Pasteurella multocida

Snapshot

• A 40-year-old woman presents to the emergency room after being bitten by a cat. She had been visiting her boyfriend, who has 5 cats, when one of them was wary of strangers and bit her on the thumb. She cleaned it with some water and soap. On physical exam, she has a normal range of motion and sensation in her thumb. Her pulses are 2+ bilaterally. The wound is irrigated with sterile saline and wound is examined for any foreign bodies. She is started on empiric antibiotics to cover bacteria associated with cat bites.

Introduction

• Classification 
  • Pasteurella multocida
    • an facultative anaerobic gram-negative coccobacillus
    • encapsulated
    • can cause cellulitis at the site of inoculation
    • can also cause osteomyelitis
• Epidemiology
  • incidence
    • high in cat bites
  • demographics
    • male > female
    • more common in those < 20 years of age
  • risk factors
    • cat bites > dog bites
    • bites in the hand
    • deep penetrating wounds
    • immunosuppression
• Pathogenesis
  • direct inoculation of oral pathogens from animal bites into the wound, leading to infection
• cats have narrow and sharp teeth, which can inflict deep penetrating wounds with tiny wound openings that prevent good drainage

Presentation

• Symptoms
  • fevers
  • chills
• Physical exam
  • wound with signs of cellulitis
    • purulence
    • surrounding erythema
    • edema
  • osteomyelitis 
    • deep penetrating wound with bone involvement
• may have a foreign body in the wound

Imaging

• Radiography
  • indication
    • to rule out fracture
  • findings
    • fracture of bone
    • early signs of osteomyelitis
      • soft tissue swelling
      • focal bony lysis or cortical loss
• blurring of normal fat planes

Labs

• Labs
  • wound culture
  • blood cultures if a systemic infection is suspected
  • catalase positive
  • oxidase positive
  • grows on 5% sheep’s blood
• Making the diagnosis
• based on clinical presentation

Differential

• Tularemia 
  • distinguishing factors
    • associated with rabbits and ticks not with an animal bite
• presents with skin ulcer and lymphadenopathy

Treatment

• Management approach
  • wounds are not typically closed due to the risk of infection
• Conservative
  • wound care
    • indication
      • all patients
    • modalities
      • sterile saline irrigation
      • removal of any foreign bodies
• Medical
  • amoxicillin/clavulanate
    • indication
      • all patients
  • post-exposure prophylaxis
    • indication
      • patients with exposure risk
    • prophylaxis for
      • tetanus
• rabies

Complications

• Abscess
  • more common with cat bites