Journal: Am J Surg 194(8):606-610, 2007. 26 References
Reprint: Michael E. DeBakey Department of Surgery, Baylor College of Medicine, MED Veterans Affairs Hospital, OCL (112), 2002 Holcombe Blvd, Houston, TX 77030 (SS Awad, MD)
Faculty Disclosure: Abstracted by T. Tilton, who has nothing to disclose.
Methicillin-resistant Staphylococcus aureus (MRSA) infections are increasing alarmingly and have even become epidemic in some regions of the US. Since first described in 1961, the pathogens (HA-MRSA) were hospital-acquired and thought to be related to previous antibiotic exposure, prolonged hospital stay and patient comorbidities. A different MRSA pathogen was identified in the early 1990's in patients presenting from the community (CA MRSA) with different genetic and epidemiological markers. Syndromes associated with CA MRSA include: skin and soft tissue infections (SSTIs, such as furuncles, impetigo, cellulitis); bloodstream (bacteremia, endocarditis, line sepsis); lungs (pneumonia, empyema); bones and joints (osteomyelitis, septic arthritis) and urinary tract (pyelonephritis). Vancomycin has been the most commonly used pharmacologic intervention. Because of the high prevalence of MRSA as a cause of SSTIs, the authors examined the incidence of MRSA from 2000 2006 in surgical patients with SSTIs, the choice of empiric antibiotic therapy, and vancomycin minimum inhibitory concentration (MIC) in MRSA isolates.
Medical records of consecutive patients undergoing debridement of complicated SSTI infections over the 7-year study period were reviewed. A total of 288 patients were identified. Demographic data showed mean (± SD) age of 54±11, and comorbidities of smoking 55%, diabetes mellitus 52%, alcoholics 34%, and hepatitis C 23%; 67% of patients were ASA PS 3. Mean temperature on admission was 99.2º±1.5º F; WBC count 13.8±14.6; HgA1C for diabetics 8.6±2.5; creatinine 1.2±0.7; glucose 163±119; BUN 16±12. Intraoperative cultures most commonly grew S. aureus, of which 70% was MRSA; Streptococcus species accounted for only 15% of isolated microbes; 67% of cultures showed monomicrobial etiology of which MRSA was the predominant isolate from such cultures (68%).
MRSA frequency increased from 34% in 2000 to 77% in 2006. A total of 25% of patients had received (the week before admission) antibiotics as definitive treatment for their SSTI without incision and drainage but this did not correlate with the MRSA isolate. MRSA antimicrobial susceptibility showed 100% to vancomycin, 98% to trimethoprim sulfamethaxazole, and tetracycline 78%; a significant decrease to quinolones (61%); and a fluctuating susceptibility to clindamycin (63%); 15% and 4% of MRSA isolates were susceptible to erythromycin in 2000 and 2006, respectively (average 17%). Empiric therapy was adequate in 86% with vancomycin as the most common; frequency of empiric vancomycin administration increased from 18% in 2000 to 93% in 2006. Vancomycin MIC showed a shift for MRSA isolates with 38% having an MCI ≥1.
HA MRSA isolates have been more resistant to antibiotics than CA MRSA, likely because smaller staphylococcal chromosomal cassette (SCC; method for classifying MRSA as SCC contains genes that cause resistance), which makes CA MRSA less capable of carrying antimicrobial resistance genes. CA MRSA has been frequently associated with SSTIs, necrotizing fasciitis, and hemorrhagic necrotizing pneumonia and HA MRSA with nosocomial pneumonia, catheter-related urinary tract infections and bloodstream infections.
Minor SSTIs may be treated with incision and drainage alone; antibiotics should be reserved for patients with significant comorbidities or immunosuppression or who have recurrent infections. Severe SSTIs, especially with signs of systemic toxicity, require surgical debridement and antimicrobials. Vancomycin has been the most commonly used and most familiar to clinicians but its overuse has led to MRSA resistance to vancomycin (VRSA), leaving it as a suboptimal choice for SSTIs. Newer FDA approved antimicrobials include linezolid (71% clinical cure rate vs. 55.1% with vancomycin), daptomycin, and tigecycline.
The incidence of MRSA in patients with SSTIs is significantly increasing, and empiric coverage with an MRSA antimicrobial should be used as first-line therapy for severe SSTIs in patients undergoing surgical debridement. Vancomycin is becoming increasingly ineffective and alternative antimicrobials should be considered. |
