Cellulitis

Cellulitis is a deep infection of the skin; it results in dermal erythema. The affected area is red, warm, indurated (hard) and tender. The responsible organisms are usually Staphylococcus aureus or Streptococus pyogenes (Group A streptecocci). Prior to the advent of a vaccine, Haemophilus influenzae was the most common cause of facial cellulitis in young children; Streptococus pyogenes is now the more likely culprit. There may be a history of trauma to the affected area (creating a port of entry for the bacteria). In adults, the lower extremities are commonly involved; tinea pedis or venous insufficiency may be contributing factors. Patients usually have fever and are systemically sick.

With what can it be confused?

Contact dermatitis also causes erythema, but there is usually pruritus, epidermal vesicles, and a an absence of fever. In the lower extremities, superficial thrombophlebitis (inflammation of the superficial veins) can cause erythema and tenderness, but without fever. The affected vein is often detected as a palpable "cord". In children, the rash of erythema infectiosum, a viral exanthem, can be confused with cellulitis. However, the former condition is bilateral, whereas cellulitis is typically focal. Also, the rash of erythema infectiosum is not usually tender.

How is it diagnosed?

The diagnosis is usually suspected on clinical grounds. Blood and skin cultures are often obtained, but the diagnostic yield is not high. The technique of skin culture is important; best results are obtained by injecting the edge of the involved area with saline (nonbacteriostatic) and then aspirating the fluid. A skin biopsy is usually not necessary, but it increases the diagnostic yield of culture and may be useful in resistant cases or in immunocompromised patients.

How is it treated?

Systemic antibiotics are necessary to treat the infection. Mild cellulitis may be treated with oral antibiotics, while more serious cases require intravenous antibiotics and hospitalization. Antibiotics with activity against staphylococcus aureus are necessary such as cephalexin (Keflex), dicloxacillin, or nafcillin. In resistant cases, or in the immunocompromised, gram negative coverage may be warranted. Children with facial cellulitis should receive coverage for Haemophilus influenzae is necessary (e.g. amoxicillin and clavulanate (Augmentin) plus ceftriaxone (third generation cephalosporin). For all cases, warm compresses to the affected area may be helpful.

What is the prognosis?

With treatment, otherwise healthy patient's usually defervesce within 24 hours. Persistence of fever beyond two days should prompt a reevaluation of treatment. Skin inflammation resolves over 1-2 weeks. Sepsis is often present at the time of presentation, and without treatment can prove deadly. Facial cellulitis in children may stem from, or lead to, otitis media. Meningitis occasionally occurs. Damage to lymphatics may occur from the infection, predisposing to lymphadema and recurrent episodes of cellulitis. In immunocompromoised patients (e.g HIV or transplant patients) cellulitis can still be fatal.

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Wikipedia: Several photos and subject entry.