Bacteria in sputum of stable severe asthma and 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.The lower airways have until recently been considered to be a sterile environment, and in airway diseases such as bronchiectasis and COPD, the isolation of bacteria such as Haemophilus influenzae and Pseudomonas species in sputum samples by culture is not an uncommon event [1,2]. While these pathogens are often associated with exacerbations, they are also often present during stable phase of the airways disease indicating chronic colonisation. The isolation of bacterial pathogens in chronic asthma by culture remains understudied. In one report, 27% of asthmatic patients presenting with an exacerbation of asthma had bacteria in sputum with Streptococcus pneumonia, Streptococcus pyogenes, Staphylococcus aureus, Moraxella catarrhalis and Haemophilus influenzae [3]. This spectrum of bacterial species was also