Description

• Necrotizing soft tissue infections (NSTI) are infections of any layer of the skin and soft tissue associated with necrotizing changes
  • Includes cellulitis, fasciitis, and myositis
  • Usually spreads rapidly along tissue planes
• Characterized as a group by:
  • Widespread fascial and muscle necrosis with relative sparing of the skin
  • High mortality
  • Systemic toxicity
• Necrotizing cellulitis:
  • Crepitus and gas of skin
  • Spares deeper structures
  • May lack systemic toxicity
• Necrotizing fasciitis:
  • Classic, historical name (and often inaccurate description) for most NSTIs
  • Progressive, rapidly spreading infection with extensive dissection and necrosis of the fascia and subcutaneous (SC) fat
  • Frequently spares skin and muscle initially
• Fournier gangrene:
  • Mixed aerobic–anaerobic NSTI of the perineum
• CDC reports 500–1,500 cases per yr in the U.S.
• Often difficult to recognize initially
• Risk factors include:
  • Advanced age
  • Chronic systemic disease:
    • Diabetes
    • Obesity
    • Peripheral vascular disease
    • Renal failure
  • Smoking
  • Alcohol abuse
  • IV drug abuse
  • Immunosuppression
  • Recent surgery
  • Traumatic wounds
• 14–40% mortality
• High morbidity:
  • Frequent need for amputations
  • Renal failure, cardiomyopathy, multisystem organ dysfunction

Etiology

• Conditions that lead to the development of NSTIs:
  • Most from local tissue trauma with bacterial invasion
  • Less frequently from local ischemia or nonpenetrating trauma and reduced host defenses as above
• Type I NSTI:
  • Polymicrobial, including at least 1 anaerobe
  • Anaerobic and aerobic bacteria
  • Includes Fournier gangrene
  • Seen more in elderly, those with underlying illnesses, or after recent surgery
  • Represent majority of NSTIs
  • Streptococcal species are most common aerobes
    • Also Staphylococcus, Enterococcus, Escherichia coli, Klebsiella
  • Bacteroides are most common anaerobes
• Type II NSTI:
  • Monomicrobial
  • Most commonly group A Streptococcus
  • Staphylococcus aureus including methicillin-resistant S. aureus (MRSA) second most common
  • Often young, healthy patients
  • Almost half with no skin portal of entry
  • Often no gas seen on imaging
  • Approximately half of group A strep vs Strep - group A strep is multiple places in the text and the rest are lower case cases associated with streptococcal toxic shock syndrome
  • Predisposing factors include skin injury, IV drug use, surgery, childbirth
• Type III NSTI:
  • Less common NSTI (<5%)
  • Rapidly progressive
  • Includes infections from Clostridium, Vibrio, Aeromonas, and gram-negative bacteria
  • Usually following penetrating wounds, crush injuries, or aquatic exposure
• Type IV NSTI: (Rare)
  • Fungal etiology including Candida and Zygomycetes
  • Occurs in immunocompromised
• Microbes involved include:
  • Group A β-hemolytic Streptococcus (GABHS)
  • Group B Streptococcus
  • Staphylococcus
  • Enterococcus
  • Bacillus
  • Pseudomonas
  • E. coli
  • Proteus
  • Klebsiella
  • Enterobacter
  • Bacteroides
  • Pasteurella
  • Clostridium
  • Vibrio vulnificus
  • Aeromonas hydrophila
  • Candida
  • Zygomycetes

• Risk factors for neonates:
  • Omphalitis
  • Minor surgeries: Circumcision, hernia
• Risk factors for children:
  • Chronic illness
  • Surgery
  • Recent varicella infection
  • Congenital and acquired immunodeficiencies