Outcomes and Treatment of Chronic Methicillin-Resistant Staphylococcus aureus Differs by Staphylococcal Cassette...

Methicillin-resistant Staphylococcus aureus (MRSA) infects ∼25% of patients with cystic fibrosis (CF) in the United States. We hypothesized that health-related outcomes differed between healthcare-associated (staphylococcal cassette chromosome mec [SCCmec] II) vs community-associated (SCCmec IV) MRSA strains in patients chronically infected with CF.

At 7 CF centers, MRSA isolates were prospectively obtained from patients ≤18 years old with 2 or more positive MRSA cultures within 1 year. Isolates were classified by SCCmec type and Panton-Valentine-leukocidin (PVL) status at a core laboratory, and sites remained blinded to SCCmec type and PVL results. Prospective clinical data including antibiotic use, respiratory symptoms, and pulmonary exacerbations were obtained.

Among the 295 cohort participants with typeable MRSA isolates, 69.5% had SCCmec II PVL(-), 13.2% had SCCmec IV PVL(-), and 17.3% had SCCmec IV PVL(+) strains. During follow-up of 287 patients with prospective data after enrollment, the risk for pulmonary exacerbations was significantly higher among participants with SCCmec II than SCCmec IV strains (risk ratio [RR] = 1.13; P = .03) and higher in those with SCCmec IV PVL(-) than SCCmec IV PVL(+) strains (RR = 1.62; P < .0001). Neither decline in lung function nor changes in nutritional outcomes differed by SCCmec type or PVL status during the study period.

Participants harboring chronic SCCmec II MRSA received more antibiotics and may have more lung disease than those with SCCmec IV; PVL(+) isolates were not associated with more advanced disease.