Prevalence and impact on FEV(1) decline of chronic methicillin-resistant Staphylococcus aureus (MRSA) colonization in patients with cystic fibrosis. A single-center, case control study of 165 patients

BACKGROUND: Risk factors for methicillin-resistant Staphylococcus aureus (MRSA) in Cystic Fibrosis (CF) and the impact on CF disease progression are still under debate. The objectives of this study were to determine clinical variables associated with MRSA colonization and examine impact on FEV(1) evolution in CF patients.

METHODS: A retrospective case-control study using the University Hospital of Brussels CF clinic patient registry from 2002 to 2010, comparing clinical variables and decline of FEV(1) of MRSA positive patients with age and sex matched controls, chronically colonized with S. aureus.

RESULTS: Thirty of the 165 CF patients, chronically colonized with S. aureus, had cultures positive for MRSA (18.2%). Excluding patients under 4 years, the prevalence became 15.2% (23/151). Chronic colonization (i.e., three or more consecutive positive cultures) was found in 19/151 (12.6%). The MRSA positive group showed a higher proportion of patients with genotype F508del, less pancreas sufficient patients, more bronchiectasis and more frequent hospitalization. The FEV(1) recorded one year prior to, and at the moment of MRSA acquisition, was lower but not significantly different from that obtained in controls (72.9%±26.6 vs 84.3±21.8 and 68.2%±27.1 vs 81.4%±24.3 respectively, p>0.1). However, FEV(1) decline over 2- and 6-year periods, were significantly greater in the chronic MRSA group than in the controls (-5%±5.5 vs -2.5±2.3 over 2 years (p=0.043) and -1.8%±4.6 vs -1.0%±1.9 over a 6-year period (p=0.026)).

CONCLUSION: In our center the prevalence of MRSA in CF patients, chronically colonized with S. aureus and over the age of 4 years, was 15.2% (12.6% chronic infection). MRSA colonization was shown to be associated with a genotype F508del, presence of bronchiectasis and hospitalization. Our spirometric data also show that a MRSA episode entails an FEV(1) decline that is almost double that predicted for CF patients who can remain unaffected by MRSA.