Necrotizing soft tissue infection

Background

See Classification, below
Most commonly caused by monomicrobial Streptococcus pyogenes, Staphylococcus aureus, Clostridium, or Vibrio, or polymicrobial infections that include Gram-positives, Gram-negatives, and anaerobes

Although it is classically divided into Type 1 (polymicrobial) and Type 2 (monomicrobial), others have proposed an extension to include Type 3 (water-associated monomicrobial) and Type 4 (fungal).
Type 1: polymicrobial, including Staphylococcus aureus, Gram-negative bacilli, and anaerobes
Type 2: monomicrobial Gram-positive infections, primarily Streptococcus pyogenes (most common) but also Staphylococcus aureus or Clostridium (penetrating trauma, soil exposure)
Type 3: monomicrobial Gram-negative infections, generally caused by water-associated Vibrio vulnificus or Aeromonas hydrophila
Type 4: fungal, caused by Candida species, and exceedingly rare

Surgical debridement!
Empiric antibiotics
- Piperacillin-tazobactam 4.5 g IV q8h (or, alternatively, meropenem)
- Clindamycin 600 to 900 mg IV q8h, for synergy and the Eagle phenomenon and decreased toxin production
- If risk for MRSA, add vancomycin 15-20 mg/kg IV q8-12h
- If water exposure, add two of: a fluoroquinolone, a carbapenem, a third-generation cephalosporin, and/or doxycycline (should have double-coverage pending susceptibilities)
- Some recommend replacing clindamycin (and possibly vancomycin) with linezolid1
Then narrow based on the Gram stain an culture
Can consider IVIg, rarely, in streptococcal or staphylococcal toxic shock syndrome

Originally, referred to decreased effectiveness of penicillins at high concentrations
Now, refers to decreased effectiveness of penicillins at high bacterial burden (when in stationary phase)
Clindamycin kills enough of the bacteria that are in stationary phase that the bacteria return to logarithmic growth phase, where penicillins are more effective