Upon completion of the chapter, the reader will be able to:
Discuss characteristics of the skin that render it resistant to infection.
Describe the epidemiology, etiology, pathogenesis, clinical manifestations, diagnostic criteria, and complications associated with skin and soft tissue infections (SSTIs).
Identify the desired therapeutic outcomes for patients with SSTIs.
Recommend appropriate empirical and definitive antimicrobial regimens when given a diagnosis, patient history, physical examination, and laboratory findings.
Monitor chosen antimicrobial therapy for safety and efficacy.
Skin and soft tissue infections (SSTIs) are frequently encountered in both acute and ambulatory care settings. They can range in severity from mild, superficial, and self-limiting, to life-threatening deep tissue infections that require intensive care, surgical intervention, and IV broad-spectrum antibiotics. Gram-positive pathogens, primarily Staphylococcus aureus and Streptococcus species, are the most common causative bacteria.1,2,3,4 Polymicrobial infections are more likely in complicated infections involving deeper layers of the skin, fascia, or muscle in persons with immune suppression, diabetes, and vascular insufficiency, and in postsurgical patients.1,4
The role of methicillin-resistant S. aureus (MRSA), particularly community-acquired methicillin-resistant S. aureus (CA-MRSA), in SSTI is of increasing importance. In many US cities, MRSA is the most frequently isolated pathogen from patients presenting to emergency departments with SSTI, and antimicrobial prescribing has largely shifted to empiric use of MRSA-active agents.2,5 MRSA infections were historically associated with exposures to health care settings and more defined populations such as injection drug users or athletes; however, the prevalence of MRSA in the community and its rise in otherwise healthy individuals means that historical high-risk groups have little clinical relevance in most areas. 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 this pathogen must be considered.1,6 This chapter covers the epidemiology, pathogenesis, clinical manifestations, and pharmacologic management of the more common and severe bacterial SSTIs.
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.7 Conditions that predispose a patient to SSTIs include: (a) high bacterial load (greater than 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.8
EPIDEMIOLOGY AND ETIOLOGY
KEY CONCEPT Impetigo is a common skin infection worldwide that can occur in any age group, but most frequently affects children between 2 and 5 years.9 β-Hemolytic streptococci and S. aureus are the most common causative pathogens.4 Impetigo is a superficial infection and spreads easily, ...