‘Coughs and sneezes spread diseases’. The replication and modelling of infectious respiratory aerosol.

Abstract

The air we breathe can harbour pathogens, including viruses and bacteria, that contribute to respiratory diseases at both endemic and pandemic levels. While previous research has addressed airborne microbial losses, the underlying mechanisms remain inadequately understood. This thesis aims to enhance disease transmission modelling and mitigate the impact of infectious respiratory diseases by exploring the physicochemical mechanisms behind microbial survival in the aerosol phase. By combining measurements of microbial aerostability with aerosol evaporation kinetics, we replicate and model infectious respiratory droplets using Escherichia coli and Mouse Hepatitis Virus. We identify appropriate respiratory fluid surrogates for microbial aerostability assessments by comparing them to clinically relevant saliva samples.Using the Controlled Electrodynamic Levitation and Extraction of Bioaerosols onto a Substrate (CELEBS) alongside single particle measurement systems such as the comparative kinetic electrodynamic balance (CKEDB). Our findings reveal that phase separation in evaporating droplets, influenced by mucin, can transiently protect viral particles from the adverse effects of particle phase change. Conversely, bacterial losses are predominantly affected by their localisation at the particle-air interface, where they are more susceptible to airborne disinfectants. However, both bacteria and viruses are susceptible to changes in pH of the evaporating aerosol. Additionally, we demonstrate that stress response mechanisms enhance the aerostability of Staphylococcus aureus, revealing significant differences in survival across species and strains. Ultimately, this research establishes a standardised protocol for microbial aerostability measurements, paving the way for future investigations into respiratory pathogens using CELEBS. This work can help to inform public health policy on the risks of aerosol disease transmission, and the use of mitigations to restrict their spread.

Date of Award	18 Mar 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Darryl J Hill (Supervisor) & Jonathan P Reid (Supervisor)