Quantitative Microbial Risk Assessment for Airborne Transmission of SARS-CoV-2 via Breathing, Speaking, Singing, Coughing, and Sneezing

Abstract

BACKGROUND: Evidence for indoor airborne transmission of SARS-CoV-2 is accumulating. OBJECTIVES: We assessed of the risk of illness due to airborne SARS-CoV-2 particles from breathing, speaking, singing, coughing, and sneezing in indoor environments. METHODS: A risk assessment model, AirCoV2, for exposure to SARS-CoV-2 particles in aerosol droplets was developed. Previously published data on droplets expelled by breathing, speaking, singing, coughing, and sneezing by an infected person were used as inputs. Scenarios encompassed virus concentration, exposure time, and ventilation. Newly collected data of virus RNA copies in mucus from patients are presented. RESULTS: The expelled volume of aerosols was highest for a sneeze, followed by a cough, singing, speaking, and breathing. After 20 min of exposure, at 10 7 RNA copies/mL in mucus, all mean illness risks were largely estimated to be below 0.001, except for the "high" sneeze scenario. At virus concentrations above 10 8 RNA copies/mL, and after 2 h of exposure, in the high and "low" sneeze scenarios, the high cough scenario and the singing scenario, risks exceeded 0.01 and may become very high, whereas the low coughing scenario, the high and low speaking scenarios and the breathing scenario remained below 0.1. After 2 h of exposure, singing became the second highest risk scenario. One air exchange per hour reduced risk of illness by about a factor of 2. Six air exchanges per hour reduced risks of illness by a factor of 8-13 for the sneeze and cough scenarios and by a factor of 4-9 for the other scenarios. DISCUSSION: The large variation in the volume of expelled aerosols is discussed. The model calculations indicated that SARS-CoV-2 transmission via aerosols outside of the 1:5-m social distancing norm can occur. Virus concentrations in aerosols and/or the amount of expelled aerosol droplets need to be high for substantial transmission via this route. AirCoV2 is made available as interactive computational tool.

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“…[ 15 ]: – number of infected persons, - – viral load in the sputum, – conversion factor is defined as the ratio between one infectious quantum and the infectious dose expressed in viral RNA copies (quanta/RNA). Schijven et al [ 32 ] developed a dose-response relationship that estimated an average of 1440 viral copies per infectious dose of SARS-CoV-2. Therefore, we estimated – ( – inhalation rate, i.e., the product of breathing ( and tidal volume ( ) –are both functions of the activity level of the infected subject.…”

“… – conversion factor is defined as the ratio between one infectious quantum and the infectious dose expressed in viral RNA copies (quanta/RNA). Schijven et al [ 32 ] developed a dose-response relationship that estimated an average of 1440 viral copies per infectious dose of SARS-CoV-2. Therefore, we estimated …”

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“…COVID-19 can be transmitted via different routes, including virus-laden particles aerosolized due to human activities such as breathing, speaking, singing, coughing, sneezing, etc. ( Bahl et al, 2021 ; CDC, 2021 ; Ma et al, 2021 ; Morawska and Cao, 2020 , Morawska and Milton, 2020 ; Schijven et al, 2021 ). Better recognized for producing larger droplets, coughing and sneezing also aerosolize tremendous amounts of small aerosol particles ( Lindsley et al, 2012 ; Han et al, 2013 ), primarily in the sub-micrometer size range.…”