BACKGROUND: We describe the clinical characteristics and epidemiology of 
methicillin-resistant Staphylococcus aureus (MRSA) in children with cystic 
fibrosis (CF) from the U.S. CF center with the highest MRSA prevalence.
METHODS: Medical records of children with CF were retrospectively reviewed from 
1997-2009. MRSA clinical isolates from 2007-2009 were analyzed by polymerase 
chain reaction and pulsed field gel electrophoresis.
RESULTS: The prevalence of MRSA was 1% in 1997 and 49% in 2009. Fifty-five 
children (26%) had persistent MRSA infection. Sixty-eight percent of MRSA 
isolates were hospital-associated (HA) MRSA, of which 52% were pulsed-field type 
USA 100. Ninety-three percent of HA MRSA isolates were clindamycin resistant. 
Twelve children acquired MRSA before 1 year of age, 83% of whom were 
hospitalized prior to acquisition of MRSA. Ten of 11 sibling pairs carried 
indistinguishable MRSA strains. Children with persistent MRSA were hospitalized 
more often (P = .01), required inhaled medications more frequently (P = .01), 
and had higher rates of Pseudomonas aeruginosa coinfection (P < .001).
CONCLUSION: MRSA prevalence in children with CF is increasing, and most children 
are infected with HA MRSA. Exposure to health care facilities and 
gastrointestinal surgeries may facilitate early acquisition of MRSA. Siblings 
carry indistinguishable MRSA strains, indicating household transmission of MRSA. 
Children with persistent MRSA had worse pulmonary morbidity. Coinfection with 
MRSA and P aeruginosa is likely associated with further increased pulmonary 
morbidity.