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Chapter 45. Skin and Skin Structure Infections

Matthew Kronman

Skin is composed of an outermost, avascular layer of epidermis with an inner layer of dermis made up of elastic tissue, collagen, and reticular fibers. Subcutaneous tissue includes fat cells, connective tissue, and muscle. Blood vessels pass through subcutaneous tissues to reach the dermis (Figure 45–1).

Figure 45–1.
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Basic skin anatomy.

Bacterial skin and skin structure infections (SSIs) can be subdivided into two groups: superficial and deep (Figure 45–1). Superficial infections tend to evolve from local spread of organisms, but can also represent circulating toxin-mediated disease. Common superficial infections include impetigo, folliculitis, carbuncles, furuncles, paronychia, cellulitis, and erysipelas (Table 45–1). Deeper infections include abscess and pyomyositis and instead tend to arise by the hematogenous spread of organisms from a distant site. This chapter will review cellulitis, cutaneous abscess, and pyomyositis (Table 45–2).

Table 45–1. Common Superficial Skin and Skin Structure Infections
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Table 45–1. Common Superficial Skin and Skin Structure Infections

Disease

Definition

Most Common Causes

Less Common Causes to Consider

Treatment

Impetigo

Well-localized superficial skin infection with or without bulla formation

MSSA, GABHS

Topical mupirocin or retapamulin; Oral clindamycin, cephalexin, erythromycin, or amoxicillin plus clavulanic acid for 7–10 d

Folliculitis

Collection of superficial infections in hair follicles without deeper involvement

MSSA

Pseudomonas, coagulase-negative staphylococci

Warm compresses, topical mupirocin, retapamulin or chlorhexidine; oral cephalexin or dicloxacillin for severe cases for 7–10 d

Furuncle

Microabscess arising at a hair follicle in slightly deeper tissue than folliculitis

MSSA, MRSA

Hot, wet compresses; surgical drainage; oral clindamycin (if MRSA suspected) or cephalexin for 7–10 d

Carbuncle

Organized collection of adjacent furuncles; may have multiple areas of drainage

MSSA, MRSA

Hot, wet compresses; surgical drainage; oral clindamycin (if MRSA suspected) or cephalexin for 7–10 d

Paronychia

Infection of the skin surrounding the nail bed

MSSA, GABHS

Candida, Anaerobes, Streptococcus viridans, Pseudomonas, Proteus, Moraxella, Klebsiella, Eikenella

Warm compresses; surgical drainage (for deeper lesions); oral clindamycin or amoxicillin–clavulanate for 7–10 d

Erysipelas

Superficial form of cellulitis with distinct margins and involving lymphatics

GABHS

MSSA, S. pneumoniae, Klebsiella pneumoniae, Yersinia enterocolitica

Local skin care; parenteral penicillin initially, oral cephalexin or clindamycin (if staphylococci suspected) for a total length of 10 d

MSSA, methicillin-sensitive Staphylococcus aureus; MRSA, methicillin-resistant Staphylococcus aureus; GABHS, group A β-hemolytic streptococci.

Table 45–2. Etiology of Skin and Skin Structure Infections
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Table 45–2. Etiology of Skin and Skin Structure Infections

Disease

Definition

Most Common Causes

Less Common Causes to Consider

Cellulitis

Indistinctly bordered infection of subcutaneous tissue and dermis

MSSA, MRSA, GABHS

GBS (patients <3 months old), H. influenzae,Pseudomonas, Serratia, Salmonella, Nocardia, Mycobacteria, Pasteurella

Abscess

Discrete collection of pus and cellular debris separated from its surroundings by a fibrinoid wall

MSSA, MRSA, ...

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