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Staphylococcus aureus septic arthritis caused by USA300 may be linked to longer duration of fever

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More than a third of patients with Staphylococcus aureus septic arthritis at the Texas Children’s Hospital had community-associated USA300 isolates and researchers believe the genotype may be associated with longer durations of fever.

“Empirical treatment of [septic arthritis] should include MRSA,” the researchers wrote.

They identified 45 children with S. aureus septic arthritis from August 2001 to October 2008. Among 44 isolates, 16 were identified as MRSA. Of those 16 isolates, 13 were USA300 and 14 were positive for Panton-Valentine leukocidin (PVL) genes. There were 28 MSSA isolates, of which eight were USA300 and 13 were positive for PVL.

Osteomyelitis was the most commonly reported associated infection site (n=14). Bacteremia lasting from 1 to 5 days was observed in 31% of the children.

Among children with associated osteomyelitis, increased likelihood of bacteremia (P=.001), fever >2 days (P=.03) and C-reactive protein levels ≥10 mg/dL (P=.01) were observed.

Children with infections caused by USA300 experienced fever for a median of four days (range, 0-15 days) compared with a one day median fever observed in children who had non-USA300 infections (range, 0-8 days; P=.03).

PVL was observed in 61% of the infections. C-reactive protein levels ≥10 mg/dL were more frequently observed in children with PVL-positive isolates compared with children who had PVL-negative isolates (P=.05).

Bacteremia, C-reactive protein levels ≥10 mg/dL and fever >2 days may be indicators of associated osteomyelitis, according to the researchers. They recommend monitoring antibiotic resistance rates within the community when choosing empiric therapy for S. aureus septic arthritis.

Carrillo-Marquez et al. Pediatr Infect Dis J. 2009;28:1076-1080.

Both Methicillin-susceptible and Methicillin-resistant S. aureus (community-associated or acquired-CA) are important pathogens causing acute septic arthritis in children. Thus, initial empiric therapy of suspected septic arthritis in children should include an antibiotic effective against community-associated strains of MRSA.

The USA300 clone accounted for almost all of the CA-MRSA isolates and almost 30% of the MSSA isolates. We found some association with the presence of the genes encoding for the Panton-Valentine leukocidin and the presence of cellulitis and soft tissue abscess in children with septic arthritis.

Fourteen of 45 patients (almost a third) had a contiguous site of osteomyelitis. We found that after therapy is initiated, a fever lasting more than 2 days, a C-reactive protein concentration >10 mg/dl anytime during the infecton or S. aureus bacteremia should increase the clinician's awareness for the possibility of a concomitant osteomyelitis.

- Sheldon Kaplan, MD

Head, Department of Medicine, Texas Children's Hospital