Description

• Acute, spreading erythematous superficial infection of skin and SC tissues:
  • Nonpurulent SSTI (skin and soft tissue infection) = uncomplicated cellulitis
  • Purulent SSTI = cellulitis with purulent component is covered in “Abscess”
  • Extension into deeper tissues can result in necrotizing soft tissue infection
• Progressive spread of erythema, warmth, pain, and tenderness
• Predisposing factors:
  • Lymphedema
  • Tinea pedis or other toe web abnormalities
  • Open wounds
  • Pre-existing skin lesion (furuncle)
  • Prior trauma or surgery
  • Retained foreign body
  • Vascular or immune compromise
  • Injection drug use
  • Recurrent SSTI

Etiology

• Uncomplicated cellulitis (nonpurulent SSTI):
  • Group A streptococci
  • Methicillin-sensitive Staphylococcus aureus (MSSA)
  • Methicillin-resistant S. aureus (MRSA)
  • Risk factors for Staph infection (MSSA and MRSA):
    • Recent hospital or long-term care admission
    • Recent surgery
    • Children
    • Soldiers
    • Incarcerated persons
    • Athletes in contact sports
    • Injection drug use
    • Men who have sex with men
    • Dialysis treatments and catheters
    • History of penetrating trauma
  • Additional risk factors for MRSA infection:
    • Prior MRSA infection
    • MRSA colonization
    • Area of high MRSA incidence
    • Close contact with MRSA patient
• Extremity cellulitis after lymphatic disruption:
  • Nongroup A β-hemolytic streptococci (groups C, B, G)
• Cellulitis in diabetics:
  • Can be polymicrobial with S. aureus, streptococci, gram-negative bacteria, and anaerobes, especially when associated with skin ulcers
• Periorbital cellulitis:
  • Strep and Staph
• Buccal cellulitis:
  • Polymicrobial with anaerobic oral flora, associated with intraoral laceration or dental abscess
• Less common causes:
  • Clostridia
  • Anthrax
  • Pasteurella multocida – common after cat and dog bites
  • Eikenella corrodens – human bites
  • Pseudomonas aeruginosa:
    • Hot-tub folliculitis – self-limited
    • Foot puncture wound
    • Ecthyma gangrenosum in neutropenic patients
  • Erysipelothrix species – saltwater fish, poultry, meat, or hide handlers
  • Aeromonas hydrophila – freshwater swimming
  • Vibrio species – seawater or raw seafood

• Facial cellulitis in children:
  • Streptococcus pneumoniae
  • H. influenzae type B, although incidence significantly declining since introduction of HIB vaccine
• Perianal cellulitis:
  • Group A streptococci
  • Associated or antecedent pharyngitis or impetigo
• Neonates:
  • Group B streptococci