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INTRODUCTION

More than 4 in 100 people seek treatment for skin and soft tissue infections each year in the United States, and these infections are about 20 times more likely to be ambulatory treated than inpatient treated.1 Abscess or cellulitis are the most common of these infections, with the majority of patients treated in the outpatient setting.1 This chapter discusses skin and soft tissue infections in adults; impetigo and other soft tissue infections in children are discussed in Chapter 142, “Rashes in Infants and Children.” Perirectal abscess and pilonidal abscess are discussed in Chapter 85, “Anorectal Disorders.” Bartholin gland abscess is discussed in Chapter 102, “Vulvovaginitis.” Hidradenitis suppurativa is discussed in Chapter 252, “Skin Disorders: Groin and Skinfolds.” Paronychia and felons are discussed in Chapter 283, “Nontraumatic Disorders of the Hand.”

ANATOMY AND DEFINITIONS

The skin consists of the superficial epidermis, dermis, and deeper subcutaneous tissues including fat (Figure 152-1). The lymphatics run parallel with the blood vessels. Cellulitis is an infection of the dermis and subcutaneous tissue and is divided clinically as purulent or nonpurulent. Management of the two types is different.2,3 Purulent cellulitis is a skin or soft tissue infection with purulent drainage or an underlying abscess. Nonpurulent cellulitis has no purulent drainage or exudate and no associated abscess.2,3 Erysipelas traditionally has been defined as a more superficial skin infection involving the upper dermis with clear demarcation between involved and uninvolved skin with prominent lymphatic involvement. Folliculitis is an infection of the hair follicle, often purulent, but is superficial without involvement of the deeper tissues. Skin abscesses are collections of pus within the dermis and deeper skin tissues, potentially involving the subcutaneous tissues. Furuncles (or boils) are single, deep nodules involving the hair follicle that are often suppurative.3 Carbuncles are formed by multiple interconnecting furuncles that drain through several openings in the skin.3 Necrotizing soft tissue infections are characterized by microbial triggered necrosis involving any of the soft tissue layers including the dermis, subcutaneous tissues, fascia, and muscle.4

FIGURE 152-1.

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 K, et al: Fitzpatrick’s Dermatology in General Medicine, 7th ed. © 2008, McGraw-Hill, Inc., New York.]

CELLULITIS AND ERYSIPELAS

EPIDEMIOLOGY

Cellulitis accounts for approximately 1.3% of all ED visits. General risk factors for cellulitis are listed in Table 152-1.5,6 Risk factors for specific organisms causing cellulitis are listed in Table 152-2.2,5,7-12 Cellulitis is observed more frequently among middle-aged and elderly ...

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