Cellulitis & Erysipelas

Definition

Cellulitis is an acute bacterial infection of the dermis and subcutaneous tissue, whereas erysipelas is a superficial variant with well-demarcated, raised, erythematous plaques. Both conditions commonly result from bacterial entry through breaches in the skin.

Epidemiology

• Common worldwide; incidence ~200 cases per 100,000 population per year
• More common in adults and elderly
• Risk factors include diabetes, immunosuppression, venous insufficiency, lymphedema, and skin barrier disruption
• Lower extremities most commonly affected
• Recurrent episodes occur in patients with chronic edema or previous cellulitis

Etiology

• Cellulitis: usually caused by Streptococcus pyogenes (group A) and Staphylococcus aureus (including MRSA)
• Erysipelas: primarily Streptococcus pyogenes
• Entry through cuts, insect bites, ulcers, surgical wounds, tinea infections
• Predisposing factors: chronic edema, obesity, venous insufficiency, immunosuppression

Pathophysiology

• Bacteria enter through skin barrier disruption
• Infection spreads in dermis and subcutaneous tissue, triggering inflammation
• Erysipelas involves upper dermis and superficial lymphatics with sharply demarcated borders
• Inflammatory response causes erythema, warmth, edema, and tenderness
• Systemic inflammatory response may lead to fever and malaise