Bacterial infections - folliculitis
Description
- Inflammation of the hair follicle - superficial (ostiofolliculitis) or deep (furuncle/carbuncle spectrum)
- Presents as follicular pustules/papules, each centred on a hair
- Spectrum: folliculitis -> furuncle (boil, single follicle abscess) -> carbuncle (coalescent multi-follicle abscess)
Epidemiology
- Very common; peaks in adolescence/young adulthood (shaving, occlusion, sport)
- Risk factors: shaving/waxing, occlusive clothing, hot tubs (Pseudomonas), obesity, diabetes, hyperhidrosis, immunosuppression
Aetiopathogenesis
Bacterial
- Staphylococcus aureus - commonest cause overall, incl. community-acquired MRSA
- Pseudomonas aeruginosa ("hot tub folliculitis") - contaminated spa/pool water, truncal, 1-4 days post-exposure, usually self-limiting
- Gram-negative folliculitis - complication of long-term antibiotic therapy for acne (disrupts normal flora)
Non-bacterial mimics (important differential)
- Pityrosporum (Malassezia) folliculitis - fungal, monomorphic itchy papules on trunk, does not respond to antibacterials
- Eosinophilic folliculitis - HIV-associated, intensely pruritic
- Pseudofolliculitis barbae - ingrown hairs post-shaving, not infective
Diagnosis
Clinical - usually sufficient
- Follicular-based pustules/papules +/- surrounding erythema, mild tenderness
- Furuncle: firm, tender, fluctuant nodule -> may point/discharge
- Carbuncle: larger, deeper, multiple draining points, systemic symptoms more likely (fever, malaise)
Investigations - for recurrent, atypical, or severe disease
- Swab for M/C/S - identify MRSA, guide antibiotic choice
- Consider screening for diabetes/immunosuppression with recurrent or extensive disease
- Nasal/perineal/axillary swabs +/- decolonisation protocol for recurrent staphylococcal disease
Management
A. Superficial folliculitis
- Usually self-limiting; antiseptic wash (chlorhexidine), avoid occlusion/shaving of affected area
- Topical antibiotic (mupirocin) if persistent/localised
B. Furuncle/carbuncle
- Incision and drainage is the primary treatment once fluctuant - antibiotics alone often inadequate for a collection
- Add oral antibiotics (flucloxacillin, or empirical MRSA cover if risk factors/local prevalence high, e.g. clindamycin/trimethoprim-sulfamethoxazole) if: systemic symptoms, surrounding cellulitis, immunosuppression, facial location (risk of cavernous sinus spread), or multiple lesions
C. Recurrent furunculosis
- Decolonisation: nasal mupirocin BD 5 days + chlorhexidine body wash +/- treat household contacts
- Screen for diabetes, iron deficiency, immunosuppression if recurrent
D. Hot tub (Pseudomonas) folliculitis
- Usually self-limiting over 7-10 days; ciprofloxacin only if severe/immunosuppressed
Associations
- Diabetes, obesity, hyperhidrosis
- Immunosuppression (HIV, chemotherapy) - more extensive/atypical disease
- Nasal S. aureus carriage - risk factor for recurrence
- Acne, hidradenitis suppurativa - overlapping follicular pathology
Natural history & complications
- Superficial folliculitis - typically resolves within days with hygiene measures
- Furuncle/carbuncle - risk of scarring, and rarely facial "danger triangle" lesions can seed cavernous sinus thrombosis via valveless facial veins
- Recurrent furunculosis - significant quality-of-life impact, may require prolonged decolonisation course
- Carbuncles more likely to require surgical drainage and cause systemic illness than isolated furuncles
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