The major findings are local erythema and tenderness, frequently with lymphangitis and regional lymphadenopathy. Vesicles and bullae may develop and rupture, occasionally with necrosis of the involved skin. Leukocytosis is common but not constant. The diagnosis usually depends on the clinical findings. Unless pus has formed or an open wound is present, the responsible organism often is difficult to isolate, even on aspiration or skin biopsy.
Blood cultures are occasionally positive.
Serologic tests, especially measurement of rising titers of anti-DNase B, confirm a streptococcal cause but are usually unnecessary. Course and Prognosis Local abscesses form occasionally, requiring incision and drainage. With antibiotics, such complications are uncommon. Symptoms and signs of superficial cellulitis usually resolve after a few days of antibiotic therapy. 250 to 500 mg po qid or a single dose of benzathine penicillin 1.2 million U IM is adequate.