Cellulitis is an infection of the deep dermis and subcutaneous tissue, manifesting as expanding erythema, edema, and warmth of the skin. In most instances of cellulitis, the causative microorganism cannot be definitively determined. However, based on studies using blood cultures, other laboratory markers (anti-streptolysin O and anti-DNase B antibodies), and clinical response to β-lactam antimicrobials, the vast majority of cellulitis is thought to be caused by β-hemolytic streptococci. Staphylococci, including methicillin-resistant Staphylococcus aureus (MRSA), are a less common cause of cellulitis and are more likely to be encountered in cases of purulent cellulitis (drainage or exudate in the absence of a drainable abscess) or abscess formation.3 Thus, current guidance from the Infectious Diseases Society of America advises that nonpurulent cellulitis without abscess should be treated with antimicrobials targeted primarily against streptococci.

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