is likely to be high in all areas where patients with Covid-19 are coughing. Guidance on personal protective equipment policy should reflect these updated risks.FundingNIHR-UKRI Rapid COVID call (COV003), Wellcome Trust GW4-CAT Doctoral Training Scheme (FH), MRC CARP Fellowship(JD, MR/T005114/1). Natural Environment Research Council grant (BB, NE/P018459/1)Research in contextEvidence before this studyPubMed was searched from inception until 10/1/21 using the terms ‘aerosol’, and variations of ‘non-invasive positive pressure ventilation’ and ‘high-flow nasal oxygen therapy’. Studies were included if they measured aerosol generated from volunteers or patients receiving non-invasive positive pressure ventilation (NIV) or high flow nasal oxygen therapy (HFNO), or provided experimental evidence on a simulated human setting. One study was identified (Gaeckle et al, 2020) which measured aerosol emission with one methodology (APS) but was limited by high background concentration of aerosol and a low number of participants (n = 10).Added value of this studyThis study used multiple methodologies to measure aerosol emission from the respiratory tract before and during CPAP and high-flow nasal oxygen, in an ultra-clean, laminar flow theatre with near-zero background aerosol and recruited patients with COVID-19 to ensure similar aerosol distributions. We conclude that there is negligible aerosol generation with CPAP, that aerosol emission from HFNO is from the machine and not the patient, coughing emits aerosols consistent with airborne transmission of SARS CoV2 and that healthy volunteers are a reasonable proxy for COVID-19 patients.Implications of all the available evidenceCPAP and HFNO should not be considered high risk aerosol generating procedures, based on our study and that of Gaeckle et al. Recorded aerosol emission from HFNO stems from the machine. Cough remains a significant aerosol risk. PPE guidance should be updated to ensure medical staff are protected with appropriate PPE in situations when patients with suspected or proven COVID-19 are likely to cough.

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Section: Discussionsupporting

confidence: 81%

Section: Discussionmentioning

confidence: 99%

Aerosol emission from the respiratory tract: an analysis of relative risks from oxygen delivery systems

Hamilton

Gregson

Arnold

et al. 2021

Preprint

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“…Breathing may, for instance, sometimes shed more of the virus than coughing because it is continuous, and coughs are less frequent [ 54 ]. Some individuals also emit substantially higher amounts of particles than average [ 55 , 56 ].…”

Section: Discussionmentioning

confidence: 99%

Indoor Model Simulation for COVID-19 Transport and Exposure

Hussein

Löndahl

Thuresson

et al. 2021

IJERPH

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Transmission of respiratory viruses is a complex process involving emission, deposition in the airways, and infection. Inhalation is often the most relevant transmission mode in indoor environments. For severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the risk of inhalation transmission is not yet fully understood. Here, we used an indoor aerosol model combined with a regional inhaled deposited dose model to examine the indoor transport of aerosols from an infected person with novel coronavirus disease (COVID-19) to a susceptible person and assess the potential inhaled dose rate of particles. Two scenarios with different ventilation rates were compared, as well as adult female versus male recipients. Assuming a source strength of 10 viruses/s, in a tightly closed room with poor ventilation (0.5 h−1), the respiratory tract deposited dose rate was 140–350 and 100–260 inhaled viruses/hour for males and females; respectively. With ventilation at 3 h−1 the dose rate was only 30–90 viruses/hour. Correcting for the half-life of SARS-CoV-2 in air, these numbers are reduced by a factor of 1.2–2.2 for poorly ventilated rooms and 1.1–1.4 for well-ventilated rooms. Combined with future determinations of virus emission rates, the size distribution of aerosols containing the virus, and the infectious dose, these results could play an important role in understanding the full picture of potential inhalation transmission in indoor environments.

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“…In contrast to the primary function of masks to prevent virus from entering the respiratory tract of another person [45, 46], this additional benefit applies after a virus-containing particle lands on the surface of the respiratory tract: reduced dehydration limits impairment of the innate immune system [14] while improving mucociliary clearance [16, 17], with both these factors reducing infection probability. If an infection does occur, humidification may limit its further spread through the lungs by lowering the generation of virus-containing breath droplets that could lead to self-inoculation elsewhere in the lungs [18, 19]. At the same time, effective mucociliary clearance and an unimpaired innate immune system of the well-humidified respiratory tract also may limit viral spreading, allowing more time for mobilization of the adaptive immune system.…”

Section: Discussionmentioning

confidence: 99%

“…Despite their small size, such droplets are still one to three orders of magnitude larger in volume than the SARS-CoV-2 virus and therefore can easily encapsulate one or more virions. Moreover, recent work indicates a strong increase in droplet count upon SARS-CoV-2 infection of the lungs of non-human primates [19], as well as high levels of viral shedding in the exhaled breath of hospitalized patients [20].…”

Section: Introductionmentioning

confidence: 99%

Hydrating the Respiratory Tract: An Alternative Explanation Why Masks Lower Severity of COVID-19 Disease

Courtney

Bax

2020

Preprint

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Seasonality of respiratory diseases has been linked, among other factors, to low outdoor absolute humidity and low relative humidity in indoor environments, which increase evaporation of water in the mucosal layer lining the respiratory tract. We demonstrate that normal breathing results in an absorption-desorption cycle inside facemasks, where super-saturated air is absorbed by the mask fibers during expiration, followed by evaporation during inspiration of dry environmental air. For double-layered cotton masks, which have considerable heat capacity, the temperature of inspired air rises above room temperature, and the effective increase in relative humidity can exceed 100%. We propose that the recently reported, disease-attenuating effect of generic facemasks is dominated by the strong humidity increase of inspired air.SIGNIFICANCE STATEMENTFacemasks are the most widely used tool for mitigating the spread of the COVID-19 pandemic. Decreased disease severity by the wearer has also been linked to the use of cloth facemasks. This well-documented finding is surprising considering that such masks are poor at filtering the smallest aerosol particles, which can reach the lower respiratory tract and have been associated with severe disease. We show that facemasks strongly increase the effective humidity of inhaled air, thereby promoting hydration of the respiratory epithelium which is known to be beneficial to the immune system. Increased humidity of inspired air could be an alternate explanation for the now well-established link between mask wearing and lower disease severity.

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Exhaled aerosol increases with COVID-19 infection, and risk factors of disease symptom severity

Cited by 15 publications

References 17 publications

Aerosol emission from the respiratory tract: an analysis of relative risks from oxygen delivery systems

Aerosol emission from the respiratory tract: an analysis of relative risks from oxygen delivery systems

Indoor Model Simulation for COVID-19 Transport and Exposure

Hydrating the Respiratory Tract: An Alternative Explanation Why Masks Lower Severity of COVID-19 Disease

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