Background:

Methicillin-resistant Staphylococcus aureus (MRSA) USA300 is a predominant cause of community-acquired (CA) infection in the United States. We compared clinical characteristics of children with USA300 versus non-USA300 CA-methicillin-susceptible S. aureus (CA-MSSA) invasive infections at Texas Children's Hospital (TCH).

Methods:

Medical records were reviewed from children with invasive CA-MSSA infections at TCH between August 1, 2001 and September 30, 2006. Isolates were characterized by pulsed-field gel electrophoresis and polymerase chain reaction for Panton-Valentine leukocidin genes (pvl).

Results:

Invasive CA-MSSA infections increased from 14 in year 1 to 36 in year 5 (5-year total= 122 patients). Among the CA-MSSA isolates available for typing in the 5-year period, USA300 MSSA strains increased from 14%(2 of 14) to 35%(11 of 31)(P= 0.03). USA300 MSSA strains were more likely than non-USA300 MSSA strains to be nonsusceptible to erythromycin [66%(19 of 29) versus 28%(25 of 88); P< 0.01]. Osteomyelitis cases increased from 43%(6 of 14) in year 1 to 67%(24 of 36) in year 5. The majority of pvl+ MSSA isolates were USA300 (71%(25 of 35); only 5%(4 of 82) of pvl− MSSA isolates were USA300. Patients with osteomyelitis caused by pvl+ isolates had significantly higher mean values for erythrocyte sedimentation rate at admission (P= 0.005) and erythrocyte sedimentation rate maximum value (P= 0.002), maximum C-reactive protein (P= 0.04), and absolute neutrophil count at presentation (P= 0.04) compared with patients whose isolates were pvl−.

Conclusions:

USA300 accounted for a growing proportion of CA-MSSA isolates among children and was associated with increased numbers of invasive CA-MSSA infections at TCH, especially osteomyelitis. Associations were found in CA-MSSA osteomyelitis between pvl and increased concentrations of systemic inflammatory markers in patients.