New developments in staphylococcal infections

This week’s NEJM reports a study from the S. aureus Endocarditis and Bacteremia Study Group showing non-inferiority of daptomycin (Cubicin) compared with “standard” therapy (vancomycin or an antistaphylococcal penicillin for MRSA or MSSA, respectively, both initially combined with low dose gentamicin) in patients with Staphylococcus aureus bacteremia and right sided endocarditis. Acquired resistance to daptomycin occurred leading to treatment failure, counterbalanced by increased renal toxicity causing treatment interruption in the standard therapy group, also contributing to treatment failure.

In the same issue is a report from Moran and colleagues on the microbiology and clinical characteristics of skin and soft tissue infections (classified as abscess, wound infection or cellulitis) presenting to emergency departments across a wide swath of the U.S. The majority of isolates were MRSA which possessed characteristics unique to community associated MRSA (CA-MRSA) including expression of the Panton-Valentine leukocidin toxin (PVL) and the characteristic sensitivity pattern.

An editorial in the same issue makes these points about the two studies:

1) When oral antibiotic therapy is indicated, trimethoprim-sulfamethoxazole (TMP-SMX) may be a reasonable choice for CA-MRSA but it is not effective against streptococci. Clindamycin is effective against streptococci but CA-MRSA may exhibit inducible clindamycin resistance. (This Mayo Clinic Proceedings review suggests combining TMP-SMX or a tetracycline with a beta lactam such as cephalexin to get around the problem).
2) Abscesses should be incised and drained and, given somewhat variable sensitivity patterns, culture data should guide therapy.
3) Daptomycin is an alternative to older standard therapy for bacteremia. Emergence of resistance during treatment is a problem. Patients who appear to fail treatment should be evaluated for acquired resistance to daptomycin in addition to sequestered foci of infection. (Daptomycin is not recommended for treatment of pneumonia).

DB weighs in with a discussion of how the problem is handled at his institution.