Rapidly progressive, life-threatening deep soft tissue infection requiring emergent surgical debridement and broad-spectrum antibiotics.
Also known as: necrotizing fasciitis, nec fasc, Fournier gangrene, flesh-eating bacteria
Overview
Severe necrotizing soft tissue infection of the fascia and subcutaneous tissue with progressive thrombosis of vessels supplying the skin. Classified as Type I (polymicrobial — mixed aerobes/anaerobes), Type II (monomicrobial — group A streptococcus, occasionally Staphylococcus aureus), Type III (gram-negative including Vibrio vulnificus, marine exposure or chronic liver disease), Type IV (fungal — immunocompromised, often after trauma).
Epidemiology
Annual US incidence ~1,000-1,500 cases. Mortality 20-40% even with treatment, climbing sharply with delayed surgical intervention. Higher in diabetics, immunocompromised, IV drug users.
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Anesthesia of overlying skin as cutaneous nerves are destroyed (a late, ominous sign)
Signs / physical exam
Skin findings often deceptively mild early — dusky/purplish discoloration, bullae (especially hemorrhagic), crepitus, foul-smelling 'dishwater' discharge
Septic shock, hemodynamic instability
Fournier gangrene: perineal/genital involvement
Cervical/dental source possible (Ludwig angina, descending mediastinitis)
Classic findings
Patient with severe pain disproportionate to exam, rapidly spreading edema, hemorrhagic bullae, and systemic toxicity — emergency surgical exploration regardless of imaging.
Differential diagnosis
Cellulitis/erysipelas — Pain proportional to exam, sharper borders, no systemic toxicity, no bullae or crepitus
Pyomyositis — Deep muscle abscess, often Staphylococcus aureus; imaging localizes
Gas gangrene (clostridial myonecrosis) — Crepitus, brown 'dishwater' discharge, sweet odor; overlap with Type I nec fasc; treat similarly
DVT — Swelling and tenderness without progression of skin findings; duplex ultrasound
Blood cultures, wound cultures (deep tissue at surgery)
LRINEC score (CRP, WBC, Hgb, Na, Cr, glucose) — ≥6 suggests necrotizing infection; sensitivity imperfect, do not use to exclude
Creatine kinase (elevated with muscle involvement)
Imaging
Plain films may show soft tissue gas (not always present)
CT with contrast (most useful): fascial thickening, gas, fluid tracking along fascia, lack of fascial enhancement
MRI sensitive but rarely available emergently
Bedside ultrasound: subcutaneous gas, fluid
DO NOT delay surgical consultation for imaging in a deteriorating patient
Diagnostic algorithm
Type
Microbiology
Typical Setting
Antibiotic Add-on
I
Polymicrobial (mixed aerobes/anaerobes)
Diabetic foot, post-op, Fournier
Piperacillin-tazobactam or carbapenem
II
Monomicrobial — Group A strep ± S. aureus
Healthy young patient, varicella
Vancomycin + clindamycin
III
Vibrio vulnificus, Aeromonas
Cirrhosis + saltwater/oysters
Doxycycline + ceftriaxone/cipro
IV
Fungal (mucormycosis)
Immunocompromise, trauma
Amphotericin B + surgical debridement
Necrotizing fasciitis classification by microbiology with targeted empiric coverage.
Treatment
First-line
Emergent surgical debridement is the cornerstone — every hour of delay increases mortality (Wong 2003)
Broad-spectrum empiric antibiotics immediately:
• Vancomycin OR linezolid OR daptomycin (MRSA coverage; linezolid also blocks toxin production)
• PLUS piperacillin-tazobactam OR carbapenem (meropenem, imipenem) for gram-negative and anaerobic coverage
• PLUS clindamycin (anti-toxin effect against group A strep and clostridial superantigens; suppresses protein synthesis)
Aggressive fluid resuscitation and vasopressor support
Tetanus prophylaxis updated
Repeat surgical exploration at 24 hours to ensure adequate debridement; may require multiple operations
Second-line / adjunct
IV immunoglobulin (IVIG) — may be considered in streptococcal toxic shock syndrome (controversial, INSTINCT trial neutral but some observational benefit)
Hyperbaric oxygen — adjunctive in clostridial myonecrosis; availability limited; should not delay surgery
Wound vacuum and reconstructive surgery after infection control
Complications
Streptococcal or staphylococcal toxic shock syndrome
Multi-organ failure, ARDS, AKI requiring dialysis
Limb loss, perineal amputation (Fournier)
Heterotopic ossification, chronic pain
Death (20-40%)
PANCE pearls
Pain out of proportion in a patient with seemingly mild skin findings is the single most important early clue.
LRINEC ≥6 supports the diagnosis but a low score does NOT rule out necrotizing infection — clinical suspicion trumps the score.
Clindamycin is added for its antitoxin effect (blocks ribosomal protein synthesis) — keep it on even after streptococcal speciation.
Vibrio vulnificus necrotizing infection: think cirrhotic patient + raw oyster ingestion or saltwater wound; add doxycycline + ceftriaxone.
Surgical debridement saves lives more than any antibiotic — do not delay for imaging or stable hemodynamics.
References
IDSA 2014 — Stevens et al., Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections (Clin Infect Dis)
Wong 2003 — Wong et al., Necrotizing fasciitis: clinical presentation, microbiology, and determinants of mortality (JBJS)
LRINEC — Wong et al., The LRINEC score: a tool for distinguishing necrotizing fasciitis from other soft tissue infections (Crit Care Med 2004)
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