Cellulitis & Erysipelas Summary

Definitions

  • Cellulitis: Acute bacterial infection of dermis and subcutaneous tissue
  • Erysipelas: Superficial cellulitis with sharply demarcated borders
  • Common pathogens: Streptococcus pyogenes, Staphylococcus aureus

Risk Factors

  • Skin breaks (trauma, ulcers, fungal infections)
  • Lymphoedema, venous insufficiency
  • Obesity, pregnancy
  • Diabetes, immunocompromise, alcohol misuse

Clinical Features

  • Acute red, painful, hot, swollen skin
  • Fever, malaise, rigors
  • Rapid spread, blisters/bullae
  • Lymphangitis, peau d'orange appearance

Eron Classification

  • Class I: No systemic toxicity
  • Class II: Systemic unwell or complicating comorbidity
  • Class III: Significant systemic upset
  • Class IV: Sepsis or life-threatening infection

Management

  • Admit if: Class II-IV, severe disease, immunocompromised, facial cellulitis
  • IV antibiotics: Flucloxacillin first-line
  • Outpatient: Class I with oral flucloxacillin
  • Mark extent, elevate limb, manage skin breaks

Complications

  • Acute: Necrotising fasciitis, sepsis, abscesses
  • Chronic: Ulceration, lymphoedema, recurrence

Cellulitis and Erysipelas

Bacterial skin infections of the dermis and subcutaneous tissue

Introduction

Cellulitis is an acute bacterial infection of the dermis and subcutaneous tissue. The infected area is characterised by pain, warmth, swelling, and erythema. Blisters and bullae may form. Fever, malaise, nausea, and rigors may accompany or precede the skin changes.

Cellulitis most commonly affects the lower limbs, but other areas, such as the upper limbs, face, ears, and trunk, can also be affected. The most common causative organisms are Streptococcus pyogenes or Staphylococcus aureus.

Risk Factors

Most cases of cellulitis arise from bacterial infection through a break in the skin, for example from trauma (due to a bite, burn, or laceration), leg ulceration, maceration or fungal infection between the toes, or a concomitant skin disorder (such as atopic eczema).

General Risk Factors

  • Lymphoedema
  • Leg oedema
  • Venous insufficiency and history of venous surgery
  • Obesity
  • Pregnancy

Risk Factors for Severe Disease

  • Diabetes mellitus
  • Chronic liver or renal disease
  • Immunocompromise and neutropenia
  • Chickenpox (varicella)
  • Alcohol misuse
  • Neuropathy

Clinical Features

Cellulitis is more commonly seen in the lower limbs and usually affects one limb (bilateral leg cellulitis is very rare). Typical features include:

Local Signs

  • Acute onset of red, painful, hot, swollen, tender skin
  • Rapid spread of infection
  • Obvious skin break (wound, macerated skin, fungal infection)
  • Diffuse redness or well-demarcated edge
  • Blisters and bullae
  • Peau d'orange appearance with significant swelling
  • Inflamed regional lymph nodes or lymphangitis

Systemic Symptoms

  • Fever, malaise
  • Nausea, shivering
  • Rigors
  • May precede skin changes

Eron Classification System

Class I

  • No signs of systemic toxicity
  • No uncontrolled comorbidities

Class II

  • Systemically unwell OR
  • Systemically well but with complicating comorbidity
  • (e.g., peripheral arterial disease, venous insufficiency, obesity)

Class III

  • Significant systemic upset
  • Acute confusion, tachycardia, tachypnoea, hypotension
  • Unstable comorbidities interfering with treatment
  • Limb-threatening infection due to vascular compromise

Class IV

  • Sepsis
  • Severe life-threatening infection
  • Necrotising fasciitis

Differential Diagnosis

Unilateral Conditions

  • Deep venous thrombosis (pain and swelling of calves)
  • Septic arthritis (joint involvement, pain with movement)
  • Acute gout (swelling, redness, warmth, pain on movement)
  • Ruptured Baker's cyst (unilateral calf swelling)
  • Thrombophlebitis (venous inflammation with thrombus)
  • Cutaneous abscess (hot, red, swollen, painful swelling)
  • Erysipelas (superficial cellulitis with raised borders)

Chronic Conditions (Usually Bilateral)

  • Varicose eczema/venous insufficiency
  • Contact allergic dermatitis
  • Lipodermatosclerosis
  • Cutaneous small vessel vasculitis
  • Lymphoedema
  • Oedema with blisters
  • Panniculitis

Investigations

Investigations are not usually necessary but may be considered in certain cases:

Microbiological

  • Swab for culture if:
    • Open wound or penetrating injury
    • Drainage or obvious portal for microbial entry
    • Exposure to water-borne organisms
    • Infection acquired outside the UK
    • Severe cellulitis

Imaging

  • Ultrasonography to:
    • Distinguish nonpurulent cellulitis from abscess
    • Identify drainable fluid collections

Other Tests

  • Skin biopsy if:
    • Doubt about diagnosis
    • Unresponsive to initial treatment
    • Identify unusual pathogens
  • WBC, ESR, CRP to detect acute inflammation
  • Tests to exclude differential diagnoses

Management

Indications for Hospital Admission

Patients require hospital admission for IV antibiotics (first line: IV flucloxacillin 500 mg - 2 g QDS) if they:

  • Have Class III or IV cellulitis
  • Have Class II cellulitis
  • Have severe or rapidly deteriorating cellulitis
  • Are very young (<1 year) or frail
  • Are immunocompromised
  • Have significant lymphoedema
  • Have facial cellulitis (unless very mild)
  • Have suspected orbital or periorbital cellulitis
  • Are not responding to oral treatment

Outpatient Management (Class I)

Draw around the extent of infection with a permanent marker pen for future comparison

Advise patient to take analgesia, drink adequate fluids, elevate leg for comfort and edema relief

Manage breaks in the skin (eczema, tinea pedis, leg ulcers)

Prescribe oral antibiotics:

  • Adults with Class I cellulitis: flucloxacillin 500-1000 mg QDS for 5-7 days
  • Adults with infection near eyes/nose: co-amoxiclav 500/125 mg TDS for 7 days

Complications

Acute Complications

  • Deep-seated infections:
    • Necrotising fasciitis
    • Myositis
  • Sepsis
  • Subcutaneous abscesses
  • Post-streptococcal nephritis

Chronic Complications

  • Persistent leg ulceration
  • Lymphoedema (permanent lymphatic damage)
  • Recurrent cellulitis

Erysipelas

Definition

Erysipelas is a bacterial skin infection involving the upper dermis that characteristically extends into the superficial cutaneous lymphatics. It is a tender, intensely erythematous, indurated plaque with a sharply demarcated border, reflecting its more superficial nature.

Clinical Features

  • Historically occurred on the face
  • Now most often involves the legs
  • Sharply demarcated borders
  • More superficial than cellulitis

Causative Organism

  • Almost all cases caused by Group A beta-haemolytic streptococci
  • Streptococcus pyogenes

Management

  • Treat in the same way as cellulitis