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Necrotising fasciitis is a serious bacterial infection of the soft tissue and fascia. The bacteria multiply and release toxins and enzymes that result in thrombosis (clotting) in the blood vessels and subsequent ischaemia. The result is destruction of the soft tissues and fascia.
The main types of necrotising fasciitis are:
- Type I (polymicrobial incl. Staphylococcus aureus, Haemophilus, Vibrio and several other aerobic and anaerobic strains (Escherichia coli, Bacteroides fragilis))
- Type II (due to haemolytic group A streptococcus, staphylococci including methicillin resistant
- Type III (gas gangrene, i.e. due to Clostridium perfringens)
- Other: Marine organisms (vibrio species, Aeromonas hydrophila, considered Type III in some reports) and fungal infections (candida and zygomycetes, type IV in some reports)
The most common site of infection is the lower leg. Symptoms usually appear within 24 hours of a minor injury/postsurgery. Pain is often very severe at presentation and worsens with time. There may be systemic features such as fever, malaise, nausea and vomiting. As necrotising fasciitis develops the affected area starts to swell and may develop a purplish rash. Large haemorrhagic blisters form. The soft tissue starts to necrose. Subcutaneous crepitus may be present. Severe pain continues until necrosis destroys peripheral nerves. By about day 4 – 5 the patient is shocked. Metastatic abscesses can develop in the liver, lung, spleen, brain, pericardium, and rarely, in the skin.
The diagnosis is a clinical one. Blood culture, deep tissue biopsy and Gram stain help in identifying the culprit organism(s) and guide the choice of antibiotic. Radiological imaging identifles areas of fluid collection, inflammation and gas within the soft tissues.
Treatment involves high-dose broad spectrum intravenous antibiotics and supportive management with fluid resuscitation. Patients require prompt surgery to debride the affected area. When the acute infection has subsided, the wound should be closed with skin grafting if required.
Necrotising fasciitis has a mortality of 25%. Prompt diagnosis and treatment is essential to reducing the risk of death and disgurement from necrotising fasciitis.