Cellulitis and erysipelas

Cellulitis is an infection of the deep dermis and subcutaneous tissue; erysipelas is more superficial, involving only the upper dermis and superficial lymphatics.

The most common causative bacteria are Streptococcus pyogenes and Staphylococcus aureus, but infection can be caused by Streptococcus pneumoniae, Haemophilus influenzae, gram-negative bacilli, and anaerobes.

Usually make the diagnosis based on history and examination only, although consider swab and aspiration cultures if cellulitis is associated with a break in the skin. Take blood cultures in patients who require hospital admission.

Prior episodes of cellulitis, pre-existing lymphoedema or venous insufficiency, diabetes, obesity, and tinea pedis can all predispose to this condition.

Target antibiotics at the most common causes (streptococci and S aureus) and treat predisposing conditions.

Cellulitis is an acute spreading infection of the skin with visually indistinct borders that principally involves the dermis and subcutaneous tissue. It is characterised by redness, swelling, heat, and tenderness, and commonly occurs in an extremity.

Erysipelas is a distinct form of superficial cellulitis with notable lymphatic involvement. It is raised and sharply demarcated from uninvolved skin.

Animal bites (including human bites), surgical wound infections, diabetic foot infections, and cellulitis or erysipelas in children and pregnant women are beyond the scope of this topic. See Animal bites and Diabetes-related foot disease.