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  • Bacterial infections of the skin can be classified as primary or secondary (Table 47–1). Primary bacterial infections are usually caused by a single bacterial species and involve areas of generally healthy skin (eg, impetigo and erysipelas). Secondary infections, however, 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 and, less commonly, gram-negative bacteria present on the skin surface. Staphylococcus aureus and Streptococcus pyogenes account for the majority of SSTIs. Community-associated methicillin-resistant S. aureus (CA-MRSA) has emerged and is often isolated in otherwise healthy patients.

TABLE 47–1Bacterial Classification of Important Skin and Soft-Tissue Infections


  • Erysipelas (Saint Anthony’s fire) is an infection of 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 and malaise) prior to the appearance of the lesions. The infected area is painful, often a burning pain. Erysipelas lesions are bright red and edematous with lymphatic streaking and clearly demarcated raised margins. 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 more serious infections, aqueous penicillin G, 2 million to 8 million units daily, should be administered intravenously (IV). Penicillin-allergic patients can be treated with clindamycin or erythromycin.

  • Evidence-based recommendations for treatment of SSTIs are found in Table 47–2, and recommended drugs and dosing regimens for outpatient treatment of mild to moderate SSTIs are found ...

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