Cystic fibrosis (CF) is a progressive hereditary disease characterised by persistent pulmonary infections and lung function decline. Inhalation of airborne droplets containing microorganisms has been speculated as a possible transmission pathway for some of these pulmonary infections. Transmission of infectious aerosols is already a well-recognised route of infection for a number of diseases including Tuberculosis and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which is currently causing a world pandemic. Understanding this route of transmission for pathogens associated with CF and how the indoor environment affects this process is essential for developing effective infection control guidelines to further minimise the risk of cross-infection between people with CF.
Droplet size distributions of artificially generated aerosols of P. aeruginosa and M. abscessus were measured in a sealed constant air flow environment, the bioaerosol characterisation apparatus (BACA). Comparison between the two bacteria found M. abscessus decayed at a slower rate . Despite this several strains of both bacteria were found to easily survive in air for up to 4m without significant decay.
A cross-sectional study measuring cough/exhaled breath aerosols from people with CF in a clinical setting provided clear evidence that P. aeruginosa can be aerosolised by people with CF and initial evidence that M. abscessus is in exhaled breath. Analysis of the bioaerosol size distributions found that droplets containing culturable bacteria were dominated by sizes within the respirable range.
The clinical data was used to calculate microbial emission rates from people with CF which were used within a mathematical model to determine the probable concentration of bacteria in a room, the exposure and ultimately the risk of infection to a susceptible individual. Analysis highlighted that high emitters were likely to drive the high risks and ventilation and managing the interaction of patients played an important role in reducing the likelihood of infection.
This thesis demonstrates that two pathogens associated with CF are likely to be aerosolised by people with CF and can survive in air and travel up to 4m in droplets within the respirable size range. Overall, the risk of infection for a person with CF is low but this can significantly increase in the case of high emitters or when considering risk to the whole patient population at a CF unit. These findings strengthen the evidence for airborne transmission as a route of infection and support the need for continued stringent infection control practices for people with CF.
