Illustration: a translucent lower leg with smooth, calm skin, while a copper glow with tiny gas bubbles spreads along the deep layers around the calf muscles.
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EMA Cited · Infectious disease · Surgical emergency

Necrotizing soft tissue infection

Updated Oct 28, 2026Adults · ED management12 sources · 10 in PubMed2 figuresWSES 2022 · IDSA 2014

Bottom line

  • Suspect it early. Most cases are first diagnosed as cellulitis. Swelling, redness and pain out of proportion to the exam should raise the alarm.1
  • Call the surgeon on suspicion, not proof. Surgery within 6 hours of arrival was linked to 19% mortality, against 32% when it came later (OR 0.43).2
  • No single finding rules it out. Fever was present in only 46% and hypotension in 21%. A LRINEC score ≥ 6 missed about a third of cases (sensitivity 68%).3
  • Imaging must not delay the operating room. CT is the best ED test (sensitivity 89%, specificity 93%). Plain films miss about half of cases.3,1
  • Antibiotics: broad, plus a toxin blocker. Cover MRSA, Gram-negatives and anaerobes, and include clindamycin or linezolid.1,4

Recognize

  • Common local signs: swelling (81% of cases), pain or tenderness (79%), erythema (71%), warmth (44%), bullae (26%), skin necrosis (24%) and crepitus (20%).1
  • Late signs: hemorrhagic bullae, crepitus, skin necrosis, dusky discoloration, wood-hard tissue and numb skin. Deep tissue is involved first, so the skin can look deceptively mild.5
  • Red flags: pain or swelling beyond the edge of the redness, systemic illness, and rapid spread.5 Treat a rapidly progressing soft tissue infection as necrotizing from the start. It can worsen within hours.1
  • Risk factors: diabetes (up to 44.5% of patients), kidney disease, arterial disease, injection drug use, BMI > 30, liver disease, immunosuppression, recent surgery, and skin breaks as minor as insect bites or injection sites.1
  • Ask about water. Seawater suggests Vibrio vulnificus, especially with liver disease. Fresh or brackish water, soil or wood suggests Aeromonas.1
TypeOrganismsTypical setting
I · polymicrobialAerobes and anaerobesBowel surgery, perineal or perianal abscess, pressure ulcers, injection sites1
II · monomicrobialGroup A strep, S. aureus; Vibrio, AeromonasCommunity-acquired, mostly limbs; about two-thirds in the legs1
III · gas gangreneClostridium (mostly C. perfringens)Trauma, or spontaneous; spreads within hours1

Fournier gangrene is an NSTI of the genitals or perineum, usually from an anorectal, urinary or skin source.1 The approach to diagnosis, antibiotics and surgery is similar for every type.1

First hour

  1. Call the surgeon now for suspected NSTI, systemic toxicity or suspected gas gangrene.4,1
  2. Resuscitate as for sepsis. Give 1 L of balanced crystalloid over 30 minutes, and up to 30 mL/kg within 3 hours if hypotensive or lactate is high. Start norepinephrine for a MAP under 65, peripherally if needed.1
  3. Give antibiotics within 1 hour. Use a broad regimen that includes clindamycin or linezolid (table below).1,4
  4. Draw blood cultures. Deep tissue samples taken during the first debridement identify the cause in most cases.1
  5. Image only if it won't delay surgery.1
FIG 1 · Decision flowCited
  1. Skin infection with red flags: pain out of proportion, pain or swelling beyond the redness, bullae, crepitus, systemic toxicity, or rapid spread.1,5
  2. Call the surgeon now, while you resuscitate.4,1
  3. Antibiotics within 1 hour: an anti-MRSA drug, piperacillin-tazobactam or a carbapenem, and clindamycin or linezolid. After seawater or fresh-water exposure, add doxycycline.1,4
  4. Resuscitate: 1 L balanced crystalloid over 30 min, up to 30 mL/kg within 3 h if hypotensive or lactate is high, norepinephrine for MAP < 65.1
  5. High clinical suspicion?
    Yes
    To the operating room, ideally within 6 hours of arrival. Don't wait for imaging or a score.2,1,6
  6. Uncertain
    CT if it won't delay surgery, or bedside ultrasound. A low LRINEC score or a normal X-ray does not rule it out.3,1,7
  7. Gas or fluid along the fascia, non-enhancing fascia, or still worried?
    Yes
    Surgical exploration. It is the definitive test.8,1
  8. No
    Admit and re-examine often. The picture can change within hours. Call the surgeon back if it spreads.1
  9. After surgery: ICU care, a re-look every 12–24 h, and antibiotics narrowed to the cultures.1
FIG 1Suspected necrotizing infection. Drawn for this page from the WSES 2022 pathways, the IDSA 2014 guideline and the studies cited below. Each box carries its own citations.1,4

Tests and scores

Finding or testSensitivitySpecificity
Examination
Fever46.0%77.0%
Hemorrhagic bullae25.2%95.8%
Hypotension21.0%97.7%
Imaging
Plain radiograph48.9%94.0%
CT88.5%93.3%
Score
LRINEC ≥ 668.2%84.8%
LRINEC ≥ 840.8%94.9%

Pooled from 23 studies (n = 5,982) in adults with a soft tissue infection worrying for NSTI, confirmed at surgery or by histology.3

LRINEC score

Lab0 pointsPoints
C-reactive protein< 150 mg/L≥ 150: 4
White cells (×1,000/µL)< 1515–25: 1 · > 25: 2
Hemoglobin (g/dL)> 13.511–13.5: 1 · < 11: 2
Sodium (mEq/L)≥ 135< 135: 2
Creatinine (mg/dL)≤ 1.6> 1.6: 2
Glucose (mg/dL)≤ 180> 180: 1

Items from MDCalc.6 The derivation study used a cutoff of 6.9

Sources disagree

In its retrospective derivation, a score of 6 or more had a negative predictive value of 96%.9 Pooled across later studies, LRINEC ≥ 6 had a sensitivity of only 68%.3 The WSES pathways call its accuracy poor, and say a low score does not rule out NSTI.1 MDCalc advises skipping the score when clinical suspicion is high and going straight to surgery.6

Imaging

  • CT: look for fat stranding, fluid and gas tracking along fascial planes, and fascia that is thickened or does not enhance with contrast.1
  • Plain X-ray should not be used to rule out NSTI.1
  • MRI is hard to do in an emergency and is not the first-choice test.1
  • Bedside ultrasound: in a review of 3 studies (n = 221), sensitivity ranged from 85.4% to 100% and specificity from 44.7% to 98.2%. Fluid along the fascia was the most sensitive sign (85.4%), and subcutaneous gas the most specific (100%).7
  • When suspicion is high, imaging must not delay or deter surgery.1
Axial CT of the upper abdomen showing dark pockets of gas dissecting through the soft tissues of the right flank and abdominal wall
FIG 2Gas in the soft tissues on CT. Black pockets of gas track through the soft tissues of the right flank and abdominal wall, outside the bowel.James Heilman, MD · Wikimedia Commons · CC BY-SA 4.0

At the bedside or in the OR

The finger test is done under local anesthetic through a 2 cm incision down to the deep fascia. Easy finger dissection, no bleeding, necrotic tissue or gray "dishwater" fluid all suggest NSTI.1 Surgical exploration remains the gold standard for diagnosis.8

Antibiotics

AgentAdult dose (normal renal function)Notes
Gram-negative and anaerobic cover (one of)
Piperacillin-tazobactam4.5 g IV every 6 hWSES dose for unstable patients. IDSA lists 3.37 g every 6–8 h.1,4
Meropenem1 g IV every 8 hPreferred where ESBL-producing organisms are common.1,4
Ceftriaxone + metronidazole2 g IV daily + 500 mg IV every 8 hWSES option for stable patients.1
MRSA cover (one of)
Vancomycin30 mg/kg/day IV in 2 divided dosesWSES gives a 25–30 mg/kg load. Adjust to levels and kidney function.4,1
Linezolid600 mg IV every 12 hAlso blocks toxin production.1,4
Toxin suppression
Clindamycin600–900 mg IV every 8 hAdd it unless linezolid is the MRSA drug.1,4
Directed therapy
Group A strep: penicillin + clindamycin2–4 million units IV every 4–6 h + 600–900 mg IV every 8 hFor documented streptococcal NSTI.4
Vibrio: doxycycline + ceftriaxone or cefotaximeDoxycycline 100 mg IV every 12 hSeawater exposure.4,1
Aeromonas: doxycycline + ciprofloxacin or ceftriaxoneDoxycycline 100 mg IV every 12 hFresh water or soil exposure.4,1

Unreviewed doses. Verify against the current label and your institution's protocol before giving anything.

Continue antibiotics until no further debridement is needed, then narrow them to the culture results.1 Set doses by the patient and the drug, with pharmacy input.1

  • Why clindamycin or linezolid: both can markedly reduce exotoxin production by Gram-positive organisms.1 In 1,956 US inpatients with invasive streptococcal infection on a beta-lactam, adding clindamycin in group A infection was linked to lower in-hospital mortality (6.5% vs 11.0%, adjusted OR 0.44).10
  • IVIG: in the INSTINCT trial, 100 ICU patients with NSTI received 25 g of IVIG or placebo daily for 3 days. Physical function at 6 months did not differ.11
  • Hyperbaric oxygen: there are no randomized trials. Use it only if available on site, and never transfer for it or let it delay surgery or ICU care.1
Sources disagree

The WSES pathways list IVIG for streptococcal NSTI, noting variable results mainly in streptococcal toxic shock.1 The only randomized trial found no benefit.11 An ED review concludes that neither IVIG nor hyperbaric oxygen has been shown to improve outcomes.8

Surgery and disposition

  • Time matters. Across 109 studies (6,051 patients), 21.1% died. Surgery within 6 hours of arrival was linked to lower mortality (OR 0.43; 19% vs 32%), and so was surgery within 12 hours (OR 0.41).2
  • Delays before arrival did not change mortality, and no timing measure reduced amputations.2
  • Debride in the operating room and remove all necrotic tissue, which can mean amputation.1,12
  • Re-look every 12–24 hours, or sooner if the patient worsens, until little or no further debridement is needed.1
  • ICU: about half of patients develop septic shock.1 Care needs surgeons, intensivists and infectious disease specialists working together.12
  • Fournier gangrene: a Fournier's Gangrene Severity Index above 9 predicts death.1

Pitfalls

  • Calling it cellulitis and sending the patient home. Most NSTIs are first diagnosed that way.1
  • Using a low LRINEC score, no fever or a normal X-ray to rule it out.3,6
  • Waiting for CT or MRI when suspicion is already high.1
  • Leaving out the toxin blocker (clindamycin or linezolid).1,4
  • Missing the water history that points to Vibrio or Aeromonas.1
  • Being reassured by mild-looking skin. Deep tissue is involved first.5
  • Transferring a patient for hyperbaric oxygen.1

How strong is the evidence?

The IDSA rates its NSTI recommendations strong but based on low-quality evidence.4 The 6-hour surgery target comes from a meta-analysis of 33 studies with 2,123 patients, not from trials.2 LRINEC was derived retrospectively.9 Support for clindamycin is from a retrospective cohort.10 The only randomized trial of IVIG was negative.11 NSTIs are commonly missed.8

On-shift teaching

Questions to ask a learner at the bedside. Tap a question to see the answer. Every answer uses facts cited above.

Q1How sensitive are fever and hypotension for NSTI?
Poorly. Pooled sensitivity was 46% for fever and 21% for hypotension. Their absence does not rule it out.3
Q2The LRINEC score is 4, but the patient has pain far beyond the redness. What next?
Call the surgeon. LRINEC ≥ 6 picks up only about 68% of cases,3 and MDCalc advises skipping the score when suspicion is high.6
Q3How much does the time to surgery matter?
Surgery within 6 hours of arrival was linked to 19% mortality, against 32% when later (OR 0.43).2
Q4Why add clindamycin or linezolid to a broad regimen?
Both reduce exotoxin production by Gram-positive organisms.1 In invasive group A strep, adding clindamycin was linked to lower in-hospital mortality (adjusted OR 0.44).10
Q5A patient with cirrhosis has a fast-spreading leg infection after cleaning fish at the beach. What organism, and what antibiotics?
Vibrio vulnificus. Give doxycycline with ceftriaxone or cefotaxime,4 plus prompt debridement and ICU care.1
Q6What CT findings suggest NSTI, and how good is CT?
Fat stranding, fluid and gas along fascial planes, and fascia that doesn't enhance.1 Pooled sensitivity was 88.5% and specificity 93.3%.3

References

Evidence base

What this page is built on

12 sources, cited 106 times. Dots are sources, filled by how far each was read; stronger color means a larger share of the citations. Tap a tier to see its sources.

Read in full · 4Abstract read · 8Record only · 0Link checked · 0

Checked by the writer, not a physician. The dots show how each source was read, not that anyone has confirmed the claims.

How this page was made
  • Written from scratch. No source text was copied; facts are restated and cited.
  • The WSES 2022 pathways and the IDSA 2014 guideline were read in full; antibiotic doses come from their text and dose tables. The 2026 Global Alliance for Infections in Surgery position statement was not openly accessible, so only its abstract is used. Trial and study results were checked against their PubMed abstracts.
  • LITFL's pages refused automated access, so they are not cited. The LRINEC items were checked on MDCalc because the WSES table has typographical errors in its hemoglobin bands.
  • Figure 1 was drawn for this page from cited sources. Figure 2 is an openly licensed image from Wikimedia Commons, credited under it, and keeps its own license.
  • Adults only. Pediatric necrotizing infections were not reviewed for this page.
  • Not for clinical use.
Not for clinical use

AI-generated draft. Not reviewed by a physician. This page is for education only and may contain errors, including in doses. Do not use it to diagnose, treat or make decisions about any patient. Rely on your own clinical judgment, your institution's protocols and current drug labeling. Reading this page does not create a physician-patient relationship. Full terms