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Complex Molecular Epidemiology of Methicillin-Resistant Staphylococcus aureus (MRSA) Isolates from Children with Cystic Fibrosis in the Era of Epidemic Community-Associated MRSA

¹From the Department of Pediatrics, Sections of Infectious Diseases and Pulmonary Medicine ³, University of Chicago, Chicago, Illinois, and the Department of Pediatrics, University of Texas Southwestern Medical Center ², Dallas, Texas

rdaum{at}peds.bsd.uchicago.edu

Abstract

Background: Limited data exist about the molecular types of MRSA strains found in children with CF. We sought to characterize MRSA strains from these patients and compare them with MRSA strains from non-CF pediatric patients.

Methods: All MRSA isolates were collected prospectively at Children's Medical Center in Dallas and University of Chicago Children's Hospital in 2004-5. All CF MRSA isolates underwent susceptibility testing, multilocus sequence typing (ST), Panton-Valentine leukocidin gene detection (pvl+) and staphylococcal chromosome cassette mec (SCCmec) typing.

Results: 22/34 (64.7%) MRSA isolates from patients with CF belonged to clonal complex (CC) 5 and contained SCCmec II, so-called health care associated (HA) MRSA strains. 11/34 (32.4%) were CC 8, and contained SCCmec IV, so-called CA-MRSA strains. The CA-MRSA strains tended to be isolated from newly colonized CF patients. In contrast, CC 8 isolates predominated among non-CF patients (300/331, 90.6%). MRSA isolates from children with CF were more likely to be resistant to clindamycin (65% vs. 26%) and ciprofloxacin (62% vs. 17%) compared with strains from non-CF patients, p<0.001. There was no difference in the rate of pvl+ isolates recovery from children with CF receiving surveillance cultures (7/23) compared with those with pulmonary exacerbation (3/11), p=1.0.

Conclusions: Both CA-MRSA (CC8) and HA-MRSA (CC5) isolates populate the respiratory tracts of children with CF. HA-MRSA isolates predominated, but CA-MRSA strains predominated among CF patients with newly acquired MRSA strains and among the non-CF patients. CA-MRSA strains of children with CF were not associated with exacerbation or necrotizing pneumonia.

Key Words: Cystic Fibrosis • Children • Methicillin-Resistant Staphylococcus aureus • Molecular epidemiology