Link between SARS-CoV-2 emissions and airborne concentrations: Closing the gap in understanding

Abstract

The airborne transmission of SARS-CoV-2 remains surprisingly controversial; indeed, health and regulatory authorities still require direct proof of this mode of transmission. To close this gap, we measured the viral load of SARS-CoV-2 of an infected subject in a hospital room (through an oral and nasopharyngeal swab), as well as the airborne SARS-CoV-2 concentration in the room resulting from the person breathing and speaking. Moreover, we simulated the same scenarios to estimate the concentration of RNA copies in the air through a novel theoretical approach and conducted a comparative analysis between experimental and theoretical results. Results showed that for an infected subject's viral load ranging between 2.4 × 10 6 and 5.5 × 10 6 RNA copies mL -1 , the corresponding airborne SARS-CoV-2 concentration was below the minimum detection threshold when the person was breathing, and 16.1 (expanded uncertainty of 32.8) RNA copies m -3 when speaking. The application of the predictive approach provided concentrations metrologically compatible with the available experimental data (i.e. for speaking activity). Thus, the study presented significant evidence to close the gap in understanding airborne transmission, given that the airborne SARS-CoV-2 concentration was shown to be directly related to the SARS-CoV-2 emitted. Moreover, the theoretical analysis was shown to be able to quantitatively link the airborne concentration to the emission.

SARS‐CoV‐2 indoor environment contamination with epidemiological and experimental investigations

“…Outside of the laboratory, signs of viable SARS‐CoV‐2 in the air have been detected, 10‐12 and the virus has also been cultured from exhaled air 13 . A direct link between SARS‐CoV‐2 viral load, emission, and airborne concentration was recently demonstrated by Buonanno et al 14 A few studies have detected SARS‐CoV‐2 RNA in the air at home‐environment 15,16 . In hospitals, PCR‐based studies have found SARS‐CoV‐2 RNA in room air, 17‐25 as well as from air conditioning filters located over 50 m from the patient room 26 .…”

Modeling Clothing as a Vector for Transporting Airborne Particles and Pathogens across Indoor Microenvironments

“…This volumetric state variable was chosen because of its potential to be used to estimate infection risk mechanistically (though such estimation of infection risk was left for future work). Previous modeling studies have performed such “bottom-up” estimations by (1) combining estimates of particle volume with empirical data on viral load to derive corresponding viral doses and then (2) combining these viral dose estimates with empirically derived dose–response relationships to estimate infection risks. ,− There are several uncertainties in estimating viral dose and corresponding infection risk based on particle volume, which are discussed in the Discussion section.…”

Human factors affecting ventilation in Australian classrooms during the COVID-19 pandemic: Toward insourcing occupants' proficiency in ventilation management

“…The COVID pandemic has thrust a spotlight on the relationship between indoor ventilation and disease transmission, where there is now exceptionally strong evidence that the pathogen responsible for COVID infection is transmitted primarily via respirated particles suspended in air (Morawska and Milton, 2020;Buonanno et al, 2022). Based on scientific evidence in this area, OzSAGE, an organization of scientists providing independent advice to the Australian government, advises that:…”

“…The relationship between poor IAQ and reduced productivity, concentration and decision making ability has long been identified in classrooms (Fisk, 2017) and offices (Wargocki and Wyon, 2013;Zhang et al, 2017). Yet the COVID pandemic has thrust the importance of room ventilation into the international spotlight, as the disease is proven to be more readily transmitted through particulates exhaled in human breath than through touching contaminated surfaces (Morawska and Milton, 2020;Buonanno et al, 2022;Gulland, 2022). Classrooms have remained of particular interest to air quality scientists pre-and during-COVID, given their high occupant densities and consideration given to children's developing respiratory systems (Gurdasani et al, 2021).…”