Association between respiratory tract methicillin-resistant Staphylococcus aureus and survival in cystic fibrosis

Context: The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in the respiratory tract of individuals with cystic fibrosis (CF) has increased dramatically; however, its impact on outcomes in CF is unclear. Because the time between infection with bacteria in CF and death can be decades, observational studies with long periods of follow-up are well suited to address the current gap in knowledge. Objective: To determine whether isolation of MRSA from the respiratory tract of CF patients is associated with worse survival compared with patients who never have a culture positive for MRSA. Design, Setting, and Participants: Cohort study of 19 833 CF patients aged 6 to 45 years seen at centers accredited by the Cystic Fibrosis Foundation in the United States. Patients entered between January 1996 and December 2006 and were followed up through December 2008. Cox regression models with time-varying covariates were used to compare survival between CF patients with and without respiratory tract MRSA. Main Outcome Measure: Time from age at entry until age at death from any cause. Results: In 137 819 patient-years of observation (median, 7.3 years/patient), 2537 CF patients died and 5759 patients had MRSA detected. The mortality rate was 18.3 deaths (95% confidence interval [CI], 17.5-19.1) per 1000 patient-years in patients without MRSA and 27.7 deaths (95% CI, 25.3-30.4) per 1000 patient-years in those with MRSA. Among those with MRSA, the attributable risk percentage of death associated with MRSA was 34.0% (95% CI, 26.7%-40.4%). The unadjusted hazard ratio associated with MRSA was 1.47 (95% CI, 1.32-1.62). After adjustment for timevarying covariates associated with severity of illness, MRSA remained associated with a higher risk of death (1.27; 95% CI, 1.11-1.45). Conclusion: Detection of MRSA in the respiratory tract of CF patients was associated with worse survival.