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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); or may spread to adjacent skin and deeper subcutaneous tissue (ie, a carbuncle) (Figure 33–2). Deep abscesses involving muscle or fascia may occur, often in association with a deep wound or other inoculation or injection. Necrotizing fasciitis, a rare form of S aureus skin and soft tissues infection, has been reported with community strains of methicillin-resistant S aureus.

Figure 33–2.

Methicillin-resistant Staphylococcus aureus (MRSA) abscess of the neck. (From Edward Wright, MD; reproduced, with permission, from Usatine RP, Smith MA, Mayeaux EJ Jr, Chumley H, Tysinger J. The Color Atlas of Family Medicine. McGraw-Hill, 2009.)

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 is highly effective for the treatment of most uncomplicated cutaneous abscesses. A small benefit can be obtained from the addition of antimicrobials following incision and drainage. In areas where methicillin resistance among community S aureus isolates is high, recommended oral antimicrobial agents include clindamycin, 300 mg three times daily; trimethoprim-sulfamethoxazole, given in two divided doses based on 5–10 mg/kg/day of the trimethoprim component; or doxycycline or minocycline, 100 mg twice daily. When the risk of methicillin resistance is low or methicillin susceptibility has been confirmed by testing of the isolate, consider dicloxacillin or cephalexin, 500 mg four times a day (see Table 33–1). Seven days of treatment are sufficient in most cases.

For complicated infections with extensive cutaneous or deep tissue involvement or fever, ...

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