Bacterial Skin Infections

Nilanthi Gunawardane

Bacterial skin infections are a common cause for visits to a health-care provider. Superficial bacterial skin infections are usually caused by staphylococci or streptococci. Risk factors for bacterial skin infections include antecedent cutaneous lesions, obesity, malnutrition, diabetes, and acquired or inherited immune dysfunction (Table 5-1).

IMPETIGO

I. BACKGROUND

Impetigo is caused primarily by Staphylococcus aureus. Other causes include group A Streptococcus or a combination of S. aureus and group A Streptococcus. Impetigo is contagious and can easily be spread through person-to-person contact or through fomites. Predisposing factors include poor health and hygiene, malnutrition, and warm climate, as well as antecedent scabies, chickenpox, contact and atopic dermatitis, and other eruptions causing skin breakdown. Postinfectious acute glomerulonephritis is quite rare in the United States (up to 5% of patients with impetigo). Nephritogenic strains of Streptococcus include serotypes 1, 4, 12, 25, and 49.

Bullous staphylococcal impetigo is seen primarily in children. It is caused by group II phage types 70 and 71 staphylococci and rarely by group A Streptococcus. These organisms elaborate an exfoliative toxin that induces a split at the granular layer of the epidermis, resulting in blister formation. This toxin may also cause an exfoliative dermatitis (Ritter disease, staphylococcal scaldedskin syndrome) in infants and children.

II. CLINICAL PRESENTATION

Impetigo is common in children and is usually located on the face and other exposed areas. Perinasal or perioral lesions may follow an upper respiratory tract infection. Impetigo begins as a small erythematous macule that rapidly develops into a fragile vesicle with an erythematous areola. The vesicopustule breaks and leaves red, oozing erosion capped with a thick, golden yellow crust (Fig. 5-1). Satellite lesions are often seen. Impetigo can be either asymptomatic or pruritic. Regional lymphadenopathy and elevated white blood cell count may be present and extensive impetigo may be seen in immunocompromised patients. Infants have a predilection for impetigo in the inguinal folds and diaper area, which may later generalize.

The presenting lesions of bullous staphylococcal impetigo are flaccid bullae that are first filled with clear, then cloudy, fluid which are replaced after rupture by a thin, varnish-like crust. Lesions may be up to 1 cm or more in diameter and may lack surrounding erythema.

TABLE 5-1 Treatment of Bacterial Skin Infections

Skin Infection	Treatment
Impetigo	a. Topical antibiotics: mupirocin, fusidic acid, and retapamulin b. Systemic antibiotics: penicillinase-resistant penicillins, cephalosporins, and macrolides c. Wound care: warm water or saline soaks
Folliculitis	a. Topical antibiotics: clindamycin, mupirocin, and antibacterial soaps b. Systemic antibiotics: penicillinase-resistant penicillins, cephalosporins, and macrolides c. Isotretinoin for gram-negative folliculitis
Cellulitis	a. Systemic antibiotics: penicillinase-resistant penicillins, cephalosporins, macrolides, and fluoroquinolones. If MRSA, trimethoprim-sulfamethoxazole, clindamycin, or tetracyclines b. Address the underlying predisposing conditions
Erythrasma	a. Systemic antibiotics: erythromycin and tetracycline b. Topical: antibiotics (clindamycin, erythromycin), antibacterial soaps, and antifungals (clotrimazole, miconazole)
Carbuncle/furuncle/abscess	a. Moist heat/warm compresses b. Incision and drainage c. Systemic antibiotics: penicillinase-resistant penicillins, clindamycin, and macrolides. If MRSA, trimethoprim-sulfamethoxazole, clindamycin, and tetracyclines d. Rigorous skin hygiene, mupirocin in nares for decolonization, and bleach baths

III. WORKUP

Most cases of impetigo need not be routinely cultured; recalcitrant or unusual cases deserve a Gram stain and culture of the exudate.

IV. TREATMENT

A. Topical Antibiotics. First-line treatment is with topical antibiotics, either mupirocin, fusidic acid, or retapamulin ointment. Mupirocin has a low rate of contact sensitization.

B. Systemic Antibiotics. If impetigo is extensive, resistant to topical treatment or for patients with comorbidities such as atopic dermatitis or immunosuppression, systemic treatment with antibiotics may be warranted. Oral penicillinase-resistant penicillins, first-generation cephalosporins (e.g., cephalexin), amoxicillin with β-lactamase inhibitor, and macrolides (e.g., azithromycin and clarithromycin) are all effective
treatments. Treatment with systemic antibiotics does not decrease the incidence of glomerulonephritis.

Figure 5-1. Impetigo. Dried stuck-on appearing “honey-crusted” lesions in a typical location. (From Goodheart HP. Goodheart’s Photoguide of Common Skin Disorders. 2nd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2003.)

C. Wound Care. The lesions should be soaked three to four times a day in warm tap water or saline solution to remove the crusts, and then dressed with antibiotic ointment.

D. Monitor Untreated, Nonbullous Impetigo. This usually resolves spontaneously without scarring in 10 to 14 days.

FOLLICULITIS

I. BACKGROUND

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