- 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
- 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
Pediatric Considerations
- 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