Necrotizing Fasciitis and Other Soft Tissue Infections
Stewart R. Carter
David H. Ahrenholz
Fred A. Luchette
I. OVERVIEW
A. General principles.
1. Our skin functions as a barrier to infection; therefore, any break in the skin can allow bacteria to invade.
2. Risk factors for infection include trauma, edema, hematoma, ischemia, and foreign body.
3. Virulent infections are associated with impaired host defenses (i.e., diabetes, cancer, malnutrition, immunosuppression, advanced age, and major trauma).
B. Pathophysiology.
1. Group A, β-hemolytic Streptococcus pyogenes: highly virulent; cellulitis; erysipelas with demarcated borders; ecthyma contagiosum; streptococcal lymphangitis; seen in necrotizing fasciitis; exotoxins result in lymphocyte activation causing shock (toxic shock syndrome [TSS]) (see Sections II and III).
2. Staphylococcus aureus: most common cause of skin infection; purulence; folliculitis (dermis); superficial abscess (soft tissue); carbuncle (burrowing infection); pyomyositis (hematogenous spread to intramuscular hematoma); also associated with necrotizing fasciitis. Also produces TSS (see Sections II and IV). A growing number of skin and soft tissue infections (SSTIs) are the result of methicillin-resistant Staphylococcus aureus (MRSA) infection.
3. Clostridium perfringens, Clostridium novyi, Clostridium septicum, and Clostridium tertium: most common in ischemic muscle; exotoxins cause myonecrosis and sepsis (see Section V).
4. Eikenella corrodens: human bite wounds; sensitive to cephalosporins and penicillin.
5. Pasteurella multocida: animal bites or scratches; treat with cephalosporins, penicillin, tetracycline, trimethoprim-sulfamethoxazole + clindamycin.
6. Vibrio vulnificus: aggressive disease; more common in alcoholics; due to immunologic defects; marine-related organisms; aggressive debridement and treat with doxycycline plus intravenous ceftazidime. Ciprofloxacin is alternative (see Section III).
7. Escherichia coli, Klebsiella: abscess of perineal area; usually arising from infected pilonidal cyst or laceration of rectal mucosa causing a perirectal abscess; can occur in other areas; initially treat with drainage and fluoro-quinolones when indicated.
8. Cryptococcus neoformans and other fungi can mimic cellulitis due to group A Streptococcus (see Section II).
9. Bartonella: Gram-negative bacteria previously classified as rickettsiae; cause several uncommon diseases: cat-scratch disease, an acute febrile anemia, a chronic cutaneous eruption, and disseminated disease in immunocompromised hosts; treat with gentamicin and a second antibiotic depending on the Bartonella species and severity of the disease process.
10. Actinomycosis: chronic localized or hematogenous infection due to Actinomyces israelii; local abscess with multiple draining sinuses; seen more commonly in adult males as cervicofacial (lumpy jaw) abscess, portal of entry is decayed teeth; treat with surgical excision followed by cephalosporins.
II. CELLULITIS AND SUBCUTANEOUS INFECTIONS
A. Etiology.
1. Most common organisms: S. aureus and group A streptococci causing a diffuse cutaneous infection; nonpyogenic; starts with a minor break in skin, such as an insect bite, puncture limited to skin, and subcutaneous tissues; infections spread through tissue facilitated by toxins and enzymes.
2. In the extremity: presents with lymphadenitis or lymphangitis involving dermal lymphatics.
3. High-risk cellulitis when infection involves the face or extremities of immunocompromised patients.
4. Folliculitis: nontoxic pyodermas centered in hair follicles.
5. Subcutaneous abscess (complicated cellulitis): most common soft tissue infection.
6. Hidradenitis suppurativa: chronic burrowing infection of groin or axilla involving infected hair follicles; more commonly seen in diabetic or very obese patients.
7. Community-acquired MRSA: because of increasing cases of MRSA soft tissue infections, the distinction between community-acquired, and health care-associated MRSA is becoming less useful in guiding therapy.
B. Diagnosis.
1. Presents with progressive erythema and edema; may cause tenderness over the involved area.
2. Varying diagnostic yield on cultures of tissue or aspirate; due to the emergence of MRSA, routine culture is important for guiding antimicrobial susceptibility.
C. Treatment.
1. Uncomplicated cellulitis: treatment with antibiotics and elevation; surgery not indicated unless joints or tendon sheath are involved.
2. β-lactams (penicillins, nafcillin, cephalosporins, carbapenams), or if concern for MRSA; clindamycin, trimethoprim-sulfamethoxazole, doxycycline, minocycline, or linezolid.
3. Abscess, furuncle, or carbuncle all require incision and drainage.
