Dermatology · Infectious Dermatoses
The facts most likely to be tested
Staphylococcus aureus is the most common infectious pathogen causing superficial folliculitis.
Clinical presentation involves erythematous papules or pustules centered around a hair follicle.
Hot tub folliculitis is specifically caused by Pseudomonas aeruginosa following exposure to contaminated water.
Gram-negative folliculitis typically occurs in patients on long-term antibiotic therapy for acne vulgaris.
Malassezia folliculitis presents as monomorphic, pruritic papulopustules on the upper trunk and is caused by yeast overgrowth.
Treatment for mild, localized bacterial folliculitis consists of topical mupirocin or clindamycin.
Extensive or recalcitrant cases of folliculitis require systemic therapy with oral anti-staphylococcal antibiotics like cephalexin or dicloxacillin.
Vignette unlocked
A 24-year-old male presents to the clinic with a 3-day history of a rash on his chest and back. He recently returned from a vacation where he spent significant time in a communal hot tub. Physical examination reveals numerous erythematous papules and pustules distributed primarily on his trunk, sparing the face. The lesions are tender and centered around hair follicles. He is otherwise afebrile and systemically well.
What is the most likely causative organism?
Pseudomonas aeruginosa
The patient's history of hot tub exposure combined with the distribution of follicular pustules is classic for hot tub folliculitis, which is caused by Pseudomonas aeruginosa.
Full handout
High yield triage
Etiology / Epidemiology
Commonly caused by Staphylococcus aureus; hot tub folliculitis is caused by Pseudomonas aeruginosa.
Clinical Manifestations
Presents as perifollicular papules and pustules; hot tub folliculitis involves pruritic lesions in bathing suit distribution.
Diagnosis
Primarily a clinical diagnosis; bacterial culture is the gold standard if refractory.
Treatment
First-line is topical mupirocin or topical clindamycin; avoid systemic antibiotics for mild cases.
Prognosis
Self-limiting; furuncles or carbuncles are potential complications if infection deepens.
Full handout
Epidemiology & Etiology
Most cases are bacterial, with Staphylococcus aureus being the most common pathogen. Hot tub folliculitis is a distinct variant caused by Pseudomonas aeruginosa following exposure to contaminated water. Risk factors include occlusion, hyperhidrosis, and chronic topical corticosteroid use.
Pertinent Anatomy
The infection is localized to the hair follicle infundibulum. Involvement of the entire follicle and surrounding dermis leads to the formation of a furuncle.
Pathophysiology
Mechanical or chemical irritation causes follicular damage, allowing bacterial colonization. The host inflammatory response results in the formation of a pustule centered on a hair follicle. If the infection breaches the follicular wall, it progresses to a deeper abscess.
Clinical Manifestations
Patients present with erythematous papules or pustules centered on hair follicles. Hot tub folliculitis presents as pruritic, erythematous papules in areas covered by a swimsuit. Red flags include systemic symptoms like fever or cellulitis spreading beyond the follicular site.
Diagnosis
Diagnosis is clinical. A bacterial culture of the pustule is the gold standard for identifying resistant organisms like MRSA in recurrent or treatment-refractory cases.
Treatment
Mild cases require topical mupirocin or topical clindamycin. For extensive or refractory cases, oral cephalexin or dicloxacillin is indicated. Avoid systemic antibiotics for simple cases to prevent resistance. For Pseudomonas, ciprofloxacin may be required in severe cases.
Prognosis
Most cases resolve within 7-10 days with proper hygiene. Furuncles and carbuncles are the primary complications requiring incision and drainage.
Differential Diagnosis
Acne vulgaris: comedones present
Pseudofolliculitis barbae: inflammatory reaction to ingrown hairs without infection
Keratosis pilaris: follicular plugging without pustules
Eosinophilic folliculitis: associated with HIV/immunocompromise
Tinea barbae: fungal infection requiring KOH prep