In a new study entitled “Clinical outcomes associated with Staphylococcus aureus and Pseudomonas aeruginosa airway infections in adult cystic fibrosis patients,” the authors determined the prevalence of Staphylococcus aureus infection in adult patients with cystic fibrosis and how this type of infection determines patients’ clinical outcomes. The study was published in the journal BMC Pulmonary Medicine.

Cystic Fibrosis (CF) is caused by mutations in a specific gene, the Cftr gene (short for cystic fibrosis transmembrane conductance regulator). The CFTR protein is a key regulator of chloride and sodium ions, which are transported in and out of cells within lungs and the intestinal epithelium. In the absence of CFTR functional protein, thick mucus accumulates in the lungs, making CF patients more susceptible to infections.

Staphylococcus aureus (SA) is the primarily organism that infects CF patients (is in fact the first and second most prevalent organism found in the respiratory tract of CF children and adults, respectively). However, while the outcome of infection in CF children is well documented (SA is associated with pulmonary inflammation and decline in lung function), the clinical outcome in CF adults is under-investigated.

In this new study, authors performed a retrospective cross-sectional study and investigated the link between the microbial species present in the respiratory tract of CF adults, particularly the presence of SA and Pseudomonas aeruginosa (PA), and lung function (measured with Forced expiratory volume in 1 second, FEV1, which measures the volume exhaled during the first second of a forced expiratory maneuver, beginning from the level of total lung capacity). Additionally, the team determined other parameters, including plasma C-reactive protein (CRP, a marker of inflammation) and clinical outcomes. The study was performed with collected data of adult CF patients (aged at least 18 years old) from the Montreal Chest Institute, Canada.

In the cohort of adult patients (84 in total) the authors found that 24% of patients are colonized with SA only and were negative for the presence of PA. The team observed that the SA-exclusive CF adult patients associated with lower rates of pulmonary exacerbations and CRP when compared to those positive for PA. They found that 60% of the patients were infected with PA and that 16% of the patients tested negative for both SA and PA infections. Notably, authors did not observe any link between lung function and the infection status of patients’ airways.

In light of their results, authors suggest that infection with SA is a marker of less severe disease, and while in children SA infection is associated with a decline in lung function, in adults, SA infections in the absence of PA is a marker of mild disease.