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  • Bacterial infections of the skin can be classified as primary or secondary (Table 48-1). Primary bacterial infections are usually caused by a single bacterial species and involve areas of generally healthy skin (eg, impetigo and erysipelas). Secondary infections develop in areas of previously damaged skin and are frequently polymicrobic.

  • The conditions that may predispose a patient to the development of skin and soft-tissue infections (SSTIs) include: (1) a high concentration of bacteria; (2) excessive moisture of the skin; (3) inadequate blood supply; (4) availability of bacterial nutrients; and (5) damage to the corneal layer, allowing for bacterial penetration.

  • The majority of SSTIs are caused by gram-positive organisms on the skin surface. Staphylococcus aureus and Streptococcus pyogenes account for the majority of SSTIs. Other common nosocomial pathogens include Pseudomonas aeruginosa (11%), enterococci (9%), and Escherichia coli (7%).

TABLE 48-1Bacterial Classification of Important Skin and Soft-Tissue Infections


  • Erysipelas (Saint Anthony’s fire) is a distinct form of cellulitis involving the superficial layers of the skin and cutaneous lymphatics. The infection is almost always caused by β-hemolytic streptococci, with S. pyogenes (group A streptococci) responsible for most infections.

  • The lower extremities are the most common sites for erysipelas. Patients often experience flu-like symptoms (fever, chills, and malaise) prior to the appearance of the lesions. The infected area is painful, often a burning pain. The lesion is intensely erythematous and edematous, often with lymphatic streaking. It has a raised border, which is sharply demarcated from uninfected skin. Leukocytosis is common, and C-reactive protein is generally elevated.

  • Mild-to-moderate cases of erysipelas in adults are treated with intramuscular procaine penicillin G or penicillin VK for 7–10 days. For more serious infections, the patient should be hospitalized and aqueous penicillin G administered IV. Penicillin-allergic patients can be treated with clindamycin.

  • Evidence-based recommendations for treatment of SSTIs are given in Table 48-2, and recommended drugs and dosing regimens for outpatient treatment of mild-to-moderate SSTIs are given in Tables 48-3 and ...

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