Necrotizing Soft Tissue Infections

Description

• Necrotizing soft tissue infections (NSTI) are infections of any layer of the skin associated with necrotizing changes
  • Usually spreads rapidly along tissue planes
• Characterized by:
  • Widespread fascial and muscle necrosis with relative sparing of the skin
  • High mortality
  • Systemic toxicity
• Crepitant anaerobic cellulitis:
  • Necrotic soft tissue infection with abundant connective tissue gas
• Progressive bacterial gangrene:
  • Slowly progressive erosion affecting the total thickness of skin but not involving deep fascia
• Nonclostridial myonecrosis (synergistic necrotizing cellulitis):
  • Aggressive soft tissue infection of skin, muscle, SC tissue, and fascia
• Fournier gangrene:
  • Mixed aerobic–anaerobic soft tissue necrotizing fasciitis of the skin of the scrotum and penis in men and the vulvar and perianal skin in women
• Necrotizing fasciitis:
  • Progressive, rapidly spreading infection with extensive dissection and necrosis of the superficial and deep fascia
• Accounts for 500–1,500 cases per year in US
• Often difficult to recognize
• Incidence increases with:
  • Age
  • Smoking
  • Chronic systemic disease:
    • Diabetes
    • Obesity
    • Peripheral vascular disease
    • Alcohol abuse
    • IV drug use
• 24–34% mortality
• Also high morbidity:
  • Amputations
  • Renal failure

Etiology

• Conditions that lead to the development of NSTIs:
  • Local tissue trauma with bacterial invasion
  • Local ischemia and reduced host defenses:
    • More frequently in diabetics, alcoholics, immunosuppressed patients, IV drug users, and patients with peripheral vascular disease
• Type I NSTI:
  • Polymicrobial
  • Anaerobic and aerobic
  • Include Fournier gangrene and Ludwig angina
  • After surgical procedures
  • Existing diabetes, peripheral vascular disease, chronic kidney disease, alcohol abuse
    • Compromised immune system
  • Represent 80% of NSTIs
  • Strep species are most common aerobes
    • Also staph, enterococci, and gram-negative rods
  • Bacteroides are most common anaerobes
• Type II NSTI:
  • Monomicrobial
  • Typically aerobic Streptococcus
  • Often young, healthy patients
  • Most common cause of “flesh eating” disease
  • Methicillin-resistant Staphylococcus aureus (MRSA) species are becoming more common
• Type III NSTI
  • Least common NSTI (<5%)
  • Rapidly progressive
  • Clostridial myonecrosis is an example
  • Usually following penetrating wounds or crush injuries
  • Also can be seen after black tar heroin injection, skin popping, intestinal surgery, obstetrical complications
• Bacteria involved include:
  • Group A β₂-hemolytic streptococcus (GABHS)
  • Group B streptococcus
  • Staphylococci
  • Enterococci
  • Bacillus
  • Pseudomonas
  • Escherichia coli
  • Proteus
  • Klebsiella
  • Enterobacter
  • Bacteroides
  • Pasteurella multocida
  • Clostridium sp.
  • Vibrio sp.
  • Aeromonas sp.
  • Fungi

• Neonates: Omphalitis and circumcision are predisposing factors.
• Risk factors for children:
  • Chronic illness
  • Surgery
  • Recent varicella infection (58-fold increased risk of GABHS NSTI)
  • Congenital and acquired immunodeficiencies