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Cellulitis

Medicine > Infection

Background knowledge 🧠

Definition

  • Cellulitis is a common bacterial infection of the deeper layers of the skin (dermis) and subcutaneous tissues.
  • Usually involves areas with disrupted skin, e.g. cuts, ulcers, or insect bites.
  • Most cases are caused by Streptococcus pyogenes and Staphylococcus aureus.

Epidemiology

  • Affects all age groups, but more common in older adults.
  • Incidence higher in individuals with chronic illnesses like diabetes and peripheral vascular disease.
  • More prevalent in lower extremities, particularly legs.

Aetiology and pathophysiology

  • Caused by bacterial invasion, typically through breaches in the skin barrier.
  • Group A Streptococcus and Staphylococcus aureus are the most common pathogens.
  • Inflammatory response leads to erythema, warmth, pain, and swelling.
  • Risk factors: trauma, obesity, oedema, immunocompromise.

Types

  • Non-purulent: Streptococcus predominant, presents with diffuse erythema.
  • Purulent: Staphylococcus aureus, typically with abscess formation.
  • Recurrent: Often seen in patients with chronic oedema or venous insufficiency.
  • Necrotising: Rapidly progressing form, requires urgent intervention.

Clinical Features 🌡️

Symptoms

  • Fever, chills, and malaise.
  • Localised pain and tenderness over the affected area.
  • Skin redness and warmth.
  • Rapid spread of erythema over hours to days.
  • Swelling of the skin and subcutaneous tissues.

Signs

  • Erythema with poorly defined margins.
  • Warm, tender, and swollen skin.
  • Lymphangitis (red streaking).
  • Regional lymphadenopathy.
  • May have blistering or purulent discharge.

Investigations 🧪

Tests

  • Clinical diagnosis based on presentation.
  • FBC: May show leukocytosis.
  • CRP and ESR: Elevated in inflammation.
  • Blood cultures if systemic symptoms present.
  • Wound swabs in purulent cases to identify pathogen.

Management 🥼

Management

  • Antibiotics: Flucloxacillin (first-line), alternatives include clindamycin or co-amoxiclav.
  • IV antibiotics for severe or systemic cases.
  • Elevation of the affected limb to reduce swelling.
  • Analgesia for pain control.
  • Consider surgical debridement if necrosis is present.

Complications

  • Abscess formation.
  • Sepsis and septic shock.
  • Necrotising fasciitis.
  • Recurrent cellulitis.
  • Lymphoedema from chronic inflammation.

Prognosis

  • Good with timely treatment in uncomplicated cases.
  • Severe cases can lead to hospitalisation or complications.
  • Risk of recurrence in individuals with predisposing factors.

Key points

  • Recognise cellulitis early to prevent complications.
  • Antibiotic therapy is the cornerstone of management.
  • Consider risk factors for recurrence and address them where possible.
  • Urgent referral for necrotising fasciitis or signs of systemic infection.

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Infection