Distribution of microbial pathogens into aerosol and the implications for airborne infection transmission

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Airborne transmission is important for a number of infections including TB, measles, Covid-19 and influenza. Transmission relies on microorganisms within the human respiratory system to be released in aerosols that are small enough to remain airborne for sufficient time and concentration to be inhaled by a susceptible person. Transmission models using either mass balance models or CFD simulations rely on assumptions about how microorganisms are distributed in aerosol; most models assume distribution is uniform by volume. However experimental data measuring viral emissions suggests that there may be proportionally more pathogens in the smaller aerosols. This may be an artefact of measurement methods, or it may result from the properties of the fluid, microorganism or mechanisms for aerosol generation; there are studies of sea aerosols and data from TB studies that suggests enrichment into smaller aerosols. This project aims to explore this phenomena and to evaluate the implications for modelling transmission risks. The project will involve (i) systematic review of published literature to understand the current evidence for partitioning of microorganisms into different aerosol sizes, measurement approaches for microbial aerosols and the fluid dynamics of respiratory aerosol generation (ii) experimental studies using controlled generation of microbial aerosols in a specialist test chamber facility and potentially studies of aerosol emissions from human sources, and (iii) applying different assumptions around microbial partitioning into CFD or risk models to explore how this would influence the predicted risk of infection.