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Skin and Soft Tissue Infection (SSTI) - VASP


See SSTI algorithm on VASP website


  • DDx: erysipelas, pyomyositis, necrotizing fasciitis, osteomyelitis, venous stasis, shingles, gout
  • Pathogens: Streptococcus species: Group A (most common), B, C, G, Staphylococcus aureus (including MSSA and MRSA)
    • Non-purulent, lymphangitis, or erysipelas? Think Streptococcus
    • Purulence (abscess or boil)? Think Staphylococcus
    • Strep anginosus is a strep species that can cause pus formation
  • 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 (Pseudomonas aeruginosa)
    • Immunocompromised: Fungal (Candida spp, Cryptococcus), Nocardia, non-tubercular mycobacteria)
    • Burn pts: Pseudomonas, Acinetobacter, Fusarium


  • 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
  • Blood cultures (BCx): ONLY needed if systemic signs of infection or immunocompromised (most pts will not need BCx or imaging)
  • US for underlying abscess
  • CT/MRI w/contrast: if necrotizing fasciitis, pyomyositis or osteomyelitis suspected
  • Bilateral lower extremity cellulitis is RARE and warrants consideration of non-infectious etiologies
  • Elevation test: if erythema improves after elevating leg above the level of the heart for 1-2 minutes, less likely to be infectious cellulitis


  • Abx for 5 days for uncomplicated; can extend to 10-14 days if little to no improvement, more extensive/serious infection, or if immunosuppressed
  • Typically improvement is not seen until >48 hours of antibiotics, usually longer
  • Provide anti-Staphylococcal antibiotics for purulent cellulitis in addition to I&D, if abscess present
  • Clinical appearance may often appear to worsen initially despite adequate therapy
  • Always elevate the extremity for more rapid clinical improvement!
No Staph suspected MSSA MRSA
Mild/Moderate (Outpt) Cephalexin 500 QID
Amoxicillin 500 TID
Cefadroxil 1g BID
Cephalexin 500 QID
Cefadroxil 1g BID
Dicloxacillin 500 QID
*Clindamycin 300-450 mg q6h
TMP/SMX 1-2 DS tabs BID
Doxycycline 100 mg BID
Severe (Inpt) Cefazolin 2g q8h
CTX 2g q24h
Cefazolin 2g q8h

PO step down: cephalexin 500 mg q6h or 1000mg q8h
Vancomycin (dose per PK)

PO step down: TMP/SMX 1-2 DS tabs BID
Doxycycline 100 mg BID
Linezolid 600 mg BID
Stepdown to PO options once:
- Staph aureus bacteremia is ruled out
- Clinical stability obtained >24 hours
- Patient is tolerating oral therapy
*Consider for PCN allergy; check antibiogram (VUMC vs VA) for Staph sensitivities; clindamycin should NOT be used for strep coverage

Necrotizing Fasciitis


  • Infection of the deeper soft tissues that causes necrosis along the muscle fascia and overlying subcutaneous 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


    • STAT consult to surgical service for emergent debridement (generally EGS vs ortho)
    • Imaging does NOT rule out necrotizing fasciitis and should not delay these consultations
    • CT is the best imaging modality
  • ID consult
  • Empiric antibiotics
    • Preferred: linezolid 600 mg IV BID + piperacillin-tazobactam 3.375g IV q8h extended infusion
    • For severe penicillin allergy: linezolid 600 mg IV BID + cefepime 2g IV q8h + metronidazole 500 mg IV BID
    • For severe penicillin and cephalosporin allergy: linezolid 600 mg IV BID + levofloxacin 750 mg IV q24h + metronidazole 500 mg IV BID
    • If patient cannot receive linezolid due to allergies, or multiple serotonergic drug interactions: vancomycin + piperacillin-tazobactam 3.375g IV q8h extended infusion + clindamycin 900mg IV q8h