• Infection of the (upper) dermis and subcutaneous tissue
    • Superficial (involving just the upper tissues) is also known as Erysipelas (although it is often clinically very difficult to differentiate)
      • One way is that cellulitis tends to have poorly demarcated borders c.f. erysipelas

Aetiology/Risk factors

  • Risk factors include
    • Previous cellulitis
    • Venous disease e.g. venous eczema, venous ulcers; and/or lymphoedema
    • Current/prior injury e.g. trauma, surgery, radiotherapy
    • Diabetes, alcoholism, obesity
    • Pregnancy
    • Fungal infection (between toes)
    • Concomitant skin disease
  • Most cases are caused by beta-haemolytic streptococcus e.g. Streptococcus pyogenes (2/3 cases) or by Staph aureus
    • Rarer causes include Pseudomonas aeruginosa (puncture wounds); H Influenzae (children with facial cellulitis); Anaerobes (from human bites); Pasteurella multocida (cat/dog bites)


  • Classically acute onset red, painful, hot, swollen and tender skin.
    • Can spread rapidly
    • Almost always unilateral
    • There may be evidence of a break in the skin (or other source of infection)
  • Other symptoms include fever, malaise, nausea, shivering and rigors
    • The patient may also have evidence of sepsis e.g. tachycardia, tachypnoeia, confusion, hypotension etc


  • Usually a clinical diagnosis (start treatment before cultures/sensitivity)
    • In patients who present atypically, swabs/cultures from entry sites or broken/weeping skin may be useful
    • In patients where other causes e.g. DVT, might be possible, appropriate investigations should be performed e.g. D-Dimers, USS


  • Antibiotic treatment
    • If in the community- 1g Flucloxacillin four times daily for 7 days (Doxycycline in penicillin allergic or risk of MRSA)
    • If the patient is Septic, patients should be referred to hospital for IV Flucloxacillin 1g QDS (increase to 2g if BMI>30)
      • IVOST when appropriate
      • if penicillin allergic, IV vancomycin can be used
    • If the patient is in severe sepsis and/or has Necrotising Fasciitis
      • Refer to HDU and give IV Flucloxacillin (2g QDS) + Clindamycin (1.2g QDS) + Gentamycin (7mg/kg as per protocol)
      • Omit flucloxacillin if allergic and add vancomycin if suspected MRSA infection

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