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Cellulitis and Soft Tissue Infections

• Definitions:
  • Cellulitis is an infection of the skin and soft tissues, most commonly caused by Group A Streptococci and/or Staphylococcus aureus.
  • Erysipelas is a form of cellulitis with rapid onset, clearly demarcated margins and is almost exclusively caused by Group A Streptococci.
• Predisposing Factors:
  • Cellulitis/erysipelas may follow minor, sub-clinical skin trauma, or may arise in an area where there is dermatophyte infection, eczema, psoriasis, a traumatic or surgical wound or other break in the skin barrier.
  • Patients with venous insufficiency, oedema, lymphatic obstruction, previous cellulitis/erysipelas, diabetes, alcoholism or cerebrovascular disease have a high incidence of cellulitis and are prone to relapse.
• Investigations:
  • Blood cultures required only if patient is very unwell (i.e., satisfies criteria for SIRS), has lymphatic obstruction, or is immunocompromised.
  • Aspirate any skin blisters or fluctuant areas and swab any skin lesions, ulcers or wounds in the area of the infection.
  • CBC + diff, glucose, creatinine. Check immunoglobulins in patients with recurrent cellulitis.
  • In patients who are immunocompromised or who are not responding to standard treatment, consider subcutaneous aspirate or skin biopsy.
• Antibiotics:
  • Uncomplicated cellulitis of uncertain aetiology:
    • Use flucloxacillin 1-2 g IV q6h, until defervescence of fever, patient improved symptomatically or improved appearance of cellulitis, followed by flucloxacillin 0.5-1 g QID orally for 7-10 days.

      Note: Additional treatment with penicillin is not required.

    • If mild penicillin allergy (e.g., rash) then use cephazolin 1 g IV q8h.
    • If significant penicillin allergy (e.g., anaphylaxis, angioedema) then use clarithromycin IV with early switch to roxithromycin, or clindamycin.

      Note: Cellulitis commonly appears to worsen in the first 72 hours but this should not automatically lead to a change in antibiotics unless the patient's overall condition (e.g., fever, pulse, BP) deteriorates. Typically over this time the patient improves symptomatically and starts to defervesce. Community acquired MRSA infections are increasingly recognized. Consider these in all patients with cellulitis which is not responding to beta-lactam antibiotics.

  • Complicated cellulitis:
    • Cellulitis associated with burns, chronic venous or decubitus ulcers, wounds, or in patients with diabetes, vascular insufficiency or immunocompromise. These infections are often polymicrobial; predominantly Group A Streptococci and Staphylococcus aureus but Gram negative enteric bacilli and anaerobes may also be present.
    • Consider underlying osteomyelitis in those with diabetes, vascular insufficiency, or chronic ankle or decubitus ulcers.
    • Remember anti-tetanus prophylaxis for traumatic wounds.
    • While awaiting results of appropriate swabs, aspirates or surgical debridement, the following antibiotic combinations are recommended:
      Amoxicillin/ clavulanate 1.2 g IV q8h with or without gentamicin or cefuroxime + metronidazole or flucloxacillin + gentamicin + metronidazole.
  • Erysipelas and cellulitis thought to be caused by Group A Streptococci can be treated by penicillin alone. Give benzylpenicillin 1.2g q4h IV.
  • Necrotizing skin and soft tissue infections:
    • Early on these are very difficult to distinguish from cellulitis / soft tissue infections and diagnosis is frequently delayed leading to high morbidity and mortality. Changes of skin necrosis and anaesthesia are late signs and require urgent management.
    • Suggestive clinical features include severe / disproportionate pain, tenderness beyond visible erythema, bullae formation, haemorrhagic bullae, necrosis and anaesthesia.
    • The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score can help distinguish necrotizing fasciitis from other soft tissue infections.

Crit Care Med 2004;32:1535

• A score of ≥6 should raise suspicion of necrotizing fasciitis and a score of ≥8 is strongly predictive of the disease.
• Rescoring of patients during admission who aren’t responding to treatment is also useful.
• Management: IV flucloxacillin 2 g q4h-q6h + IV clindamycin 600 mg q6h + IV gentamicin. If penicillin allergy, give IV ceftriaxone 2 g q12h + clindamycin.
• Early and aggressive debridement of involved tissue is essential. Urgent surgical referral.
• Tissue specimens sent to the Microbiology Laboratory for Gram stain and culture.
• Consult Infectious Diseases urgently. Notify Microbiology Laboratory of incoming specimen.

Topic Code: 2732