Cough-generated Aerosols of Pseudomonas aeruginosa and other Bacteria from Cystic Fibrosis Patients

Claire E Wainwright ^1*, Megan W France ², Peter O'Rourke ³, Snehal Anuj ⁴, Timothy J Kidd ⁵, Michael D Nissen ⁵, Theo P Sloots ⁶, Chris Coulter ², Zoran Ristovski ⁷, Megan Hargreaves ⁷, Barbara R Rose ⁸, Colin Harbour ⁸, Scott C Bell ² and Kevin P Fennelly ⁹

¹ Royal Children's Hospital, Brisbane, Australia
² The Prince Charles Hospital, Australia
³ Queensland Institute of Medical Research, Australia
⁴ University of Queensland, Australia
⁵ Pathology Queensland, Australia
⁶ Sir Albert Sakzewski Virus Research Centre, Australia
⁷ Queensland Institute of Technology, Australia
⁸ University of Sydney, Australia
⁹ UMDNJ - New Jersey Medical School, United States

^* To whom correspondence should be addressed. E-mail: claire_wainwright{at}health.qld.gov.au.

Accepted 15 June 2009

Abstract

Background: Pseudomonas aeruginosa is the most common bacterial pathogen in cystic fibrosis (CF) patients. Current infection control guidelines aim to prevent transmission via contact and respiratory droplet routes and do not consider the possibility of airborne transmission. We hypothesized that with coughing, CF subjects produce viable, respirable bacterial aerosols.

Methods: Cross-sectional study of 15 children and 13 adults with CF, 26 chronically infected with P. aeruginosa. A cough aerosol sampling system enabled fractioning of respiratory particles of different size, and culture of viable Gram negative non-fermentative bacteria. We collected cough aerosols during 5 minutes voluntary coughing and during a sputum induction procedure when tolerated. Standardized quantitative culture and genotyping techniques were used.

Results: P. aeruginosa was isolated in cough aerosols of 25 (89%) subjects of whom 22 produced sputum samples. P. aeruginosa from sputum and paired cough aerosols were indistinguishable by molecular typing. In 4 cases the same genotype was isolated from ambient room air. Approximately 70% of viable aerosols collected during voluntary coughing were of particles 3.3 microns aerodynamic diameter. P. aeruginosa, Burkholderia cenocepacia Stenotrophomonas maltophilia and Achromobacter xylosoxidans were cultivated from respiratory particles in this size range. Positive room air samples were associated with high total counts in cough aerosols (P=0.003). The magnitude of cough aerosols were associated with higher FEV1 (r=0.45, P=0.02) and higher quantitative sputum culture results (r=0.58, P=0.008).

Conclusion: During coughing, CF patients produce viable aerosols of P. aeruginosa and other Gram negative bacteria of respirable size range, suggesting the potential for airborne transmission.