Emergence of community-associated methicillin-resistant Staphylococcus aureus USA 300 clone as a cause of health care-associated infections among patients with prosthetic joint infections

Abstract

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has emerged as an important cause of staphylococcal infections, but there have been little data on whether CA-MRSA causes health care-associated infections. A case-control study was performed to identify risk factors for prosthetic joint infections (PJI). Antibiograms of isolates associated with PJI were reviewed. Molecular typing of available MRSA isolates was done using pulsed field gel electrophoresis (PFGE). Nares cultures of health care workers who provided care to those orthopedic patients were obtained. Over a 13-month period (January 2003-January 2004), 9.5% of patients with prosthetic hip (THA) or knee (TKA) joint surgery developed PJI (7 TKA and 2 THA). The mean time to development of PJI was 20 days. Five infections were caused by CA-MRSA and 3 by methicillin-susceptible S aureus; one was culture negative. All CA-MRSA isolates had identical antibiograms (resistant to beta-lactams and erythromycin; susceptible to clindamycin, trimethoprim-sulfamethoxazole, rifampin, gentamicin, levofloxacin, and vancomycin). Molecular typing of 2 available CA-MRSA isolates revealed that these were the USA300 clone; these isolates were PVL+ and carried SCCmec IV. CA-MRSA was not recovered from nares cultures from 31 health care workers. In multivariate analysis, TKA (OR, 8.1; 95% CI: 1.3-48.1) and surgery time >180 minutes (OR, 7.4; 95% CI: 1.4-39.6) were associated with PJI. We have demonstrated that the CA-MRSA USA300 clone is no longer just a cause of community-acquired infections but has also emerged as a cause of health care-associated infections, causing PJI at our institution.