The impact of incident methicillin resistant Staphylococcus aureus detection on pulmonary function in cystic fibrosis

The incidence of methicillin resistant Staphylococcus aureus (MRSA) infection is increasing in cystic fibrosis (CF), but the impact of MRSA detection on clinical outcomes is unclear. Our objective was to determine whether incident detection of MRSA is associated with a change in pulmonary function over time in CF patients. We analyzed data from the Epidemiologic Study of Cystic Fibrosis (ESCF), a prospective observational study of CF patients in North America. Multivariable piecewise linear regression was used to model the impact of incident detection of MRSA on pulmonary function over time, measured by percent predicted forced expiratory volume in one second (FEV(1)% predicted), adjusting for potential confounders. There were 5,090 patients >or=6 years old who were MRSA negative for at least 2 calendar years. Five hundred ninety-three (12%) of these patients acquired MRSA during the years 2001-2003, with detection rates of MRSA during those years rising from 4.4% to 6.9%. MRSA positive patients had a lower FEV(1)% predicted and received more antibiotic and other therapies than patients who remained MRSA negative. After adjusting for antibiotic therapy and other potential confounders, MRSA positive patients also had a higher rate of decline in FEV(1)% predicted both before and after the incident culture, although the rate of FEV(1)% predicted decline did not change significantly after MRSA detection. In conclusion, although MRSA in CF was a marker for more aggressive therapy and may reflect increased disease severity, incident MRSA detection was not associated with a changing rate of FEV(1)% predicted decline.