Cellulitis is a topic covered in the 5-Minute Emergency Consult.

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  • Acute, spreading erythematous superficial infection of skin and SC tissues:
    • Variety of pathogens
    • Extension into deeper tissues can result in necrotizing soft tissue infection
  • Progressive spread of erythema, warmth, pain, and tenderness
  • Predisposing factors:
    • Lymphedema
    • Tinea pedis
    • Open wounds
    • Pre-existing skin lesion (furuncle)
    • Prior trauma or surgery
    • Retained foreign body
    • Vascular or immune compromise
    • Injection drug use


  • Simple cellulitis:
    • Group A streptococci
    • Staphylococcus aureus—including resistant strains such as community-associated methicillin-resistant S. aureus (CA-MRSA; see below):
      • CA-MRSA risk factors include: Prior MRSA infection, household contact of CA-MRSA patient, daycare contact of MRSA patients, children, soldiers, incarcerated persons, athletes in contact sports, IV drug users, men who have sex with men
      • Different antibiotic susceptibility than nosocomial MRSA
      • CA-MRSA now sufficiently prevalent to warrant empiric treatment
      • Suspect CA-MRSA in unresponsive infections
  • Nosocomial MRSA:
    • Risk factors: Recent hospital or long-term care admission, surgery, injection drug use, vascular catheter, dialysis, recent antibiotic use, unresponsive infection
    • Resistant to most antibiotics (see “Treatment”)
  • 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:
    • S. aureus
    • Streptococcal species
  • Buccal cellulitis:
    • Haemophilus influenzae type B
    • 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—raw fish, poultry, meat, or hide handlers
    • Aeromonas hydrophila—freshwater swimming
    • Vibrio species—seawater or raw seafood

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

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