Anaerobic and Necrotizing Infections



  • Necrotizing soft tissue infections (NSTI) are rare and rapidly progressing infections involving any layer of soft tissue, including skin, subcutaneous fat, fascia, and/or muscle (1).
  • NSTI can affect any part of the body but are more commonly seen in extremities and abdominal wall (1).
  • NSTI are associated with extensive tissue destruction, systemic toxicity, limb loss and are potentially fatal.
  • NSTI represent a medical emergency. Early diagnosis, prompt surgical consultation, and initiation of broad-spectrum antibiotics are essential in improving outcomes (2).
  • Associated terms: necrotizing fasciitis, progressive bacterial synergistic gangrene, synergistic necrotizing cellulitis, gas gangrene, nonclostridial anaerobic cellulitis, Fournier gangrene, Ludwig angina, “flesh-eating” infections


  • Predominant age: any age
  • Predominant sex: male = female


  • 4 per 100,000
  • Increased incidence in patients >50 years

Etiology and Pathophysiology

  • Type I NSTI—most common
    • Polymicrobial, typically a combination of aerobic and anaerobic species (1)
    • More common in patients with specific risk factors (see below), although no specific inciting event is identified in 20–50% of patients (3)
  • Type II NSTI
    • Monomicrobial infection
    • Tends to occur in otherwise healthy individuals (3)
    • Most commonly caused by group A β-hemolytic streptococci (Streptococcus pyogenes), followed by methicillin-resistant Staphylococcus aureus (MRSA) (2)
  • Type III NSTI
    • Vibrio vulnificus—associated with exposure to marine environments, especially in patients with severe liver disease
    • Aeromonas hydrophila—associated with exposure to freshwater environments
    • Clostridium perfringens
  • Bacteria enter the soft tissue after trauma causing skin or mucosal breach. Bacterial invasion may also occur without definite site of entry in a host with transient bacteremia after deep tissue trauma (2).
  • Bacterial toxins and surface proteins cause a local inflammatory response. Vascular occlusion follows leading to deep tissue ischemia and necrosis (2).
  • Bacterial toxins may trigger a systemic inflammatory response, leading to multiorgan failure or sepsis (2).

Risk Factors

  • Can occur in young, healthy persons without risk factors
  • Predisposing risk factors (3)
    • Advanced age
    • Obesity
    • Diabetes, cirrhosis, end-stage renal failure
    • Malnutrition
    • Immune suppression (HIV, malignancies, alcoholism, corticosteroid use)
    • History of cellulitis or impaired venous and lymphatic drainage (4)
    • Peripheral vascular disease
  • Precipitating risk factors
    • IV drug abuse
    • Trauma, burns
    • Skin ulceration
    • Herpes zoster
    • Human, animal, or insect bites (4)
  • Surgical risk factors
    • Prior operations
    • Hypoalbuminemia

General Prevention

  • Management of predisposing risk factors (4)
  • Diabetics should have regular foot examinations (4).
  • Appropriate wound care after trauma involving irrigation, foreign body removal, and débridement of devitalized tissue (4)
  • Sterile surgical procedures and skin closure (2)

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