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The skin consists of the superficial epidermis, dermis, and deeper subcutaneous tissues (Figure 147-1). The lymphatics run parallel with the blood vessels. Cellulitis is an infection of the deep dermis and subcutaneous fat of the skin. Erysipelas is a more superficial skin infection involving the upper dermis with prominent lymphatic involvement. Folliculitis is an infection of the hair follicle. Skin abscesses are collections of pus within the dermis and deeper skin tissues, potentially into the subcutaneous tissues. Furuncles are single, deep nodules involving the hair follicle that are often suppurative. Carbuncles are formed by multiple interconnecting furuncles that drain through several openings in the skin. Methicillin-resistant Staphylococcus aureus (MRSA) can cause any of the above disorders, and is discussed first because it is a common cause of soft tissue infections.

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Figure 147-1.
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Schematic diagram of the architecture of the skin. This diagram shows the anatomy of the skin, including the epidermis, dermis, and deeper subcutaneous tissues. Also shown are the blood vessels and a hair follicle. (Reproduced with permission from Wolff et al., Fitzpatrick’s Dermatology in General Medicine, 7th ed © 2008, McGraw-Hill, Inc., New York.)

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Epidemiology

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MRSA infections can develop in hospitalized patients, in patients with health care–related risk factors, and in otherwise healthy patients without known risk factors (Table 147-1).1,2

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Table Graphic Jump Location
Table 147-1 Risk Factors for Infections with Methicillin-Resistant Staphylococcus aureus (MRSA)
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Community-acquired MRSA (CA-MRSA) is epidemic across all populations, regardless of risk factors or geographic location.3–5 As much as 59% of purulent skin and soft tissue infections in patients >18 years old3 and up to 75% of purulent skin abscesses in children are caused by MRSA.4,5

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Pathophysiology

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CA-MRSA strains possess unique clinical and microbiologic characteristics that distinguish them from the traditional hospital-based ...

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