Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.

A 20-year-old male college student on the wrestling team is evaluated for a superficial skin infection. He has a history of several episodes of folliculitis and furunculosis over the past year that has required systemic treatment. His recurrent infections were treated with various oral antibiotics, including cephalexin, clindamycin, and trimethoprim-sulfamethoxazole. He currently takes no medications, has no drug allergies, and is otherwise in good health.

On physical examination, vital signs are normal. There are multiple, scattered erythematous papulopustules and nodules on the buttocks and upper thighs, some with a collarette of scale. He has no background erythema or lymphadenopathy. The remainder of the physical examination is unremarkable.

Which of the following is the most appropriate next step in management?

A. Culture a pustule
B. Perform a Tzanck smear
C. Start linezolid
D. Start vancomycin

MKSAP Answer and Critique

The correct answer is A. Culture a pustule.

The most appropriate first step in management is to culture a pustule to identify the causative organism prior to institution of antibiotic therapy. Bacterial skin infections are most commonly caused by Staphylococcus and Streptococcus spp. and may present in a variety of ways. This patient has recurrent folliculitis and furunculosis but is otherwise healthy. The history of recurrent infections and being part of a wrestling team would suggest that infection may be secondary to community-acquired methicillin-resistant Staphylococcus aureus (MRSA). Community-acquired MRSA, defined as MRSA infections that occurs in the absence of health care exposure, tends to have enhanced virulence compared with other strains and is currently the most common organism causing skin infection requiring medical therapy. However, because of the recurrent nature of the patient’s skin infections and his exposure to previous courses of antibiotics, a culture to identify the causative organism and its susceptibility pattern would be the most appropriate next step to guide further management.

In addition to systemic therapy, topical antibiotic therapies, including benzoyl peroxide wash, chlorhexidine, or topical mupirocin, can be used. Bleach baths may be a treatment option (put 1/4 to 1/2 cup of common liquid bleach into the bath water to create a chlorinated bath), which decreases colonization of S. aureus).

A Tzanck smear can be performed if a herpes simplex virus or varicella infection is suspected. Both infections can occur in wrestlers but would typically present as painful vesicles or punched-out erosions as opposed to furuncles or folliculitis.

Linezolid is effective against many strains of MRSA and streptococci. However, its use should be limited to patients with a documented infection who have not benefitted from sensitive antibiotics because of potential toxicities or cost. Oral cephalexin (or other cephalosporins or penicillins) should not be used because these antibiotics would not be effective against MRSA if used empirically. In addition, antimicrobial therapy in this patient would more appropriately be guided by culture and sensitivity results.

Parenteral therapy for skin and soft-tissue infections should be considered in patients with extensive involvement, in patients with evidence of systemic involvement, or patients who are immunocompromised. Although vancomycin is effective against possible MRSA, parenteral therapy would not be appropriate in a stable, otherwise healthy man without any signs of systemic infection, particularly without a confirmed MRSA infection.

Key Point

• In managing a superficial skin infection, a culture of the pustule is important to determine both the causative organism and the antibiotic susceptibility pattern.

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