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Skin is composed of an outermost, avascular layer of epidermis with an inner layer of dermis made up of elastic tissue, collagen, and reticular fibers. Subcutaneous tissue includes fat cells, connective tissue, and muscle. Blood vessels pass through subcutaneous tissues to reach the dermis (Figure 48-1).

Bacterial skin and soft tissue infections (SSTIs) can be subdivided into two groups: superficial and deep; another classification scheme is to distinguish between purulent and nonpurulent infections. Superficial infections tend to evolve from local spread of organisms, but can also represent circulating toxin-mediated disease (see section on special considerations). Common superficial infections include impetigo, folliculitis, carbuncles, furuncles, paronychia, cellulitis, and erysipelas (Table 48-1). Deeper infections include abscesses, necrotizing fasciitis, and pyomyositis. These infections can arise from either local spread of organisms and traumatic inoculation (abscess, necrotizing fasciitis) or hematogenous spread (pyomyositis). This chapter focuses on impetigo, cellulitis, cutaneous abscess, necrotizing fasciitis, and pyomyositis (Table 48-2). Other rashes are reviewed in Chapter 17.

TABLE 48-1Common Superficial Skin and Skin Structure Infections
TABLE 48-2Etiology of Deeper Skin and Skin Structure Infections

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