Bacteria in sputum of stable severe asthma and increased airway wall thickness
1 Airways Disease Section, National Heart & Lung Institute, Imperial College, London, UK
2 State Key Laboratory of Respiratory Diseases, The First Affiliated Hospital, Guangzhou Medical University, Guangzhou, China
3 Respiratory Biomedical Research Unit, Royal Brompton & Harefield NHS Trust, London, UK
4 Department of Radiology, Royal Brompton & Harefield NHS Trust, London, UK
5 Department of Microbiology, Royal Brompton & Harefield NHS Trust, London, UK
6 Experimental Studies Unit, Imperial College, National Heart and Lung Institute, Dovehouse Street, London SW3 6LY, UK
Respiratory Research 2012, 13:35 doi:10.1186/1465-9921-13-35Published: 18 April 2012
Patients with chronic asthma have thicker intrapulmonary airways measured on high resolution computed tomography (HRCT). We determined whether the presence of lower airway bacteria was associated with increased airway wall thickness.
In 56 patients with stable severe asthma, sputum specimens obtained either spontaneously or after induction with hypertonic saline were cultured for bacteria and thoracic HRCT scans obtained. Wall thickness (WT) and area (WA) expressed as a ratio of airway diameter (D) and total area, respectively, were measured at five levels.
Positive bacterial cultures were obtained in 29 patients, with H. influenzae, P. aeruginosa and S. aureus being the commonest strains. Logistic regression analysis showed that this was associated with the duration of asthma and the exacerbations during the past year. In airways > 2 mm, there was no significant difference in WA (67.5 ± 5.4 vs 66.4 ± 5.4) and WT/D (21.6 ± 2.7 vs 21.3 ± 2.4) between the culture negative versus positive groups. Similarly, in airways (≤ 2 mm), there were no significant differences in these parameters. The ratio of √wall area to Pi was negatively correlated with FEV1% predicted (p < 0.05).
Bacterial colonization of the lower airways is common in patients with chronic severe asthma and is linked to the duration of asthma and having had exacerbations in the past year, but not with an increase in airway wall thickness.