Background: Methicillin-resistant Staphylococcus aureus (MRSA) infection typically occurs in
chronically ill patients requiring long-term antimicrobial therapy or hospitalization. However,
community-associated MRSA (CA-MRSA) necrotizing soft tissue infections seem to be
increasing in incidence. Our aim was to describe the incidence and microbiologic characteristics
of CA-MRSA isolates collected at an army community hospital.
Methods: We report a retrospective review of MRSA isolates identified during 1998–2003
at the microbiology laboratory of Moncrief Army Community Hospital that serves a community
of approximately 40,000 transient residents yearly in Fort Jackson, South Carolina. We
evaluated the incidence of MRSA in our laboratory during 1998–2003. For MRSA isolates from
2003, we evaluated antimicrobial susceptibility patterns. Six selected isolates were evaluated
by molecular typing, resistance gene analysis, and toxin analysis.
Results: During 1998–2003, 241 (23%) of 1041 S. aureus isolates identified at the hospital microbiology
laboratory were resistant to methicillin. Of these 241 MRSA isolates, 223 were cultured
from outpatients. The incidence of MRSA in our population increased from 12% of S.
aureus isolates in 1998 to 43% in 2003. In 2003, MRSA was cultured from 76 different patients.
Isolates of MRSA were often resistant to erythromycin (91%), although resistance to other
agents was less common: Ciprofloxacin (14%), levofloxacin (14%), clindamycin (3%), tetracycline
(3%), and trimethoprim sulfamethoxazole (1%). No isolates were resistant to vancomycin,
gentamicin, nitrofurantoin, or rifampin. Six CA-MRSA isolates were compared by pulsedfield
gel electrophoresis (PFGE). Five were PFGE type USA300, and one was PFGE type
USA100, based on the U.S. Centers for Disease Control and Prevention (CDC) classification
scheme. The five USA300 isolates carried SCCmec type IV, and the USA100 carried SCCmec
II. None of the isolates were positive by PCR for genes encoding enterotoxins A–E and H, or
toxic shock syndrome toxin (TSST-1), but the five USA300 isolates carried the gene coding
for Panton-Valentine leukocidin toxin.
Conclusions: The incidence of MRSA at our institution is increasing. Isolates of MRSA show
resistance patterns and microbiologic characteristics consistent with CA-MRSA isolates from
the United States. Clinicians should consider the possibility of CA-MRSA in patients with softtissue
infections who do not respond to initial therapy with beta-lactam antimicrobial agents.
