Author: Amy Armstrong / Editor: Colin Bell, Jason Kendall / Reviewer: Sandi Angus / Codes: DC5, DC6, DP2, RP6, RP7, SLO3 / Published: 14/04/2023

Necrotising fasciitis is a rare but life threatening bacterial soft tissue infection. It is associated with significant mortality of approximately 20-40%, even with appropriate treatment1-3, and morbidity from skin and soft tissue loss2.Current literature suggests that there are approximately 500 new cases of necrotising fasciitis occurring annually in the UK. However, as there is no ongoing surveillance programme, this is felt to be an underestimation2,4.

A high index of clinical suspicion, prompt administration of broad-spectrum antibiotics and emergency surgery to debride affected tissues, are key to improving survival. Otherwise, rapid progression to multiorgan failure can occur – leading to systemic toxicity, limb loss and death5. Mortality is directly proportional to delay in diagnosis and treatment6-8.

Learning Bite

Necrotising fasciitis is rare but associated with significant morbidity and mortality. It represents a time critical pathology where patient outcome is directly influenced by time to diagnosis and treatment. A high index of suspicion is required to make the diagnosis at the earliest opportunity.

  • Necrotising fasciitis is the term used to describe progressive, fulminant bacterial infection of the subcutaneous tissue, that spreads rapidly through the fascial planes and causes extensive tissue necrosis and destruction9.
  • It can affect any part of the body, but most commonly involves the extremities, perineum or trunk10.
  • It is classified into 4 types according to causative organism (see table below)3,4,9.
  • Types I and II cause most of the necrotising fasciitis seen in the UK, whilst types III and IV are the rarest; normally only occurring in those with specific exposures, e.g. contaminated water, extensive burns or immunocompromised patients.
Type % total cases Aetiology Causative Organisms Site of Infection
I 70-80% cases Synergistic polymicrobial infection often bowel flora derived Mixture of obligate and facultative anaerobes and aerobes e.g. Bacteroides or Peptostreptococcus with an Enterobacteriaceae or non-group A streptococcus Anywhere, but most commonly trunk/perianal region
II 20-30% cases Mono-microbial infection Usually group A -haemolytic streptococcus, alone or in combination with staphylococcus aureus. Typically affects limbs
III Rare Gram-negative monomicrobial infection Marine organisms such as Vibrio spp. and Aeromonas hydrophila – occur following seawater contamination of wounds or ingestion of raw seafood mortality very high Limbs, trunk or perineum
IV Rare Fungal infection Zygomycetes (after traumatic wounds or burns) or candidal infection (in immunocompromised patients) Limbs, trunk or perineum

Learning Bite

Type I and II necrotising fasciitis (NF) make up most cases of NF seen in the UK. Type I is polymicrobial infection with mixed aerobes and anaerobes, often affecting the trunk/perineum. By contrast, type 2 NF is caused mostly by group A haemolytic streptococci and tends to affect the limbs.

  • The overlying skin may often appear unaffected initially due to the deep nature of the infection. This is unlike cellulitis where the infection begins at the junction between the dermis and superficial fascia and so appears red at the skin surface. In necrotising fasciitis, the infection starts at the level of subcutaneous fat and deep fascia, presenting a diagnostic challenge, as the extent of the infection is not clear from the surface10.
  • Type 2 NF is particularly associated with an exotoxin-driven toxic shock syndrome. This results from massive T-cell proliferation and cytokine release, and produces the typical clinical picture of NF, with profound hypotension and rapidly progressive multiorgan dysfunction leading to significant mortality11.

It requires a high index of clinical suspicion due to the non-specific early signs and symptoms, and its rapidly progressive nature.

Consideration of any risk factors listed below may help to point towards the diagnosis:

Risk Factors3,12

    • Age >50
    • IV drug use
    • Malnutrition
    • Chronic renal or liver disease
    • Obesity
    • Diabetes
    • Immunosuppression (including steroid use)
    • Skin injury insect bites, trauma, surgical wounds
    • Malignancy
    • Peripheral vascular disease

Clinical Features2,3,5

Early Signs Local erythema or a tense, ‘shiny’ swollen areaPain out of proportion to clinical findings severe and constant


Malaise or flu-like symptoms

Late Signs Tense oedema – ‘woody’ feel to skinBullae

Dusky blue/purple discolouration

Crepitus/surgical emphysema

Systemic features such as hypotension/septic shock and other signs of multi organ dysfunction e.g. confusion, anuria etc.

Learning Bite

Necrotising fasciitis is difficult to diagnose early due to the non-specific nature of its early features. It is often misdiagnosed for cellulitis and requires a high index of suspicion to identify. Consider cover for necrotising fasciitis in those patients who are more unwell with cellulitis than you would ordinarily expect, those with pain out of proportion to their clinical findings and those failing to respond to treatment!

Necrotising fasciitis is a clinical diagnosis and as such the gold standard investigation is surgical exploration and tissue biopsy9.

During Surgery, a lack of resistance to blunt dissection of the normally adherent superficial fascia, accompanied by a lack of bleeding and the presence of foul-smelling ‘dishwater’ pus, confirm the diagnosis9.

(i) Laboratory Investigations

    • Appropriate initial ED investigations are as for all patients presenting with sepsis – FBC, U+Es, LFTs, coagulation screen, CRP, lactate, ABG/VBG and blood cultures.
    • Bloods may show leucocytosis, acidosis, altered coagulation profile, hypoalbuminaemia and abnormal renal function.10

(ii) Imaging

    • CT, US and MRI have all been used to image necrotising soft tissue infection, however no imaging modality is considered definitive and it is vital to ensure that if imaging is performed, it must not unduly delay surgical intervention.

(iii) Adjuncts – Laboratory Risk Indicator for Necrotising Fasciitis9

    • As an adjunct to clinical judgement, scoring systems such as the Laboratory Risk Indicator for Necrotising Fasciitis (LRINEC) have been developed to help differentiate necrotising fasciitis from other soft tissue infections.
    • The LRINEC was developed following retrospective review of 89 cases of NF compared with 225 cases of other soft tissue infection and those variables which were most statistically significant discriminators combined to give a score.
    • Scores of six or more should raise the suspicion of NF and a score of eight or more is strongly predictive of the disease.
Variable Value Score
CRP (mg/L) <150>150 04
WCC (mm3) <1515-25




Haemoglobin (g/dL) >13.511.5-13.5




Sodium (mmol/l) >135<135 02
Creatinine (micromol/l) <141>141 02
Glucose (mmol/l) <10>10 02

Learning Bite

Necrotising fasciitis is ultimately a clinical diagnosis – results of other investigations are supportive only. If you suspect necrotising fasciitis prompt treatment should be instituted without delay!

(i) General Principles of Management

    • Necrotising fasciitis is a life and limb threatening surgical emergency and, if suspected, merits immediate senior surgical input.
    • Broad spectrum IV antibiotics should also be administered immediately in accordance with local consultant microbiologist advice.
    • Initial resuscitation should be aggressive – with IV crystalloid, blood products and inotropes, as required, to achieve haemodynamic, haemostatic and electrolyte stability.
    • The mainstay of treatment for necrotising fasciitis however remains early and aggressive surgical debridement of necrotic tissue until healthy, viable (bleeding) tissue is reached5,6,9.

(ii) Initial Resuscitation Phase

    • Aim: to establish adequate tissue perfusion and oxygen delivery to prevent or arrest the development of multi-organ dysfunction
    • Involves large volumes of IV crystalloid due to septic vasoplegia and significant 3rdspace losses, usually with invasive blood pressure monitoring and central venous access to allow inotropic support if indicated.
    • Early critical care review should be sought in addition to surgical consultation due to the anticipated clinical course for these patients, who are at high risk of multiorgan failure and significant associated mortality3,4.

(iii) Antibiotic Therapy

    • Antibiotics are a vital adjunct to source control and may attenuate the progression of septic shock when given early (within 1 hour), as well as reducing mortality13.
    • Antibiotics should be high dose, broad spectrum and given IV – and should be chosen to cover all likely causative organisms (Streptococci, Staphylococci, gram negative rods and anaerobes)14.
    • Example regimes are detailed below – though please follow local guidelines and discuss urgently with a local consultant microbiologist for patient specific advice.
    • In particular for suspected Type 2 NF, consider early administration of Clindamycin. Its bacteriostatic mechanisms inhibit the production of Streptococcal superantigen, felt to play a major role in the septic shock seen in these patients11.
    • Antibiotic therapy should be rationalised and tailored as culture results become available.

(iv) Surgical Management

    • Early and extensive debridement is the mainstay of management – timing and adequacy of debridement have been shown repeatedly to be the main determinant of patients outcomes6.
    • The goal of surgical intervention is to remove all necrotic and non-viable tissue until healthy tissue is reached7,8. This may involve amputation of limbs to gain control of infection.
    • Tissue samples should be sent urgently from theatre to a waiting lab for gram staining and culture, to help guide further antibiotic treatment.
    • Wounds should be covered, and the patient returned to the operating theatre 24 hours after initial debridement for a reassessment. Serial episodes of debridement may be required over a period of days6-8.

(v) Post-Operative Phase

    • Patients should be cared for in intensive care, using a multispecialty and multidisciplinary approach. Multidisciplinary team involvement is especially important during the rehabilitation phase.
    • Extensive debridement may result in significant wounds requiring vacuum assisted wound devices, skin grafting and specialist reconstructive surgery. This should be considered only when the patient has been stabilised and the infection fully eradicated4.
  • Necrotising fasciitis is a rare but potentially life-threatening infection that requires a high index of suspicion – if you don’t consider it in your differential you won’t diagnose it!
  • Time to surgical intervention is critical – ensure the whole team involved in caring for the patient know this and make efforts to keep momentum towards this!
  • Ensure relevant senior clinicians are aware of the patient and the working diagnosis. As a minimum, this should include ED, surgery, anaesthetics, microbiology and intensivists.
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  2. Anaya DA, Dellinger EP. Necrotising soft-tissue infection: diagnosis and management. Clin Infect Dis 2007; 44:705-10 [Accessed: 05/11/18]
  3. Misiakos EP, Bagias G, Patapis P, Sotiropoulos D, Kanavidis P, Machairas A. Current concepts in the management of necrotising fasciitis. Front Surg 2014,1:36. [Accessed: 05/11/18]
  4. Hasham S, Matteucci P, Stanley PR et al. Necrotising Fasciitis. BMJ 2005; 330:830. [Accessed: 06/11/18]
  5. Hakkarainen TW, Kopari NM, Pham TN, Evans HL. Necrotizing soft tissue infections: review and current concepts in treatment, systems of care, and outcomes. Curr Probl Surg. 2014;51(8):344-62. [Accessed: 06/11/18]
  6. Bilton BD, Zibari GB, McMillan RW. Aggressive surgical management of necrotizing fasciitis serves to decrease mortality: a retrospective study. Am Surg1998; 64:397-400. [Accessed: 06/11/18]
  7. Elliott DC, Kufera JA, Myers RA. Necrotizing soft tissue infections. Risk factors for mortality and strategies for management. Ann Surg1996;224:672-83. [Accessed: 06/11/18]
  8. Majeski J, Majeski E. Necrotising fasciitis: improved survival with early recognition by tissue biopsy and aggressive surgical treatment. South Med J1997;90:1065-8. [Accessed :6/11/18]
  9. Davoudian, P, Flint J. Necrotising Fasciitis. CEACCP 2012; 12(5): 245-250. [Accessed 07/11/18]
  10. Tidy C. Necrotising Fasciitis. Patient Plus article. Published July 2015. [Accessed: 12/11/18]
  11. Morgan MS. Diagnosis and management of necrotizing fasciitis: a multiparametric approach. J Hosp Inf 2010; 75: 249-257. [Accessed: 12/11/18].
  12. Sultan H, Boyle A, Sheppard, N. Necrotising fasciitis. BMJ 2012; 345: 42-74. [Accessed: 14/11/18]
  13. Kumar A, Roberts D, Wood KE, Light B, Parillo JE, Sharma S et al. Duration of hypotension before initiation of effective antimicrobial therapy is the critical determinant of survival in human septic shock. Crit Care Med 2006. 34(6);1589 1596. [Accessed: 18/11/18]
  14. Kwak YG, Choi SH, Kim T, et al. Clinical Guidelines for the Antibiotic Treatment for Community-Acquired Skin and Soft Tissue Infection. Infect Chemother. 2017;49(4):301-325. [Accessed: 20/11/18]