Furunculosis & Carbuncles

For further information, see CMDT Part 6-49: Furunculosis (Boils) & Carbuncles

Essentials of Diagnosis

• Extremely painful inflammatory swelling based on a hair follicle that forms an abscess

• Coagulase-positive Staphylococcus aureus is the causative organism

• Predisposing condition (diabetes mellitus, HIV disease, injection drug use) sometimes present

General Considerations

• A furuncle (boil) is a deep-seated infection (abscess) involving the entire hair follicle and adjacent subcutaneous tissue

• The most common sites of occurrence are the hairy parts exposed to irritation and friction, pressure, or moisture

• Because the lesions are autoinoculable, they are often multiple

• A carbuncle consists of several furuncles developing in adjoining hair follicles and coalescing to form a conglomerate, deeply situated mass with multiple drainage points

Demographics

• Predisposing cause usually not found

• However, diabetes mellitus (especially diabetics using insulin injections), injection drug use, allergy injections, and HIV disease all increase the risk of staphylococcal infections by increasing the rate of carriage

Symptoms and Signs

Furuncle

• Rounded or conical abscesses on the hairy parts exposed to irritation and friction, pressure, or moisture

• Lesions are often multiple and pain and tenderness may be prominent

• Lesions gradually enlarge, become fluctuant, and then soften and open spontaneously after a few days to 1–2 weeks to discharge a core of necrotic tissue and pus

Carbuncle

• Consists of several furuncles in adjoining hair follicles and coalescing to form a deeply situated mass with multiple drainage points

Differential Diagnosis

• Inflamed sebaceous (epidermal inclusion) cyst

  • Suddenly becomes red, tender, and expands greatly in size over 1 to a few days

  • History of prior cyst in the same location, presence of a clearly visible cyst orifice, and extrusion of malodorous cheesy material (rather than purulent material) helps in the diagnosis

• Acne vulgaris

• Tinea profunda (deep tinea of hair follicle)

• Sporotrichosis

• Blastomycosis

• Hidradenitis suppurativa (acne inversa)

  • Recurrent tender sterile abscesses in the axillae, groin, on the buttocks, or below the breasts

  • Presence of old scars or sinus tracts plus negative cultures suggests this diagnosis

• Anthrax

• Tularemia

Laboratory Tests

• Leukocytosis may occur, but a white blood cell count is rarely required

• Although S aureus is almost always the cause, pus can be cultured, especially in immunocompromised patients, to rule out methicillin-resistant S aureus (MRSA) or other bacteria

Medications

• Systemic antibiotics

  • Trimethoprim-sulfamethoxazole, 160/800 or 320/1600 mg orally twice a day for 10 days or 7 days, respectively, or clindamycin, 300 mg orally three times daily for 10 days, at the time of drainage

    • Have higher cure rates

    • Lower new infection rates

  • Other antibiotic options include sodium dicloxacillin or cephalexin, 1 g orally daily in divided doses for 10 days

  • For suspected MRSA, doxycycline 100 mg twice daily, trimethoprim-sulfamethoxazole double-strength one tablet twice daily, clindamycin 150–300 mg twice daily, and linezolid 400 mg twice daily for 7–10 are effective

• Recurrent furunculosis

  • Combination of cephalexin (250–500 mg four times daily) or doxycycline (100 mg twice daily) for 2–4 weeks plus either rifampin (300 mg twice daily for 5 days) or long-term clindamycin (150–300 mg daily for 1–2 months)

  • Shorter courses of antibiotics (7–14 days) plus long-term daily chlorhexidine whole body washing and intranasal, axilla, and anogenital mupirocin 2% ointment three times daily for 5 days or retapamulin 1% ointment twice daily for 5 days may also be curative

Surgery

• Incision and drainage, recommended for all loculated collections, is a mainstay of therapy

• Use surgical incision and drainage after the lesions are “mature”

Therapeutic Procedures

• Immobilize the part and avoid overmanipulation of inflamed areas

• Use moist heat to help larger lesions “localize”

Follow-Up

Recurrent furunculosis

• Culture of the anterior nares may identify chronic staphylococcal carriage in recurrent infections

• Family members, pets, and intimate contacts may need evaluation for staphylococcal carrier state and perhaps concomitant treatment

Complications

• Serious and sometimes fatal complications of staphylococcal infection such as septicemia can occur

Prevention

• Identifying and eliminating the source of infection is critical (eg, nasal carriage of Staphylococcus)

• Meticulous handwashing; no sharing of towels, clothing and personal hygiene products; avoiding loofas or sponges in the bath or shower; changing underwear, sleepwear, towels, and washcloths daily; aggressive scrubbing of showers, bathrooms and surfaces with bleach; bleach baths (1/4 to 1/2 cup per 20 L of bathwater for 15 minutes 3–5 times weekly), and isolation of infected patients who reside in institutions to prevent spread are all effective measures

• Stopping risky behavior, such as injection drug use, can also prevent recurrence of furunculosis

Prognosis

• Recurrent crops may occur for months or years

When to Refer

• If there is a question about the diagnosis, if recommended therapy is ineffective, or if specialized treatment is necessary