Common Bacterial Skin Infections

M. H. Lupin, BSc, MD, FRCPC
Department of Dermatology and Skin Science, University of British Columbia, Vancouver, Canada

The skin has a complex flora with the number of microorganisms far outnumbering the number of human cells, and infections can result when there is a breakdown in the integrity of the skin, or our immune defense is compromised.

Classification

There may be a continuum of these various infections in any one individual. Cultures and sensitivities are recommended for suspected skin infections especially with the increase of community acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). These infections can affect healthy children and can be potentially life threatening.

Types

Impetigo and Ecthyma

• Typically honey-colored crust with erythematous vesicles, papules, pustules or erosions; common area around nose and face
• More common in atopic dermatitis
• Ecthyma is a deeper version of impetigo, more commonly seen in patients with malnutrition and/or poor hygiene - vesicles and bullae, deep ulcers; legs are the most common and healing leaves scars.
• Consider insect bites, eczema, herpes, and candida and thermal burns in the differential diagnosis.
• Swab for culture and sensitivity.

Treatment
• Nonbullous: fusidic acid (Fucidin® 2% Cream) t.i.d. or mupirocin (Bactroban® Cream) t.i.d.
• Bullous or extensive or multiple lesions: fever or constitutional symptoms, + nodes, immunocompromised, valvular heart disease: cloxacillin (Cloxapen®) 40–50mg/kg/d divided (div) q.i.d., or cephalexin (Keflex®) 40mg/kg/d div q.i.d., or erythromycin 40mg/kg/d div q.i.d.

Folliculitis, Furunculosis, and Carbunculosis (Folliculitis Group)

• A spectrum of infections involving the hair follicles.
• Often characterized by asymptomatic or mildly pruritic red follicular based papules and pustules.
• Hot tub folliculitis is less common and due to Pseudomonas aeruginosa. It usually clears spontaneously and is commonly distributed over the trunk, buttocks, and thighs.
• Furunculosis is deeper, presenting with tender, erythematous nodules and suppurative drainage
• Carbuncles are a coalescence of furuncles presenting as larger, tender, fluctuant, draining nodules.
• Swab for culture and sensitivity.

Treatment
• Warm compresses for 10–15 minutes q.i.d. may give relief.
• Bacterial folliculitis and bacterial paronychia
• Fusidic acid 2% cream, t.i.d.
• Cloxacillin 40–50mg/kg/d div q.i.d., or cephalexin 40mg/kg/d div q.i.d., erythromycin 40mg/kg/d div q.i.d. All would be used for 1 week.
• Recurrent Furunculosis – Consider Staphylococcus nasal carriage;
• Mupirocin 2% cream b.i.d. intranasally for 5 days. MRSA resistance is increasing in Canada and fusidic acid unguent could be considered in those cases.
• Carbuncles
• Cloxacillin 40–50mg/kg/d div q.i.d. or cephalexin 40mg/kg/d div q.i.d.
• MRSA or penicillin allergy: clindamycin 20mg/kg/d po q.i.d. or trimethoprim/sulfa 6–12mg/kg/d po div b.i.d. for 1 week.

Abscess

• Fluctuant cystic nodule, may have a pointing pustule, usually caused by S. aureus.
• Incision and Drainage (I&D) is very important, as well as taking cultures and sensitivities.
• If there is a cellulitic component greater than 5cm, if abscess cannot easily be drained, if location is on face, or if there are systemic symptoms (fever, chills), add a systemic antibiotic.
• Suspect community acquired MRSA.

Treatment
• I & D; warm compresses for 10–15 minutes q.i.d. may give relief.
• Fusidic acid 2% cream, t.i.d., is indicated and is useful especially in smaller lesions alone or most commonly in combination.
• Cloxacillin 40–50mg/kg/d div q.i.d., or cephalexin 40mg/kg/d div q.i.d., or erythromycin 40mg/kg/d div q.i.d. for 1 week.
• MRSA or penicillin allergy: clindamycin 20mg/kg/d po q.i.d. or trimethoprim/sulfa 6–12mg/kg/d po div b.i.d. for 1 week.

Erysipelas and Cellulitis

• Erysipelas is a superficial infection with a predilection for young children and the elderly.
• Abrupt onset of tender, well-defined erythematous, indurated plaques most commonly on the face or legs. Involvement of the dermis and often the lymph nodes, usually S. pyogenes.
• Cellulitis is a deeper process extending to the subcutis. In children the head and neck is usually involved; caused by S. aureus, and less commonly, H. influenzae
• Strep perianal disease is usually seen in those under 4 years old. Well-defined redness extends up to 2–3cm away from the anus. Pharyngitis may precede it. Local discomfort/itching can be present.
• Pain inhibiting defecation may lead to fecal retention and overflow soiling or blood stains on the underwear. Psoriasis or candida should be considered as alternatives.
• Orbital, umbilical, or neonatal cellulitis will not be considered.

Treatment
• Face: Cephalexin 40mg/kg/d po div q.i.d. for 10–14 days will usually be adequate for S. aureus, H. influenza. Those under the age of 5 years could be treated with cefuroxime 100–150mg/kg/d q8h for 10–14 days. For those over 5, cefazolin 75mg/kg/d IV div q8h for 10–14 days. Clindamycin for those with â-lactam allergy.
• Perianal cellulitis: this can be polymicrobial. Amoxicillin-clavulanate 40mg/kg/d po for 10–14 days for mild cases. Clindamycin plus gentamicin or cefazolin plus metronidazole can be used depending on the culture results.[Blondel-Hill E, Fryters S, Editors. Bugs & Drugs. Edmonton: Capital Health (2000).]

Bacterial Resistance

• Due to increased bacterial resistance to drugs in general, always obtain culture and sensitivity.
• In 2005, a five-fold increase in MRSA was noted in Canada and the US.
• A recent presentation at the Canadian Association for Clinical Microbiology and Infectious Disease conference reported high (96%) MRSA sensitivity to topical fusidic acid.
• The Centre for Disease Control recommended that MRSA be a reportable disease.
• CA-MRSA is usually resistant in vitro to ß-lactams (penicillin and cephalosporins) as well as macrolides/azalides (erythromycin, clarithromycin, azithromycin).
• CA-MRSA can be sensitive to TMP/SMX (trimethoprim/sulfamethoxazole), tetracyclines (e.g., doxycycline (Doryx^®), minocycline (Minocin^®)) and clindamycin (Cleocin^®) though resistance can occur.
• Hospital acquired MRSA (HA-MRSA) is usually resistant in vitro to multiple classes of antibiotics.
• Canadian Committee on Antibiotic Resistance, www.ccar-ccra.com, is a good reference for up-to-date information on resistance patterns.

PEARLS

Nasal carriage of Staphylococcus aureus is approximately 20%–30%, so it is important to treat the nose if there is frequent recurrence of infection or there is an outbreak in close family members. Mupirocin cream q.h.s. for 6 weeks is helpful. Fusidic acid 2% cream is also effective. Rifampin can be added if topicals are insufficient. Routine treatment of the nose is not recommended.

Conclusion

Selecting the right therapy from the beginning should help minimize complications, reduce the number of hospitalizations, and may also help reduce the climbing incidence of bacterial resistance.

• Table of Contents
• The Bottom Line – Managing Diaper Dermatitis
• Treatment of Head Lice
• Common Bacterial Skin Infections