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Impetigo is a primary superficial infection of the skin. It is more prevalent in humid climates and occurs most commonly in the summer months. Trauma to the skin, such as a small abrasion or insect bite, sometimes provides the site of entry for the infective bacteria. The lesions evolve from discrete small vesicles into pustules. The fluid content of the primary lesions dries into a thick yellowish crust (Fig. 3-1), and removal of the crust may reveal bright-red and shiny erosions (Fig. 3-2). The most common cause of impetigo is Staphylococcus aureus. When caused by Streptococcus, it may be associated with epidemics of impetigo-induced glomerulonephritis. Because the “honey-crusted” lesions of impetigo are frequently caused by a combination of Staph. aureus and Strep. pyogenes, systemic antibiotic therapy should be effective against both organisms. The use of topical mupirocin ointment appears to be an effective treatment and may replace the need for systemic therapy in some patients with localized lesions.

This form of impetigo consists of flaccid blisters that quickly rupture and evolve into superficial round or oval erosions with a varnished surface and minimal crust. Blisters are caused by the local effect of staphylococcal toxin. Pictured in Fig. 3-3 are blisters and superficial erosions. Figure 3-4 shows the collarettes of scale following rupture of the bullae. Bullous impetigo is associated with a pure culture of Staph. aureus. Oral treatment with dicloxacillin or a cephalosporin is an effective mode of therapy.

Impetigo is the most superficial of pyodermas; ecthyma is the next grade in depth. If impetigo is infection by streptococci and/or staphylococci superficially in the epidermis, ecthyma is infection by the same organisms through the entire thickness of the epidermis (0.1 mm) to the upper reaches of the dermis (perhaps to a depth of 0.5 mm). The lesion of ecthyma then becomes not a bulla but a firm crust on a superficial ulcer, surrounded by erythema.

This condition is one that is seen usually at 3–5 days of age, more commonly in males. It is characterized by discrete pustules with a slight erythematous base located in the diaper area, in the periumbilical area, on the lateral aspect of the chest, and on the neck. The condition may be seen in an epidemic setting. The diagnosis is made by doing a Gram stain and culture of a pustule. Treatment is with a systemic β-lactamase-resistant antibiotic.

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