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Home Books Review of Medical Microbiology & Immunology: A Guide to Clinical Infectious Diseases, 16e

Chapter 77: Infections of the Skin & Skin Structures

INTRODUCTION

Infections of the skin and skin structures are some of the most common infectious diagnoses and result in hundreds of thousands of medical office and emergency room visits each year. These infections often occur following a break in normal skin integrity from either trauma or skin disease (e.g., atopic dermatitis). The vast majority of these infections are caused by Staphylococcus aureus and Streptococcus pyogenes (Table 77–1). Rarely, infections in patients with burns, diabetes mellitus, or decubitus ulcers may involve gram-negative rods such as Pseudomonas or anaerobes. Hematogenous seeding of organisms into the skin can occur but is uncommon. Normal histology of the skin can be seen in Figure 77–1.

TABLE 77–1Skin and Skin Structures Infections: Appearance of Lesions, Skin Layers Involved, Common Pathogens, and Treatment Modalities
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TABLE 77–1 Skin and Skin Structures Infections: Appearance of Lesions, Skin Layers Involved, Common Pathogens, and Treatment Modalities
Type of Infection Appearance of Lesion Description of Lesion Layer of Skin Involved Common Pathogens Treatment
Impetigo

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 Vesicles with honey-colored crust, often on the face of a child Epidermis Staphylococcus aureus, Streptococcus pyogenes Few lesions: topical antibiotics (e.g., mupirocin); numerous lesions: systemic therapy (e.g., cephalexin, clindamycin)
Erysipelas

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 Erythematous, very painful lesion with sharply demarcated, raised, regular border Superficial dermis S. pyogenes, Streptococcus agalactiae > S. aureus Systemic antibiotics (e.g., cephalexin or cefazolin)
Cellulitis

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 Erythematous, diffuse, flat lesion with irregular border Deep dermis S. pyogenes, S. agalactiae > S. aureus Systemic antibiotics (e.g., cephalexin or cefazolin)
Folliculitis

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 Localized, inflamed papules containing a small amount of pus Hair follicle S. aureus, Pseudomonas aeruginosa (associated with hot tubs) Antibiotics often not needed; warm, moist compresses are useful
Skin abscess (also known as a boil, furuncle, carbuncle)

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 Raised, tender, inflamed nodule with central region of purulence; the area of pus initially is firm but then progresses to fluctuance (becomes movable) Deep dermis S. aureus Incision and drainage is mainstay of therapy; antibiotics directed against S. aureus in select cases
Necrotizing fasciitis

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 Very painful area of inflammation with rapid progression to necrosis, bullae, purpura, anesthesia, and systemic toxicity Fascia and muscle; local blood vessels and nerves also involved

Monomicrobial form: S. pyogenes, Clostridium perfringens, Vibrio vulnificus

Polymicrobial form: enteric gram-negative rods plus anaerobes

 Surgical debridement is critical in addition to broad-spectrum systemic antibiotics
FIGURE 77–1

Layers of the skin and subcutaneous tissue. Note sebaceous glands (purple coils) and hair follicles with protruding hair. (Reproduced with permission from Mescher AL. Junqueira’s Basic Histology: Text & Atlas. 13th ed. New York, NY: McGraw-Hill Education; 2013.)

A diagram depicts the layers and structures of the skin and subcutaneous tissue.
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A diagram depicts the layers and structures of the skin and subcutaneous tissue.

IMPETIGO

Definition

Impetigo is an infection of the epidermal layer of skin.

Pathophysiology

There are two modes of acquisition of impetigo, primary infection, which occurs in otherwise normal skin, or ...

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