Necrotizing soft tissue infection

Background

Microbiology

• 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

Classification

• 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

Management

• 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 linezolid
• Then narrow based on the Gram stain an culture
• Can consider IVIg, rarely, in streptococcal or staphylococcal toxic shock syndrome

Eagle Effect

• 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

Further Reading

• RCT of IVIG: Madsen MB et al. Immunoglobulin G for patients with necrotising soft tissue infection (INSTINCT): a randomised, blinded, placebo-controlled trial. Intensive Care Med. 2017;43:1585-93.