The prevalence and significance of Staphylococcus aureus in patients with non-cystic fibrosis bronchiectasis

Rationale: Staphylococcus aureus is commonly cultured from the sputum of patients with bronchiectasis; however, little is known about the prevalence of the organism in these patients, the characteristics of patients who have grown the organism, or its implications. Objectives: Determine the relationship between S. aureus and pulmonary function, frequency of exacerbations, and frequency of hospitalization in patients with bronchiectasis Methods:TheBronchiectasisResearchRegistry is a database of adults with non-cystic fibrosis bronchiectasis identified from 13 sites within the United States. Baseline and follow-up demographic, spirometric, microbiologic, and therapeutic data were entered into a central webbased database. Patientswere grouped into three cohorts based on their previous respiratory cultures at the time of entry into theRegistry: 1) no prior S. aureus or glucose-nonfermenting gram-negative bacilli (NFGNB) (Pseudomonas, Stenotrophomonas, or Burkholderia spp.); 2) prior S. aureus at least once; or 3) no prior S. aureus but prior NF-GNB at least once. The association between S. aureus isolation and pulmonary function and frequency of exacerbations and hospital admissions was assessed, both at baseline and after 1 year of follow-up. Results: S. aureus was cultured from 94 of 830 patients (11.3%) included in the analysis. Patients who had grown S. aureus before entry into the Registry had a frequency of prior exacerbations and baseline pulmonary function that was between that of patients who had grown NF-GNB and those who had grown neither NF-GNB or S. aureus. Similarly, at the first follow-up visit after study entry, patients who had grown S. aureus had a frequency of exacerbations and hospitalizations that was between those of patients who had grown NF-GNB and those who had grown neither NF-GNB nor S. aureus. However, in multivariate analysis, S. aureus was not associated with pulmonary function, frequency of exacerbation, or hospital admissions. There were no significant differences in patient characteristics or outcomes between patients who had methicillin-sensitive and methicillin-resistant S. aureus. Conclusions: Staphylococcus aureus does not appear to be an independent risk factor for severe disease in patients with bronchiectasis enrolled in the Bronchiectasis Research Registry.