Infectious airborne transport in individuals with cystic fibrosis and mitigation strategies to reduce aerosol dispersal

Abstract

Background and Aims Cystic fibrosis (CF) is characterised by repeated bacterial respiratory infections and progressive lung disease. While Pseudomonas aeruginosa is the most prevalent organism recovered from the respiratory secretions of people with CF, other species including Staphylococcus aureus, Stenotrophomonas maltophilia, Achromobacter species, Burkholderia cepacia complex species, and Mycobacterium abscessus may also be detected. The majority of these pathogens are found in the natural environment and the identification of genetically diverse bacterial strains infecting people with CF would suggest that this is the most common acquisition source. However, epidemiological studies have demonstrated that some people with CF may harbour genetically indistinguishable (shared) strains of organisms. Common environmental reservoirs have not been identified for many shared strains, suggesting that person-to-person transmission may be a method of acquisition, although the exact mechanisms involved are unclear. The airborne route, involving inhalation of microbe-containing droplet nuclei, has been speculated as a possible transmission pathway. Previous studies have demonstrated that people with CF can generate droplet nuclei containing P. aeruginosa, which can survive for up to 45-minutes and can travel up to 4-metres from their source and therefore potentially capable of airborne transmission. The survival of other common CF pathogens over distance and time is not known. Recent updates to CF infection control guidelines in some countries recommend the use of a surgical face mask for people with CF to minimise risk of transmission and acquisition of such pathogens. The effectiveness of face masks in a CF population has not been studied extensively. To address the knowledge gaps highlighted above, this thesis had two key aims: i) To determine if CF pathogens other than P. aeruginosa can be aerosolised during coughing, and to investigate their survival in the air over distance and time and; ii) To examine the effectiveness of face masks and cough etiquette in reducing the outward dispersal of cough generated aerosols containing P. aeruginosa in people with CF. iii Methods i) Cough aerosolisation of cystic fibrosis respiratory pathogens (other than P. aeruginosa) Thirty-three participants with CF were enrolled, according to a recent history of infection with: 1) Gram-negative bacteria (GNB) other than P. aeruginosa; 2) S. aureus and; 3) M. abscessus complex. Using two validated systems for aerosol sampling, the viability and survival of cough aerosols were measured over distance and time. ii) Effectiveness of face masks and cough etiquette to reduce aerosol concentration of Pseudomonas aeruginosa Twenty-five participants with CF and chronic P. aeruginosa infection were enrolled. Six respiratory activities of talking and coughing, with and without face masks were undertaken within an aerosol sampling device. Aerosols were collected at 2-metres and quantitative analysis performed on bacterial colony forming units (CFU) f...