Chapter 152: Soft Tissue Infections

INTRODUCTION

This chapter discusses soft tissue infections in adults; impetigo and other soft tissue infections in children are discussed in chapter 141, "Rashes in Infants and Children."

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 (not shown in the figure). Cellulitis is an infection of the dermis and subcutaneous tissues of the skin. Cellulitis is divided clinically as purulent or nonpurulent, and management of the two types is different.^1,2 Purulent cellulitis is cellulitis with an abscess, or cellulitis with drainage or exudate in the absence of a drainable abscess. Nonpurulent cellulitis has no purulent drainage or exudate and no associated abscess.^1,2 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. However, in many countries, the term erysipelas is considered synonymous with cellulitis.² 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. Abscesses should be differentiated from simple cellulitis, because abscesses should be treated with incision and drainage.¹ Furuncles (or boils) are single, deep nodules involving the hair follicle that are often suppurative.² Carbuncles are formed by multiple interconnecting furuncles that drain through several openings in the skin.² Necrotizing soft tissue infections are necrotizing infections involving any of the soft tissue layers including the dermis, subcutaneous tissues, fascia, and muscle.³

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.^4,5 Risk factors for specific organisms causing cellulitis are listed in Table 152-2.^{1,4,6,7,8,9,10,11} Cellulitis is observed more frequently among middle-aged and elderly patients, whereas erysipelas is more common among children and elderly patients.¹² Patient characteristics demonstrate a male predominance (61%) and a mean age of 46 years, and the vast majority of infections involve either the lower or upper extremities (48% and 41%, respectively). Approximately 10% of patients diagnosed with cellulitis are hospitalized, the majority of these patients are over age ...