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1. SKIN & SOFT TISSUE INFECTIONS

ESSENTIALS OF DIAGNOSIS

  • Localized erythema with induration and purulent drainage.

  • Abscess formation.

  • Folliculitis commonly observed.

  • Gram stain of pus shows gram-positive cocci in clusters; cultures usually positive.

General Considerations

Approximately one-quarter of people are asymptomatic nasal carriers of S aureus, which is spread by direct contact. Carriage often precedes infection, which occurs as a consequence of disruption of the cutaneous barrier or impairment of host defenses. S aureus tends to cause more purulent skin infections than streptococci, and abscess formation is common. The prevalence of methicillin-resistant strains in many communities is high and should influence antibiotic choices when antimicrobial therapy is needed.

Clinical Findings

A. Symptoms and Signs

S aureus skin infections may begin around one or more hair follicles, causing folliculitis; may become localized to form boils (or furuncles [eFigure 33–6]); or may spread to adjacent skin and deeper subcutaneous tissue (ie, a carbuncle). Deep abscesses involving muscle or fascia may occur, often in association with a deep wound or other inoculation or injection (Figure 33–2)(eFigure 33–7). Necrotizing fasciitis, a rare form of S aureus skin and soft tissues infection, has been reported with community strains of methicillin-resistant S aureus.

eFigure 33–6.

Furuncle in a woman. (Used, with permission, from Richard P. Usatine, MD, in Usatine RP, Smith MA, Mayeaux EJ Jr, Chumley HS. The Color Atlas and Synopsis of Family Medicine, 3rd ed. McGraw-Hill, 2019.)

Figure 33–2.

Methicillin-resistant Staphylococcus aureus (MRSA) abscess on the back of the neck. (Used, with permission, from Richard P. Usatine, MD, in Usatine RP, Smith MA, Mayeaux EJ Jr, Chumley HS. The Color Atlas and Synopsis of Family Medicine, 3rd ed. McGraw-Hill, 2019.)

eFigure 33–7.

Large methicillin-resistant Staphylococcus aureus (MRSA) abscess on the leg in a 62-year-old man beginning to drain spontaneously. (Used, with permission, from Richard P. Usatine, MD, in Usatine RP, Smith MA, Mayeaux EJ Jr, Chumley HS. The Color Atlas and Synopsis of Family Medicine, 3rd ed. McGraw-Hill, 2019.)

B. Laboratory Findings

Cultures of the wound or abscess material will almost always yield the organism. In patients with systemic signs of infection, blood cultures should be obtained because of potential bacteremia, endocarditis, osteomyelitis, or metastatic seeding of other sites. Patients who are bacteremic should have blood cultures taken early during therapy to exclude persistent bacteremia, an indicator of severe or complicated infection.

Treatment

Proper drainage of abscess fluid or other focal infections is the mainstay of therapy. Incision and drainage alone ...

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