Impetigo

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Clinical Presentation

Impetigo is a skin infection commonly found in children of preschool age, but may also occur in adults. Impetigo accounts for about 10% of all pediatric skin problems (4). It typically spreads from one part of the body to another through scratching and is a highly communicable disease.

Impetigo has two classic forms: nonbullous and bullous. The nonbullous form is more common and accounts for approx 70% of cases. This form is commonly associated with a "honey-colored" crusted discharge. As intact skin is resistant to this form of infection, lesion of nonbullous impetigo commonly begin on the skin of the face or extremities following even minor trauma. Common lesions that precede nonbullous impetigo include chickenpox, insect bites, abrasions, lacerations, and burns. The differential diagnosis of nonbullous impetigo includes viral, fungal, and parasitic infections.

Bullous impetigo, a disease of mainly infants and young children, may appear purulent and, when the blister is removed, the area resembles scalded skin. Flaccid, transparent bullae develop most commonly on skin of the face, buttocks, trunk, perineum, and extremities. These skin lesions may have associated adenopathy, leukocytosis, and pruritus with no or minimal systemic symptoms or signs. Lesions are associated with little or no pain or surrounding erythema.

The clinical presentation of impetigo evolves in an orderly fashion from a small vesicle or pustule, which progresses into a honey-colored crusted plague (1). Lesions usually are <2 cm in diameter. In general, lesions produce minimal symptoms. Associ-

From: Management of Antimicrobials in Infectious Diseases Edited by: A. G. Mainous III and C. Pomeroy © Humana Press Inc., Totowa, NJ

Table 1

Bacterial Causes of Common Skin and Skin Structure Infections

Lesion

Commonly Associated Bacteria

Impetigo Nonbullous Bullous Cellulitis/erysipelas

Folliculitis/furunculosis/carbuncle Animal bites Cats Dog

Humans

Streptococcus pyogenes and/or Staphylococcus aureus

Streptococcus pyogenes Staphylococcus aureus Staphylococcus aureus

Pasteurella multocida subsp. multocida and septica

Pasteurella canis

Staphylococcus aureus

Bacteroides spp.

Eikenella comodens

Fusobacteria

Peptostreptococcus

Staphylococcus aureus

Data from ref. 54.

ated findings include lymphandenopathy and leukocytosis. Lesions usually resolve in 2-3 wk without treatment and do not generally leave a scar.

Epidemiology

Impetigo is predominately found in preschool-aged children. It is a highly contagious disease and often results in outbreaks.

Etiology

Previously, impetiginous lesions were primarily of streptococcal origin. Currently, most cases of impetigo in the United States involve Staphylococcus aureus or a combination of S. aureus and streptococci (5). Bullous impetigo is most always caused by coagulase-positive S. aureus, although it has been found to be caused by 8-hemolytic streptococci Group A (6).

Treatment

Untreated impetigo may take several weeks to resolve, with spreading and development of new lesions during the resolution period. Scarring rarely occurs.

This infection may be treated either with topical or systemic antiinfective agents (Table 2). The topical treatment of impetigo with mupirocin ointment has a response rate of 85-97% (7,8). Topical mupirocin is effective in 90% of cases and is more effective than oral erythromycin (9). Topical mupirocin has not been compared to commonly used oral antibiotics.

Impetigo may be treated systemically with an oral, semisynthetic penicillin that is penicillin resistant or a first-generation cephalosporin. Most clinicians recommend either dicloxacillin or cephalexin. The failure rate of erythromycin in the presence of resistant S. aureus is 47% (9).

Recommended Initial Antibiotic Management for Common Skin Infections

Diagnosis

Antibiotic(s) of First Choice

Alternative Antibiotics

Impetigo— nonbullous

2% Mupirocin ointment three times daily 250-500 mg Cefalexin four times daily 250-500 mg Dicloxacillin four times daily

Erythromycin Azithromycin Clarithromycin Clindamycin

Impetigo—bullous

250-500 mg Cefalexin four times daily 250-500 mg Dicloxacillin four times daily

Erythromycin Azithromycin Clarithromycin Clindamycin

Cellulitis/erysipelas

Mild to moderate infection:

250-500 mg Cefalexin four times daily

250-500 mg Dicloxacillin four times daily

Erythromycin Azithromycin Clarithromycin Clindamycin

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