Necrotizing Soft Tissue Infections

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Basics

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

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

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Basics

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

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

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