Elucidating Airborne SARS-CoV-2 Infectivity at Single Aerosol Resolution

PROJECT SUMMARY In this emergency R21 effort we propose to implement a set of novel studies designed to improve our fundamental understanding of SARS-CoV-2 aerobiology. Through a combination of theoretical, experimental, and epidemiological data, there is emerging consensus that respiratory aerosols play a primary role in the transmission of COVID-19. However, despite the importance of understanding the fundamental mechanisms involved in the airborne transmission route, a number of basic questions central to SARS-CoV-2 aerobiology remain unanswered. In particular, the distribution of SARS-CoV-2 particles within different aerosol size populations has not yet been studied in detail, nor is there data available to predict the viability and infectivity of individual airborne virus particles within different aerosol populations. Furthermore, it is not currently known whether the virus tends to be uniformly distributed within a given aerosol population or clustered within a small number of aerosol droplets, an essential question for understanding the quantum of infection for COVID-19 transmission. To address these challenges, we propose a novel analytical approach combining efficient sampling of exhaled breath, high resolution fractionation of aerosol ensembles, and coupled analysis of inactive and infective virus particles within the collected aerosol fractions through a combination of RT-PCR and viral plaque assays. Significantly, aerosol fractionation will be performed using an Aerodynamic Aerosol Classifier as a unique technology for isolating monodisperse aerosol populations. In addition, a new technique for discretizing the collected aerosol particles will be implemented using a thermo-responsive hydrogel for aerosol deposition, allowing the particles to be delivered to cell culture while remaining spatially isolated and elucidating virus distribution and clustering within a given size fraction. The combined data sets resulting from the proposed studies will provide a first view of the distribution and conformation of SARS-CoV-2 within respiratory aerosols, and the relationships between aerosol properties (size, virus content, virus distribution, and clustering) and downstream infectivity. We anticipate that the improved understanding of aerosolized virus infectivity emerging from these studies will illuminate fundamental aspects of COVID-19 airborne transmission and allow us to identify the quantum of infection associated with SARS-CoV-2, thus supporting accurate modeling of transmission dynamics and guiding improved recommendations for PPE, room ventilation, and sanitation protocols to enhance intervention and minimize transmission of the virus.