Impetigo is a superficial pyoderma caused by infection with staphylococci, although group A b-hemolytic streptococci may also be cultured. It is a common skin infection, primarily affecting young children, especially in warm, humid conditions. Impetigo can arise at the site of insect bites or superficial cutaneous trauma; sometimes there is no apparent predisposing skin lesion. Fever and systemic signs are uncommon.
The skin lesions start as small erythematous macules and papules. These develop into discrete, thin-walled vesicles which become pustular and quickly rupture (see
Fig 131-1). As the vesicles rupture, a yellow fluid forms an exudate, which dries to form a stratified golden, yellow crust that accumulates. The crusts can be readily removed, leaving a smooth, red surface. The crusts can spread the infection to other parts of the body. Initially, the lesions are discrete, but they may enlarge and become confluent. Local adenopathy may be present. The infection occurs most frequently on the face, neck, and extremities.
FIG. 131-1. Impetigo contagiosum. [From Marples RR, Leyden JL: Bacterial infections, section I. Fundamental cutaneous microbiology, in Moschella SL, Hurley HJ
(eds): Dermatology. Philadelphia, Saunders, 1985, vol 1, chap 11, pp 590-642, with permission.]
The diagnosis of impetigo can be readily made on the basis of the typical clinical appearance. Cultures are generally not necessary. Systemic antibiotic therapy must be combined with wound scrubbing and cleansing and application of neosporin or mupirocin ointment for optimal results. Effective antibiotics include oral antibiotics such as erythromycin, clindamycin, cephalosporins, and dicloxacillin.
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