The relationship between airway bacterial load and airways inflammation in stable non-cystic fibrosis bronchiectasis

Objective: To investigate the relationship between airway bacterial load and markers of airways inflammation in stable patients with bronchiectasis. Methods: 302 patients with non-CF bronchiectasis confirmed by HRCT were enrolled. At 6 monthly review, spontaneous sputum samples were processed to determine bacterial load, expressed as log 10 colony forming units/ml (cfu/ml). Sputum sol was analysed for myeloperoxidase (MPO) and neutrophil elastase elastase activity. Interleukin-8 (IL-8), Interleukin 1-beta (IL-1β) and tumour necrosis factor alpha (TNF-α) were measured by ELISA. Results: 67 patients (22.1%) of patients grew no pathogens. Pathogenic micro-organisms were obtained in 77.9% of patients, most frequently Haemophilus influenzae (37.4% of isolates), Pseudomonas aeruginosa (20.4%), Staphylococcus aureus (13.2%), Streptococcus pneumoniae (11.9%) and Moraxella catarrhalis (10.6%). Airway inflammation increased progressively with increasing bacterial load. Statistically significant differences were observed, when compared to patients with no pathogens, at bacterial loads above 1×10 6 cfu/ml for MPO (p=0.01), neutrophil elastase activity (p=0.006) and IL-8 (p=0.02), and above 1×10 7 for TNF-α (p=0.04) and above 1×10 5 for IL-1β (p=0.003). Conclusion: There is a direct relationship between airway bacterial load and the degree of airway inflammation in stable bronchiectasis.