A 63-year-old man comes to the physician because of a 2-day history of redness, swelling, and pain of the right leg. He also has fever, chills, and nausea. He has hypertension and gastroesophageal reflux disease. His current medications include metoprolol, enalapril, and omeprazole. His temperature is 38.7°C (101.7°F), pulse is 106/min, and blood pressure is 142/94 mm Hg. Examination of the right lower leg shows a large area of erythema with poorly-demarcated borders. The area is nonfluctuant, warm, and tender to touch. Examination of the right groin shows several enlarged, tender lymph nodes. There is mild edema of the ankles bilaterally. Blood and wound cultures are collected. Infection with which of the following organisms is most likely responsible for this patient's current symptoms?

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Eductional Objective: The most common cause of nonpurulent cellulitis is beta-hemolytic streptococci, particularly group A streptococcus.  The most common cause of purulent cellulitis is Staphylococcus aureus.

A 63-Year-Old Man Comes to the Physician Because of a 2-Day