Chapter 133: Skin and Soft Tissue Infections

KEY CONCEPTS

• Folliculitis, furuncles (boils), and carbuncles begin around hair follicles and are caused most often by Staphylococcus aureus. Folliculitis and small furuncles are generally treated with warm, moist heat to promote drainage; larger furuncles and carbuncles require incision and drainage. Purulent, moderately severe infections (eg, with fever or other systemic signs of infection) have a higher suspicion for community-associated methicillin-resistant S. aureus (MRSA) and empiric treatment should include trimethoprim–sulfamethoxazole or a tetracycline such as doxycycline.

• Erysipelas, a superficial skin infection with extensive lymphatic involvement, is caused by Streptococcus pyogenes. The treatment of choice is penicillin, administered orally or parenterally, depending on the severity of the infection.

• Impetigo is a superficial skin infection that occurs most commonly in children. It is characterized by fluid-filled vesicles that rapidly develop into pus-filled blisters that rupture to form golden-yellow crusts. Effective therapy includes penicillinase-resistant penicillins (dicloxacillin), first-generation cephalosporins (cephalexin), and topical mupirocin or retapamulin. S. aureus is the primary cause of impetigo, with MRSA becoming more common in recent years.

• Lymphangitis, an infection of the subcutaneous lymphatic channels, is usually caused by S. pyogenes. Acute lymphangitis is characterized by the rapid development of fine, red, linear streaks extending from the initial infection site toward the regional lymph nodes, which are usually enlarged and tender. Penicillin is the drug of choice.

• Cellulitis is an infection of the epidermis, dermis, and superficial fascia most commonly caused by S. pyogenes and S. aureus. Lesions generally are hot, painful, and erythematous, with nonelevated, poorly defined margins. Oral trimethoprim–sulfamethoxazole, doxycycline, or minocycline is used for initial treatment of suspected MRSA in patients with purulent, moderately severe cellulitis (ie, lesion with purulent drainage or exudate, or nondrainable abscess plus systemic signs of infection). Treatment of nonpurulent cellulitis generally consists of penicillin VK, a penicillinase-resistant penicillin (dicloxacillin), first-generation cephalosporin (cephalexin), or clindamycin for 5 days; coverage for MRSA may be added in certain patients. More severe infections in hospitalized and/or immunocompromised patients should receive empiric therapy with parenteral agents active against streptococci (nonpurulent infections) or both streptococci and MRSA (purulent infections).

• Necrotizing fasciitis is an uncommon but life-threatening infection of subcutaneous tissue that results in progressive destruction of superficial fascia and subcutaneous fat. Early and aggressive surgical debridement is an essential part of therapy for treatment of necrotizing fasciitis. Mixed infections are treated with broad-spectrum regimens that cover streptococci, gram-negative aerobes, and anaerobes. Infections caused by S. pyogenes or Clostridium species should be treated with the combination of penicillin and clindamycin.

• Diabetic foot infections are managed with a comprehensive treatment approach that includes both proper wound care and antimicrobial therapy. Potential pathogens include staphylococci, streptococci, aerobic gram-negative bacilli, and obligate anaerobes. Antimicrobial regimens for diabetic foot infections are based on severity of the infection, expected ...