Persistent methicillin-resistant Staphylococcus aureus and rate of FEV1 decline in cystic fibrosis

Rationale: The prevalence in cystic fibrosis (CF) of respiratory cultures with methicillin-resistant Staphylococcus aureus (MRSA) has dramatically increased over the last 10 years, but the effect of MRSA on FEV1 decline in CF is unknown. Objectives: To determine the association between MRSA respiratory infection and FEV1 decline in children and adults with CF. Methods: This was a 10-year cohort study using the Cystic Fibrosis Foundation patient registry from 1996-2005. We studied individuals who developed new MRSA respiratory tract infection. Repeated-measures regression was used to assess the association between MRSA and FEV1 decline, adjusted for confounders, in individuals aged 8-21 years and adults (aged 22-45 yr). Two different statistical models were used to assess robustness of results. Measurements and Main Results: The study cohort included 17,357 patients with an average follow-up of 5.3 years. During the study period, 1,732 individuals developed new persistent MRSA infection (>= 3 MRSA cultures; average, 6.8 positive cultures) and were subsequently followed for an average of 3.5 years. Even after adjustment for confounders, rate of FEV1 decline in individuals aged 8-21 years with persistent MRSA was more rapid in both statistical models. Their average FEV1 decline of 2.06% predicted/year was 43% more rapid than the 1.44% predicted/year in those without MRSA (difference, -0.62% predicted/yr; 95% confidence interval, -0.70 to -0.54, P < 0.001). Effect of MRSA on FEV1 decline in adults was not clinically significant. Conclusions: Persistent infection with MRSA in individuals with CF between the ages of 8 and 21 years is associated with a more rapid rate of decline in lung function.