Chapter 73: Skin and Skin Structure Infections

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LEARNING OBJECTIVES

INTRODUCTION

Skin and skin structure infections (SSSIs), also known as acute bacterial skin and skin structure infections (ABSSIs), are frequently encountered in both acute and ambulatory care settings, with outpatient visits and hospitalizations increasing annually.¹ ABSSSIs range in severity from mild, superficial, and self-limiting, to life-threatening deep tissue infections requiring intensive care, surgical intervention, and intravenous (IV) broad-spectrum antibiotics. Gram-positive pathogens, primarily Staphylococcus aureus and Streptococcus species, are the most common causative bacteria.^2-5 Polymicrobial infections are more likely in complicated or deeper infections and in persons with immune suppression, diabetes, vascular insufficiency, or recent surgery.^2,5

The role of methicillin-resistant S. aureus (MRSA), particularly community-acquired methicillin-resistant S. aureus (CA-MRSA), in ABSSSI is of increasing importance. In many US cities, MRSA is the most frequently isolated pathogen from patients presenting to emergency departments with ABSSSI, and antimicrobial prescribing has largely shifted toward empiric use of MRSA-active agents.^3,6 Historically, MRSA infections were associated with health care exposure or defined populations such as injection drug users or athletes;^5,7 however, increasing MRSA prevalence in the community and its identification in otherwise healthy individuals means that risk stratification may be more difficult to perform. In areas with high rates of CA-MRSA, and in those with recurrent infections or infections that persist despite appropriate antimicrobial therapy, empiric therapy including antibiotics active against MRSA must be considered.^2,8 The general management of ABSSSIs is discussed throughout this chapter.

Intact skin generally is resistant to infection. In addition to providing a mechanical barrier, its relative dryness, slightly acidic pH, colonizing bacteria, frequent desquamation, and production of various antimicrobial defense chemicals, including sweat (which contains IgG and IgA), prevent invasion by various microorganisms.⁹ Conditions predisposing patients to ABSSSIs include: (a) high bacterial load (> 10⁵ microorganisms); (b) excessive skin moisture; (c) decreased skin perfusion; (d) availability of bacterial nutrients; and (e) damage to the corneal layer of the skin.¹⁰

IMPETIGO

EPIDEMIOLOGY AND ETIOLOGY

Impetigo is a common skin infection that can occur in any age group, but most frequently affects children between 2 and 5 years.¹¹ β-Hemolytic streptococci (Streptococcus pyogenes or Group A Streptococcus [GAS]) and S. aureus...