Skin and Soft Tissue Infection (STI)

Matthew Melton

Cellulitis

See SSTI algorithm on VASP website (https://www.vumc.org/antimicrobial-stewardshipprogram/ guidelines)

Background 

  • PurulentSSTIs: abscesses, furuncles, carbuncles. Predominantly S. aureus 
  • NonpurulentSSTIs: cellulitis, erysipelas. Predominantly β-hemolytic streptococci>>MRSA 
  • Necrotizingfasciitis: severe pain disproportionate to exam, wooden-hard induration, crepitus, bullae, skin necrosis, systemic toxicity. Monomicrobial (S. pyogenes, MRSA, V. vulnificus, A. hydrophila) or polymicrobial (mixed aerobe-anaerobe) 
  • Pyomyositis: S. aureus>Strep>GNRs 
  • Entry via skin disruption; risk factors include edema, lymphedema, venous insufficiency, obesity, DM, and immunosuppression 
  • Unique clinical scenarios and associated organisms/organisms to consider: 
    • Dog/cat bite: Pasteurella multicoda, Capnocytophaga canimorsus 
    • Human bite: Eikenella corrodens, oral anaerobes, S. aureus 
    • Fresh water exposure: Aeromonas hydropholia, Plesiomonas shigelloides 
    • Salt water exposure: Vibrio vulnificus 
    • Neutropenia, presence of ecthyma: Gram negatives (PsA) 
    • Immunocompromised: Fungal (Candida spp, Cryptococcus), Nocardia, non-tubercular mycobacteria) 
    • Burn pts: PsA, Acinetobacter, Fusarium 
  • DDx: erysipelas, pyomyositis, necrotizing fasciitis, osteomyelitis, venous stasis, shingles, gout

Evaluation 

  • Outline border of erythema and obtain urgent surgery consultation if rapid spread of infection, crepitus, air in tissues, or pain out of proportion to exam 
  • BCx ONLY needed if systemic signs or immunocompromised 
  • US for underlying abscess. CT/MRI w contrast: if nec fasc, pyomyositis or osteo suspected 
  • Elevation test: if erythema improves after elevating leg above the level of the heart for 1-2 minutes, less likely to be infectious cellulitis

Management 

Vandy ASP Guidance Document for Inpatient SSTI

  • Purulent cellulitis: Staph; Tx 5d 
  • <1 SIRS Empiric: TMPSMX, Cephalexi n+Doxy, Cefadroxil, Linezolid 
  • >1 SIRS Empiric: Vanc+CTX or Vanc+Amp- Sulbactam 
  • Cutaneous Abscess, Furuncle, Carbuncle: Staph 
  • I&D wo abx unless: >1 SIRS criteria, >2 cm erythema, multiple abscesses, incomplete I&D or lack of response, immunocompro mised, then Cx purulence and 5d tailored abx 
  • Pyomyositis: Staph; Tx 14-21d 
  • Empiric: Vanc+CTX, narrow based on BCx and abscess Cx QR: Vandy ASP Guidance Document for Inpatient SSTI:
  • Erysipelas/Cellulitis: Strep>Staph; Duration 5d 
  • <1 SIRS: Cephalexin/Cefazolin, Cefadroxil; TMP-SMX or linezolid if MRSA risk factors (IVDU, penetrating trauma) 
  • >1 SIRS: CTX, Vanc if MRSA risk factors 
  • Impetigo: Staph, Strep; Tx 5d 
  • Single Lesion: Mupirocin 2% ointment 
  • Multiple Lesions: Amox-clav, cephalexin, cefadroxil 
  • Bites: Varies by animal, see ASP guidance document for species-specific recs

Necrotizing Fasciitis

Background 

  • Infection of the deeper soft tissues causing necrosis along the muscle fascia and overlying subQ fat that is rapidly progressive and lethal if not addressed
  • Clinical cues include rapid spread, pain out of proportion to exam, crepitus and hemorrhagic bullae
  • LRINEC score used to screen for necrotizing soft tissue infection

Evaluation/Management 

  • SURGICAL EMERGENCY-STAT consult to surgical service for emergent debridement (generally EGS vs ortho)
  • ID consult
  • Empiric abx 
    • Preferred: linezolid+pip-tazo 
    • For severe PCN allergy: linezolid+cefepime+metro 
    • For severe PCN and cephalosporin allergy: meropenem + linezolid 
    • If patient cannot receive linezolid (allergies, serotonergic DDI): vanc+pip-tazo+clinda
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