Staphylococcus aureus in Patients Diagnosed With Bronchiectasis Without Cystic Fibrosis

The presence of S aureus was not found to confer higher risk of more severe bronchiectasis. Photo Credit: Frank DeLeo, NIAID, CDC

Patients diagnosed with bronchiectasis and in whom sputum cultures grow Staphylococcus aureus may not experience a difference in exacerbation frequency, forced expiratory volume in 1 second (FEV1) decline, or hospital admission rates compared with patients with bronchiectasis in whom sputum cultures do not grow S aureus after adjusting for patient characteristics, according to research published in the Annals of the American Thoracic Society.

Using the United States Bronchiectasis Research Registry, investigators identified 830 patients diagnosed with bronchiectasis from 13 sites. Individuals were placed into 1 of 3 groups based upon the organism that grew during previous respiratory cultures:

No previous infection of S aureus or glucose nonfermenting Gram-negative bacilli (NF-GNB)
History of at least 1infection with S aureus
No previous history of S aureus infection, but positive history of at least 1 NF-GNB infection (Pseudomonas, Stenotrophomonas, or Burkholderia species)

The purpose of the study was to assess, at baseline and after 1 year, the relationship between a S aureus-positive bronchiectasis infection and pulmonary function, frequency of exacerbations, and hospital admissions.

Of the 830 patients included in the study, sputum cultures from 11.3% (n=94) grew S aureus (22 [33%] identified as methicillin-resistant S aureus [MRSA]), while sputum cultures from 34% also grew Pseudomonas, Stenotrophomonas, or Burkholderia. Patients in whom sputum cultures grew S aureus were found to be more often men, to have experienced a pulmonary exacerbation within the last 2 years, and to have a lower average pre-bronchodilator FEV1 when compared with patients in whom sputum cultures did not grow any of the above-listed pathogens.

The investigators found that patients in whom sputum cultures grew S aureus at baseline had average rates of exacerbation and hospitalizations between those associated with no pathogens and those associated with Gram-negative pathogens. There were no significant differences in outcomes identified between patients with sputum that grew none of the targeted pathogens and those with sputum that grew S aureus for number of exacerbations or hospitalizations after adjustments were made for patient characteristics, length of time between baseline visits, and follow-up visits (incidence rate ratio [RR] 1.20 [95% CI, 0.82-1.76] and RR 0.98 [95% CI, 0.49-1.98], respectively). The mean difference between these two groups in FEV1 was found to be 0.06 L (95% CI, -0.17 to 0.06).

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The researchers concluded that individuals with bronchiectasis do not appear to be at higher risk for a more severe form of the disease based upon the presence of S aureus, as it was not identified in this study as an independent risk factor. However, the investigators noted that the research suggested “colonization or infection with S aureus might be a marker for more severe disease, but does not support a causal link between S aureus and worsened bronchiectasis patient outcomes.” It is also interesting to note that outcomes and patient characteristics did not appear to be significantly different in individuals with sputum that grew methicillin-sensitive S aureus compared with MRSA. Therefore, clinicians should note that the presence of S aureus may serve as a marker for more severe disease as opposed to an actual causal factor of more severe disease in individuals with bronchiectasis.