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JAMA Netw Open ; 3(7): e2013807, 2020 07 01.
Article in English | MEDLINE | ID: covidwho-680218


Importance: Individuals with asymptomatic or mild coronavirus disease 2019 (COVID-19) have been reported to frequently transmit the disease even without direct contact. The severe acute respiratory syndrome coronavirus 2 has been found at very high concentrations in swab and sputum samples from such individuals. Objective: To estimate the virus levels released from individuals with asymptomatic to moderate COVID-19 into different aerosol sizes by normal breathing and coughing, and to determine what exposure could result from this in a room shared with such individuals. Design, Setting, and Participants: This mathematical modeling study combined the size-distribution of exhaled breath microdroplets for coughing and normal breathing with viral swab and sputum concentrations as approximation for lung lining liquid to obtain an estimate of emitted virus levels. Viral data were obtained from studies published as of May 20, 2020. The resulting emission data fed a single-compartment model of airborne concentrations in a room of 50 m3, the size of a small office or medical examination room. Main Outcomes and Measures: Modeling was used to estimate the viral load emitted by individuals breathing normally or coughing, and the concentrations expected in the simulated room at different ventilation rates. Results: The mean estimated viral load in microdroplets emitted by simulated individuals while breathing regularly was 0.0000049 copies/cm3, with a range of 0.0000000049 to 0.637 copies/cm3. The corresponding estimates for simulated coughing individuals were a mean of 0.277 copies/cm3 per cough, with a range of 0.000277 to 36 030 copies/cm3 per cough. The estimated concentrations in a room with an individual who was coughing frequently were very high, with a maximum of 7.44 million copies/m3 from an individual who was a high emitter. However, regular breathing from an individual who was a high emitter was modeled to result in lower room concentrations of up to 1248 copies/m3. Conclusions and Relevance: In this modeling study, breathing and coughing were estimated to release large numbers of viruses, ranging from thousands to millions of virus copies per cubic meter in a room with an individual with COVID-19 with a high viral load, depending on ventilation and microdroplet formation process. The estimated infectious risk posed by a person with typical viral load who breathes normally was low. The results suggest that only few people with very high viral load pose an infection risk in poorly ventilated closed environments. These findings suggest that strict respiratory protection may be needed when there is a chance to be in the same small room with an individual, whether symptomatic or not, especially for a prolonged period.

Asymptomatic Diseases , Coronavirus Infections/transmission , Coronavirus Infections/virology , Cough/virology , Exhalation/physiology , Models, Statistical , Pneumonia, Viral/transmission , Pneumonia, Viral/virology , Viral Load , Betacoronavirus , Coronavirus Infections/epidemiology , Environment , Humans , Pandemics , Pneumonia, Viral/epidemiology , Ventilation
Nat Med ; 26(5): 676-680, 2020 05.
Article in English | MEDLINE | ID: covidwho-203367


We identified seasonal human coronaviruses, influenza viruses and rhinoviruses in exhaled breath and coughs of children and adults with acute respiratory illness. Surgical face masks significantly reduced detection of influenza virus RNA in respiratory droplets and coronavirus RNA in aerosols, with a trend toward reduced detection of coronavirus RNA in respiratory droplets. Our results indicate that surgical face masks could prevent transmission of human coronaviruses and influenza viruses from symptomatic individuals.

Coronavirus Infections/transmission , Masks/virology , Pneumonia, Viral/transmission , Respiratory Tract Infections/transmission , Aerosols/isolation & purification , Coronavirus Infections/prevention & control , Coronavirus Infections/virology , Exhalation/physiology , Humans , Orthomyxoviridae/isolation & purification , Orthomyxoviridae/pathogenicity , Pandemics/prevention & control , Pneumonia, Viral/prevention & control , Pneumonia, Viral/virology , RNA, Viral/isolation & purification , Respiratory Tract Infections/pathology , Respiratory Tract Infections/virology , Virus Shedding
Anaesthesia ; 75(8): 1086-1095, 2020 08.
Article in English | MEDLINE | ID: covidwho-88703


Healthcare workers are at risk of infection during the severe acute respiratory syndrome coronavirus-2 pandemic. International guidance suggests direct droplet transmission is likely and airborne transmission occurs only with aerosol-generating procedures. Recommendations determining infection control measures to ensure healthcare worker safety follow these presumptions. Three mechanisms have been described for the production of smaller sized respiratory particles ('aerosols') that, if inhaled, can deposit in the distal airways. These include: laryngeal activity such as talking and coughing; high velocity gas flow; and cyclical opening and closure of terminal airways. Sneezing and coughing are effective aerosol generators, but all forms of expiration produce particles across a range of sizes. The 5-µm diameter threshold used to differentiate droplet from airborne is an over-simplification of multiple complex, poorly understood biological and physical variables. The evidence defining aerosol-generating procedures comes largely from low-quality case and cohort studies where the exact mode of transmission is unknown as aerosol production was never quantified. We propose that transmission is associated with time in proximity to severe acute respiratory syndrome coronavirus-1 patients with respiratory symptoms, rather than the procedures per se. There is no proven relation between any aerosol-generating procedure with airborne viral content with the exception of bronchoscopy and suctioning. The mechanism for severe acute respiratory syndrome coronavirus-2 transmission is unknown but the evidence suggestive of airborne spread is growing. We speculate that infected patients who cough, have high work of breathing, increased closing capacity and altered respiratory tract lining fluid will be significant producers of pathogenic aerosols. We suggest several aerosol-generating procedures may in fact result in less pathogen aerosolisation than a dyspnoeic and coughing patient. Healthcare workers should appraise the current evidence regarding transmission and apply this to the local infection prevalence. Measures to mitigate airborne transmission should be employed at times of risk. However, the mechanisms and risk factors for transmission are largely unconfirmed. Whilst awaiting robust evidence, a precautionary approach should be considered to assure healthcare worker safety.

Betacoronavirus , Coronavirus Infections/transmission , Health Personnel , Infectious Disease Transmission, Patient-to-Professional , Pneumonia, Viral/transmission , Aerosols , Air Microbiology , Cardiopulmonary Resuscitation/adverse effects , Coronavirus Infections/physiopathology , Coronavirus Infections/prevention & control , Exhalation/physiology , Humans , Infection Control/methods , Infectious Disease Transmission, Patient-to-Professional/prevention & control , Masks , Nebulizers and Vaporizers , Pandemics/prevention & control , Particle Size , Pneumonia, Viral/physiopathology , Pneumonia, Viral/prevention & control , Respiratory Physiological Phenomena