1. Home>
2. Specialties>
3. Infectious Diseases>
4. Summary and Comment

Staphylococcal Infections — From the Surface to the Depths

The strain responsible for most MRSA skin and soft-tissue infections is sensitive to many antimicrobials; daptomycin may be an alternative for systemic staph infections.

Methicillin-resistant Staphylococcus aureus (MRSA), traditionally one of our most formidable nosocomial bacterial foes, is now a common cause of community-acquired skin and soft-tissue infections. Meanwhile, staphylococci have retained their prominence as causative agents in difficult-to-treat systemic bacteremic disease. Two new studies address prevalence and treatment of staph infections.

Moran and colleagues conducted a multicenter, prospective investigation involving 422 adults with skin and soft-tissue infections who presented in August 2004 at any of 11 emergency departments participating in the EMERGEncy ID Net. S. aureus was the causative agent in 320 patients (76%); MRSA accounted for 78% of S. aureus isolates and was the most common identifiable agent in 10 of the 11 centers. Pulsed-field gel electrophoresis of 218 MRSA isolates revealed that 99% had a community-acquired phenotype and 97% belonged to a single type (USA300). Furthermore, 72% of them were of one strain (USA300-0114), and almost all carried the Panton-Valentine leukocidin toxin gene and type IV SCCmec. USA300 was also the most common pulsed-field type among methicillin-sensitive S. aureus (MSSA) isolates. MRSA isolates were sensitive to trimethoprim-sulfamethoxazole (100%), rifampin (100%), clindamycin (95%), tetracycline (92%), fluoroquinolones (60%), and erythromycin (6%). Treatments included incision and drainage alone or with antibiotics, or antibiotics alone; 5% of patients received none of these interventions. Antimicrobial treatment of MRSA was concordant with in vitro sensitivities in only 43% of cases, but outcome was good with all treatment modalities including no treatment.

In an industry-funded, multinational, open-label, noninferiority trial, Fowler and colleagues compared intravenous daptomycin (a cyclic lipopeptide; 6 mg/kg daily) with traditional antimicrobial treatment (initial low-dose gentamicin plus either a penicillinase-resistant ß-lactam or vancomycin) in 236 patients with deep-seated MRSA or MSSA infections. Twenty-three percent of these patients had endocarditis by modified Duke criteria, and 77% had bacteremia. Forty-two days after the end of therapy, 44% of daptomycin recipients and 42% of standard-therapy recipients had "successful" outcomes, as determined by blood cultures and clinical criteria. The authors concluded that daptomycin is not inferior to standard antibiotic therapy for treatment of S. aureus bacteremia and right-sided endocarditis caused by MSSA or MRSA. Treatment failure with daptomycin often was associated with emergence of daptomycin-resistant organisms.

Comment: Fortunately, the MRSA most commonly responsible for superficial infection is sensitive to many antimicrobials. However, as an editorialist points out, if surgical drainage of such infections is possible, antibiotic treatment is of secondary importance and may be unnecessary. Good outcomes despite lack of sensitivity and treatment concordance support this notion. Although in the second study daptomycin was shown to be "not inferior" to standard therapy in systemic staph infection, this trial had many shortcomings, including an open-label design, a very poor cure rate (especially for endocarditis) in both study arms, a very heterogeneous disease population, and little or no description of other modalities (e.g., surgery) that might be unequally distributed and be essential for cure. Perhaps this regimen would be useful in penicillin-allergic patients with MSSA bacteremia.

— Stephen G. Baum, MD

Published in Journal Watch Infectious Diseases August 16, 2006

Citation(s):

Moran GJ et al. Methicillin-resistant S. aureus infections among patients in the emergency department. N Engl J Med 2006 Aug 17; 355:666-74.

• Original article (Subscription may be required)
• Medline abstract (Free)

Fowler VG Jr et al. Daptomycin versus standard therapy for bacteremia and endocarditis caused by Staphylococcus aureus. N Engl J Med 2006 Aug 17; 355:653-65.

• Original article (Subscription may be required)
• Medline abstract (Free)

Grayson ML. The treatment triangle for staphylococcal infections. N Engl J Med 2006 Aug 17; 355:724-7.

• Original article (Subscription may be required)
• Medline abstract (Free)