Dominant Pathogen in Bronchiectasis in Western Cohorts
Haemophilus influenzae is the most frequently isolated pathogen in bronchiectasis in Western populations, accounting for 20-40% of cases, followed by Pseudomonas aeruginosa at 10-30%. 1
Primary Pathogens in Order of Frequency
The bacterial colonization pattern in Western bronchiectasis cohorts follows a consistent hierarchy:
- Haemophilus influenzae: Most common pathogen (20-40% prevalence) 1
- Pseudomonas aeruginosa: Second most common (10-30% prevalence, with 15% chronic infection rate in European cohorts) 1, 2
- Moraxella catarrhalis: Less frequent than the above two 1
- Staphylococcus aureus: Less frequent 1
- Enterobacteriaceae: Less frequent 1
Clinical Significance of Pathogen Type
While H. influenzae is numerically dominant, P. aeruginosa carries disproportionate clinical importance despite lower prevalence due to its association with worse outcomes 1:
- Three-fold increase in mortality risk 1
- Seven-fold increase in hospitalization risk 1
- One additional exacerbation per patient per year on average 1
- Independently associated with worse quality of life (7.46 points worse on quality of life measures) 2
Colonization with any organism other than P. aeruginosa is associated with poorer outcomes compared to patients not colonized with pathogens 1, though the prognostic impact is less severe than with P. aeruginosa 1.
Important Clinical Caveats
The mortality impact of P. aeruginosa is particularly pronounced in patients with frequent exacerbations (≥2 per year), where it independently increases mortality risk (HR 2.03) 2. In patients without frequent exacerbations, P. aeruginosa does not independently predict mortality when adjusted for disease severity 2.
Persistent isolation of these organisms in sputum or bronchoalveolar lavage correlates with increased exacerbation frequency, worse quality of life, and increased mortality 1.