A 19-year-old man has a history of athlete’s foot but is otherwise healthy when he develops sudden onset of fever and pain in the right foot and leg. On physical examination, the foot and leg are fiery red with a well-defined indurated margin that appears to be rapidly advancing. There is tender inguinal lymphadenopathy. Which organism is the most likely cause of this infection?A) Staphylococcus epidermidis
Erysipelas, the cellulitis described, is typical of infection caused by S pyogenes (group A β-hemolytic streptococci). There is often a preceding event such as a cut in the skin, dermatitis, or superficial fungal infection that precedes this rapidly spreading cellulitis. Patients are usually febrile and may appear toxic. Staphylococcus epidermidis does not cause rapidly progressive cellulitis. Staphylococcus aureus can cause cellulitis that is difficult to distinguish from erysipelas, but it is usually more focal and likely to produce furuncles, or abscesses. Tinea infections spread slowly and are confined to the epidermis; they would not cause fever, dermal edema, or tender lymphadenopathy. Anaerobic cellulitis is more often associated with underlying diabetes. α-Hemolytic streptococci rarely cause skin and soft tissue infections.