USA300 is the predominant genotype causing staphylococcus aureus septic arthritis in children

Background: Staphylococcus aureus is the most common cause of septic arthritis (SA) in children. USA300 is the predominant community methicillin-resistant (MRSA) clone. Panton-Valentine leukocidin genes (pvl) have been associated with severe disease. Methods: Patients with S. aureus SA were identified from the Texas Children's Hospital surveillance study. Pulsed field gel electrophoresis and pvl polymerase chain reaction were performed on isolates. Results: Forty-five patients with S. aureus SA were identified between August 2001 and October 2008. Median age was 5.5 years (0.3-17.9 years); 69% were previously healthy. The most common joints affected were hip (40%) followed by knee (36%). Associated infection sites were osteomyelitis (n = 14), pyomyositis/myositis (n = 13), and cellulitis (n = 9). Bacteremia for 1 to 5 days occurred in 31% of the patients. Patients with associated osteomyelitis were more likely to be bacteremic (P = 0.001), have fever >2 days (P = 0.03), and to have C-reactive protein (CRP) ≥10 mg/dL (P = 0.01). Of 44 available isolates, 16 were MRSA; 13 of 16 were USA300 and 14 of 16 were pvl+. Twenty-eight isolates were MSSA; 8 of 28 were USA300 and 13 of 28 were pvl+. Infections caused by USA300 isolates were associated with longer duration of fever than non-USA300 isolates (median, [range]: 4 [0-15] days vs 1 [0-8] days) (P = 0.03). Overall, 61% of the isolates were pvl+. CRP ≥10 mg/dL was more likely in pvl+ infections than in pvl-infections (P = 0.05). Conclusions: S. aureus SA caused by USA300 isolates is associated with longer duration of fever. Empirical treatment of SA should include MRSA. CRP levels ≥10 mg/dL, fever >2 days, and bacteremia should raise suspicion for associated osteomyelitis.