Necrotising soft-tissue infection

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Necrotising soft-tissue infection includes necrotising fasciitis, myonecrosis and rapidly destructive infection of fascia, subcutaneous tissue or muscle. It may be polymicrobial or caused by a single virulent organism such as group A Streptococcus.

The decisive diagnostic test is operative inspection of fascia and tissue viability. Clinical suspicion should trigger surgery because laboratory scores and cross-sectional imaging can be falsely reassuring in early disease.

Antibiotics reduce bloodstream and advancing microbial burden but cannot penetrate thrombosed, devitalised tissue adequately. Wide excision back to healthy bleeding tissue is therefore causal treatment.

Management continues after the first operation: serial examination and re-exploration, intensive care, renal and coagulation support, glycaemic control, nutrition, wound reconstruction and rehabilitation are frequently required.

Key points

Necrotising soft-tissue infection spreads along fascia, thromboses small vessels and destroys tissue faster than antibiotics can achieve source control.
Early skin may look modest; severe escalating pain, oedema beyond erythema and systemic toxicity carry more weight than colour.
Do not use a low LRINEC score, normal radiograph or absent gas to rule out disease.
First management priority is immediate surgical exploration and excisional debridement; imaging is reserved for uncertainty in a stable patient when it will not delay theatre.
Start broad intravenous antibacterial therapy immediately after useful cultures, covering streptococci, staphylococci, Gram-negative organisms and anaerobes according to local policy.
Add high-dose clindamycin for suspected streptococcal or clostridial toxin suppression even if laboratory susceptibility to a beta-lactam is expected.
Confirmed group A streptococcal disease can be narrowed with microbiology to benzylpenicillin 2.4 g intravenously every four hours plus clindamycin 1.2 g every six hours.
Expect serial operations, intensive organ support, nutritional rehabilitation and reconstructive planning rather than a single debridement and short antibiotic course.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Polymicrobial infection

Mixed aerobic and anaerobic organisms cause many infections after surgery, perineal disease, diabetes or chronic wounds, particularly in immunocompromised hosts.

Monomicrobial invasive pathogens

Group A Streptococcus, Staphylococcus aureus and clostridia can cause fulminant disease after minor trauma or with no obvious portal.

Water-associated organisms

Vibrio vulnificus after seawater exposure and Aeromonas after freshwater injury can produce rapidly destructive infection, especially with liver disease or immune compromise.

Anatomical portals

Penetrating injury, injection, childbirth, operation, pressure injury, perianal disease and mucosal breach introduce organisms into deep tissue planes.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Fascial-plane spread
Organisms and enzymes track rapidly along relatively avascular fascia, allowing extensive deep progression before overlying skin changes become dramatic.
2
Microvascular thrombosis
Inflammation, platelet activation and bacterial toxins thrombose small vessels, causing ischaemia, antibiotic-delivery failure and expanding tissue necrosis.
3
Exotoxin amplification
Streptococcal and staphylococcal superantigens activate large T-cell populations, producing cytokine release, vasoplegia, capillary leak and multiorgan shock.
4
Compartment and muscle injury
Oedema within confined fascial spaces impairs perfusion further, while myonecrosis releases potassium, acid and creatine kinase into the circulation.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Disproportionate escalating painRed flag

Deep severe pain beyond the visible erythematous margin, particularly when rapidly worsening, is an important early feature before skin necrosis develops.

Rapid oedematous spreadRed flag

Tense swelling extending beyond erythema, woody induration and progression over hours suggest fascial-plane spread rather than routine cellulitis.

Late cutaneous signsRed flag

Dusky discoloration, haemorrhagic bullae, skin anaesthesia, necrosis and crepitus indicate microvascular failure and advanced destructive disease.

Toxin-mediated systemic illnessRed flag

Rigors, vomiting, diarrhoea, confusion, hypotension, coagulopathy and multiorgan dysfunction may dominate the presentation, especially with streptococcal infection.

High-risk portalRed flag

Recent surgery, perineal infection, childbirth, injection, penetrating injury, chronic ulcer or seawater and freshwater exposure provides an organism and anatomy clue.

Apparently normal early skinRed flag

Severe pain and physiological decline with limited surface change should increase rather than reduce concern because fascial disease begins deep.

Red flags requiring action

Pain out of proportion to visible skin change is an early necrotising-infection warning.
Rapid progression over hours despite antibiotics requires immediate senior surgical reassessment.
Haemorrhagic bullae, dusky skin, anaesthesia or necrosis indicates advanced tissue and nerve injury.
Crepitus or gas on imaging supports gas-forming infection but its absence does not reassure.
Hypotension, confusion, coagulopathy, lactate rise or acute kidney injury signals toxin-mediated shock.
Recent surgery, penetrating trauma, childbirth, injection, immune compromise or water exposure changes organism risk.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Immediate senior surgical assessmentFirst step
Why
Determine whether clinical suspicion warrants operative exploration without diagnostic delay.
Interpretation and limitations
A sufficiently concerning syndrome is an indication for theatre. Do not demand a score, scan or visible necrosis before involving the operating team.
02
Operative fascial and muscle inspection
Why
Confirm tissue-plane necrosis and define the extent of excision required.
Interpretation and limitations
Grey fascia, thin turbid fluid, loss of resistance to blunt dissection, non-contractile muscle and absent bleeding support necrosis; send multiple deep samples.
03
Blood cultures and deep tissue microbiology
Why
Identify bloodstream and invasive organisms for later antimicrobial narrowing.
Interpretation and limitations
Take blood cultures before therapy when this causes no delay; deep operative tissue and fluid are more representative than superficial wound swabs.
04
Full blood count, CRP, renal, liver, coagulation and creatine kinase
Why
Assess inflammatory burden, muscle injury, organ failure and operative risk.
Interpretation and limitations
Abnormal sodium, creatinine, platelets, INR or CK supports severity but no normal laboratory pattern safely excludes early necrotising infection.
05
Blood gas, lactate and glucose
Why
Measure hypoperfusion, metabolic disturbance and diabetic decompensation during resuscitation.
Interpretation and limitations
Trend lactate with perfusion and response; a normal initial lactate does not override a rapidly progressive local and systemic syndrome.
06
Contrast CT or MRI in selected stability
Why
Map gas, deep fluid and alternative pathology when diagnosis or extent remains uncertain.
Interpretation and limitations
Imaging can support planning but lacks perfect sensitivity and must never postpone exploration in an unstable or clinically convincing presentation.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Severe cellulitis

Superficial warmth and tenderness without disproportionate pain, fascial progression, anaesthesia or shock is more compatible with uncomplicated skin infection.

Pyomyositis or deep abscess

Focal muscle pain and collection may cause sepsis but usually requires targeted drainage rather than wide fascial excision.

Acute limb ischaemia

Pain, pallor, pulselessness, coolness and neurological deficit requires immediate vascular assessment and can coexist with infected tissue.

Compartment syndrome

Tense compartments, pain on passive stretch and neurological change after injury demands emergency fasciotomy even without primary infection.

Inflammatory necrotic dermatosis

Pyoderma gangrenosum, vasculitis and calciphylaxis can ulcerate and worsen after trauma, requiring dermatology and histological assessment once infection is addressed.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01SUSPECTActivate surgery and resuscitationFirst stepDisproportionate pain, rapid progression, fascial signs or systemic toxicity creates meaningful suspicion.

1Use ABCDE, obtain large-bore access, measure lactate and glucose, send blood cultures and organ-function tests and begin physiology-guided crystalloid resuscitation.
2Contact senior surgery, anaesthesia, critical care and microbiology simultaneously and communicate why operative exploration cannot wait for diagnostic certainty.
3Start broad intravenous antibacterial therapy plus toxin-suppressing clindamycin according to the local necrotising-infection pathway after cultures when feasible.
4Provide strong analgesia, keep the patient fasted, correct major coagulopathy when possible and transfer to theatre without waiting for imaging or a LRINEC score.

02OPERATEExcise all non-viable tissueClinical suspicion remains high or operative exploration confirms fascial or muscle necrosis.

1Open involved compartments widely, release fascial planes and excise skin, subcutaneous tissue, fascia and muscle until viable bleeding tissue remains.
2Send multiple separate deep tissue and fluid samples for microscopy, aerobic and anaerobic culture and histology, adding fungal testing when exposure or host factors support it.
3Plan scheduled re-exploration within the surgical timeframe and return sooner for continuing shock, pain or advancing skin change.
4Coordinate blood-product support, renal replacement, ventilation, vasopressors, nutrition and wound management through critical care.

03DIRECTNarrow after source controlOperative findings and microbiology define the organism while the patient stabilises.

1Review blood and deep-tissue results daily with microbiology and remove unnecessary empirical components while maintaining reliable invasive-site exposure.
2AlternativeFor confirmed group A streptococcal infection, use benzylpenicillin plus clindamycin at high intravenous doses unless allergy or susceptibility requires an alternative.
3Base total duration on serial source control, viable tissue, bacteraemia and systemic recovery rather than a fixed cellulitis course.
4Discuss intravenous immunoglobulin only for selected severe streptococcal toxic shock through critical care and infection specialists because evidence and supply require case-specific judgment.

04RECOVERReconstruct and prevent recurrenceAll necrotic tissue has been controlled and physiology is improving after serial operations.

1Use multidisciplinary wound, plastics, stoma, urology or orthopaedic expertise according to anatomy and plan closure, grafting or reconstruction after infection control.
2Provide high-protein nutrition, glycaemic management, analgesia, thromboprophylaxis and early physical and psychological rehabilitation.
3Address diabetes, pressure injury, injecting practice, chronic wounds, perineal disease or occupational water exposure that contributed to entry.
4Document antimicrobial stop criteria, wound surveillance, functional goals and symptoms requiring urgent re-examination after discharge.

Key medicines and prescribing safety4 treatments · regimens, roles and cautions

Provides immediate broad Gram-positive, resistant staphylococcal, Gram-negative and anaerobic coverage with toxin suppression before cultures define the infection.

Empirical piperacillin–tazobactam, clindamycin and vancomycin

Where the local severe soft-tissue pathway selects it, give piperacillin–tazobactam 4.5 g intravenously every six hours plus clindamycin 1.2 g every six hours and weight- and level-guided intravenous vancomycin.

This combination is locally dependent; clarify beta-lactam allergy, calculate renal function and dosing weight, monitor vancomycin levels and kidney injury, and adjust promptly using deep cultures.

Combines rapid streptococcal killing with protein-synthesis inhibition to reduce ongoing exotoxin production.

Benzylpenicillin plus clindamycin for confirmed GAS

Give benzylpenicillin 2.4 g intravenously every four hours plus clindamycin 1.2 g intravenously every six hours after microbiology confirms susceptible group A Streptococcus.

Check immediate penicillin allergy, renal and hepatic function and clindamycin-associated diarrhoea; continue surgical source control because antimicrobial activity cannot rescue necrotic tissue.

Suppresses bacterial protein and toxin synthesis and retains activity in high-inoculum stationary-phase infection.

Clindamycin toxin-suppression component

Give 1.2 g intravenously every six hours in severe suspected streptococcal or clostridial necrotising infection alongside definitive bactericidal therapy.

Never use alone for broad empirical cover; review liver function, gastrointestinal intolerance and Clostridioides difficile risk and stop when toxin-suppression benefit no longer outweighs harm.

Adds activity against methicillin-resistant staphylococci where healthcare exposure, colonisation or local epidemiology makes this necessary.

Vancomycin empirical component

Use the current local intravenous loading and maintenance protocol based on actual body weight, renal function, infection severity and measured serum exposure.

Obtain baseline renal function, record dosing weight and infusion plan, monitor concentrations and kidney injury and remove promptly when cultures exclude resistant Gram-positive infection.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Refractory septic shock

Exotoxin release, vasoplegia, myocardial depression and capillary leak cause persistent hypotension and multiorgan failure despite fluid and vasopressors.

Limb or organ loss

Extensive devitalisation may require amputation, orchiectomy, bowel diversion or radical resection to achieve survival and source control.

Acute kidney injury

Shock, rhabdomyolysis, nephrotoxic exposure and massive inflammatory burden can cause severe acute kidney injury requiring temporary or prolonged renal replacement therapy.

Coagulopathy and bleeding

Disseminated intravascular coagulation, thrombocytopenia and repeated major surgery substantially increase haemorrhage, anaesthetic risk and blood-product transfusion requirements.

Long-term functional trauma

Large wounds, amputation, chronic pain, altered body image and critical-illness weakness create prolonged physical and psychological rehabilitation needs.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Use continuous or very frequent observations, arterial pressure, lactate, urine output and peripheral perfusion monitoring during shock.
Repeat full skin and limb examination after every resuscitation or operation and mark newly concerning margins without concealing the operative field.
Track renal, hepatic, coagulation, platelet, CK, acid-base and glucose trends because multiorgan failure may evolve rapidly.
Review blood and each deep-tissue culture daily and document antimicrobial indication, dose, allergy, levels and narrowing decisions.
Assess the need for repeat debridement from physiology and wound viability rather than waiting for inflammatory markers to peak.
During recovery monitor nutritional delivery, wound progress, graft viability, pain, mobility, limb function and psychological trauma.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Operative diagnosis outranks LRINEC

Laboratory-risk scores were not designed to rule out early disease and can create fatal reassurance when clinical progression is convincing.

Anaesthesia can follow pain

Intense early pain may later lessen as cutaneous nerves infarct; apparent pain improvement with dusky skin can indicate worsening necrosis.

Gas is neither required nor specific

Many streptococcal cases contain no visible gas, while gas can occur in other infections and after procedures.

Clindamycin is an adjunct

Toxin suppression complements broad and bactericidal therapy but never replaces immediate radical excision of devitalised tissue.

One operation is often insufficient

Microscopic progression beyond apparently viable margins makes planned serial inspection and further debridement a normal part of definitive care.

Exposure refines organisms

Seawater injury suggests Vibrio and freshwater exposure suggests Aeromonas, requiring urgent microbiology advice and exposure-specific empirical modification.

11Common pitfallsFrequent interpretation and management errors.

01
Do not wait for bullae, crepitus or necrosis before involving surgeons because these are often late findings.
02
Do not use a low LRINEC score or absent radiological gas to discharge a patient with progressive disproportionate pain.
03
Do not let CT or MRI delay theatre when the clinical syndrome already justifies exploration.
04
Do not rely on antibiotics without wide excision and planned re-examination of all devitalised tissue.
05
Do not treat a superficial swab as definitive when multiple deep operative samples are available.
06
Do not forget weight, renal function, serum-level monitoring and interaction review during high-dose multi-drug treatment.