A new study on the clinical outcomes of cystic fibrosis revealed that patients infected only by Staphylococcus aureus infection in the absence of Pseudomonas aeruginosa led to milder disease. The study entitled “Clinical outcomes associated with Staphylococcus aureus and Pseudomonas aeruginosa airway infections in adult cystic fibrosis patients” was published this June at the BMC Pulmonary Medicine by researchers from McGill University, Montreal, Canada.
Cystic Fibrosis (CF) is a rare but well described genetic chronic respiratory disease, characterized by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) protein, and is associated with chronic polymicrobial infections of the lung among, which Pseudomonas aeruginosa (Pa) and Staphylococcus aureus (S. Aureus) are the most prevalent microorganisms. Pseudomonas aeruginosa is the predominant airway pathogen, affecting up to 60–75 % of adult CF patients and is strongly linked with inflammation, lung function decrease and increased mortality. On the other hand, Staphylococcus aureus (S. Aureus) is the most important cause of childhood pulmonary infection and is frequently isolated in children with CF.
Until now, the studies evaluating SA infections have mainly focused on CF children where the prevalence of SA infections is higher. As a result of this, the clinical significance of SA infections in adults has not been well established, contrary to children.
The research team performed a retrospective cross-sectional study to examine the association between airway infection (SA alone, PA, or neither) and lung function as well as pulmonary exacerbation rate in adults with cystic fibrosis. The lung function was measured using predicted FEV1 %, which is the volume exhaled during the first second of a forced expiratory maneuver started from the level of total lung capacity. FEV1 is the most frequently used index for assessing airway obstruction, bronchoconstriction or bronchodilatation. They also evaluated several secondary parameters, such as plasma C-reactive protein (CRP) and clinical scores.
In the group of adult CF patients, 24% were infected with SA but not PA. Patients with SA had lower frequencies of pulmonary exacerbations and CRP than ones with PA. This suggested that infection with SA is a marker of less severe disease. The authors did not identify significant correlation between the airway infection status and lung function, FEV 1 and FVC, which is the forced vital capacity. The authors compared patients with only PA and those with PA together with SA and found no significant differences in demographic or clinical parameters.
The study, like others, may have underestimated the true prevalence of SA infection. However, overall, it suggested that, unlike pediatric cases, the colonization of SA in adults with cystic fibrosis and without Pseudomonas aeruginosa infection is an indication of milder lung disease.