Cellulitis

• Infection of superficial skin and skin structures

Etiology

• Streptococcus pyogenes (much more common)
• Staphylococcus aureus (especially if purulent)
• Rare, depending on exposures:
  • Hand or foot puncture: Pseudomonas aeruginosa
  • Facial cellulitis in children: Haemophilus influenzae
  • Human bite wounds: Anaerobes, Eikenella, viridans-group Streptococci
  • Cat or dog bites: Pasteurella multocida
  • Saltwater exposure: Vibrio vulnificus (e.g. injury on coral)
  • Fresh- or saltwater exposure: Aeromonas hydrophila (e.g. leech bites)
  • Butchers: Erysipelothrix (erysipeloid)

Differential Diagnosis

• Skin and soft tissue infections
  • Cellulitis (Strep/Staph)
  • Erysipelas (usually Strep)
  • Abscess (usually Staph)
  • Folliculitis (usually Staph or Pseudomonas): warm compresses and mupirocin ointment
  • Impetigo (usually Staph): watchful waiting, or topical or systemic antibiotics
  • Carbuncles
  • Necrotizing fasciitis
• Other disease
  • Deep vein thrombosis
  • Gout (if over a joint)
  • Erythema nodosum
• For an exhaustive list, see [Cellulitis mimickers](Cellulitis mimickers.md)

Presentation

• Hot, red, swollen, tender area of skin with poorly demarcated margins
• With or without pus and/or bullae
• Legs more common than elsewhere

Management

• Source control: drain any abscess
• Antibiotics for 5-7 days
• Purulent SSTI
  • Cephalexin or cefazolin are good first-line empiric choices
  • Doxycycline or vancomycin can also be considered
• Non-purulent SSTI
  • Cephalexin 500mg po qid or cefazolin 1-2g IV q8h for 5-7 days
  • If penicillin allergy
    • Clindamycin300mg po qid
    • Moxifloxacin 400mg po daily
    • Linezolid 600mg po bid
    • Clindamycin 600mg IV tid
    • Vancomycin 1g IV q12h
• Non-resolving cellulitis
  • Bug-drug mismatch
  • Resistance
  • Poor antibiotic choice
  • Unusual organism
    • Water exposure (fresh- or saltwater)
    • Fish
    • Shellfish, meats, hides
    • IV drug use
    • Animal or human bites
  • Poor adherence/absorption/distribution
  • Wrong diagnosis
  • Impatience!
• Complications of infection
  • Abscess (drain it)
  • Deep infection
  • Metastasis

Prophylaxis

• May be indicated for patients with recurrent cellulitis
• Penicillin V 250 mg po bid
• Read more: Oh CC et al. Antibiotic prophylaxis for preventing recurrent cellulitis: A systematic review and meta-analysis. J Infect. 2014;69(1):26-34.