Cellulitis

Cellulitis is an acute bacterial infection involving the epidermis, dermis, and superficial subcutaneous tissue. Bacteria usually enter through a break in the skin barrier: a fissure between the toes, tinea pedis, eczema, an ulcer, insect bite, surgical wound, injection site, or minor trauma that the patient may not remember. The most common organisms are Streptococcus pyogenes, other beta-haemolytic streptococci, and Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA). Once organisms enter tissue, the local immune response produces vasodilation and increased capillary permeability. That is why the area becomes red, warm, swollen, and painful: more blood reaches the site, and fluid and inflammatory cells move out of the vessels into the tissue. The typical pattern is diffuse erythema with indistinct, non-raised borders. Erysipelas is more superficial and usually has a bright-red, sharply demarcated, raised edge. An abscess is different again: it is a localized collection of pus, often with fluctuance, a central pustule, drainage, or focal tenderness. Antibiotics may not clear a walled-off collection without drainage. Non-purulent cellulitis is more often streptococcal. Purulence, an abscess, or purulent drainage raises concern for *S....