A 22-year-old man comes to the office due to several small, pruritic skin pustules on his lower extremities. The patient first noticed the lesions a week ago during a trip to New Mexico, where he hiked in the mountains and swam in a heated hotel pool. He was given trimethoprim-sulfamethoxazole at an urgent care center, but the pustules have persisted despite taking the medication as prescribed for 3 days. The patient has no chronic medical conditions and takes no other medications. Temperature is 37.9 C (100.2), blood pressure is 132/68 mm Hg, and pulse is 96/min. Examination shows several small, tender papulopustules on the bilateral lower extremities. Which of the following pathogens is the most likely cause of this patient's symptoms?

Question

A 22-year-old man comes to the office due to several small, pruritic skin pustules on his lower extremities.  The patient first noticed the lesions a week ago during a trip to New Mexico, where he hiked in the mountains and swam in a heated hotel pool.  He was given trimethoprim-sulfamethoxazole at an urgent care center, but the pustules have persisted despite taking the medication as prescribed for 3 days.  The patient has no chronic medical conditions and takes no other medications.  Temperature is 37.9 C (100.2), blood pressure is 132/68 mm Hg, and pulse is 96/min.  Examination shows several small, tender papulopustules on the bilateral lower extremities.  Which of the following pathogens is the most likely cause of this patient's symptoms?

Quizplus · Accepted Answer

This patient developed a tender papulopustular eruption on his lower extremities after swimming in a heated hotel pool, raising strong suspicion for Pseudomonas aeruginosa folliculitis ("hot-tub" folliculitis). Most cases develop within hours or a few days after swimming in an inadequately chlorinated swimming pool or hot tub. The rash that forms is generally tender and may appear as papules, pustules, or nodules. Low-grade fever is often present. The eruption is usually self-limited and does not require treatment. However, patients should be advised to avoid the contaminated water that led to this condition. If lesions persist, an oral fluoroquinolone may be considered. Although Staphylococcus aureus is the leading cause of purulent skin infection (and folliculitis), most cases are sensitive to trimethoprim-sulfamethoxazole (TMP-SMX) and are marked by a purulent lesion with surrounding erythema and induration. The presence of several papulopustular lesions that did not respond to TMP-SMX make this pathogen less likely (Choice B). (Choice A) Group A Streptococcus (eg, Streptococcus pyogenes) is the leading cause of cellulitis. Most cases present with spreading erythema, warmth, and tenderness at a site of skin breakdown (eg, fungal infection, wound). Purulent lesions are less common and generally indicate an alternate pathogen. (Choice D) Sporothrix schenckii is a dimorphic fungus found in soil that can occasionally cause cutaneous infection after being introduced into the skin during gardening or other outdoor activities. However, infections usually take weeks to develop and generally present with an ulcerative papule at the site of inoculation; subsequent lesions form along the proximal lymphatic chain. This patient's bilateral papulopustular eruption on the lower extremities makes Pseudomonas folliculitis far more likely. (Choice E) Vibrio vulnificus is a estuarine bacteria that causes cellulitis following inoculation into a wound. This organism lives in marine environments, not hotel pools, and usually causes a spreading cellulitis similar to S pyogenes. Educational objective: Pseudomonas folliculitis is a self-limited cutaneous eruption that develops within hours or a few days following exposure to inadequately chlorinated pools or hot tubs. Patients generally have tender papules, pustules, or nodules and low-grade fever. No treatment is usually necessary, but swimming in the contaminated water should be avoided.

A 22-Year-Old Man Comes to the Office Due to Several