What should the initial diagnosis (dx) be for a dog bite?

Initial Diagnosis and Management of Dog Bite Wounds

The initial diagnosis for a dog bite should be "animal bite wound infection" with specific consideration for Pasteurella species, which are isolated from 50% of dog bite wounds, along with staphylococci and streptococci found in approximately 40% of cases. 1

Microbiology and Pathogen Considerations

Dog bite wounds are often polymicrobial in nature, containing:

• Pasteurella canis (in 50% of dog bites) 1
• Staphylococcus species 1
• Streptococcus species 1
• Moraxella species 1
• Saprophytic Neisseria species 1
• Various anaerobes 1
• Capnocytophaga canimorsus (particularly concerning in asplenic or hepatic disease patients) 1

Initial Assessment

When evaluating a dog bite wound, assess for:

• Time since injury (infections typically develop after 8-12 hours) 1
• Wound characteristics:
  • Non-purulent (30% of dog bites)
  • Purulent (58% of dog bites)
  • Abscess formation (12% of dog bites) 1
• Signs of deeper infection (pain disproportionate to injury near bone/joint suggests periosteal penetration) 1
• Hand wounds (require special attention as they're often more serious) 1

Specimen Collection

If infection is suspected:

• Collect tissue or aspirate specimens rather than swabs when possible 1
• Ensure proper anaerobic transport conditions 1
• Perform Gram stain to assess for inflammation indicators and microorganisms 1
• Consider blood cultures if systemic disease is suspected 1

Treatment Approach

Wound Management

1. Clean wound with sterile normal saline (no need for iodine or antibiotic solutions) 1
2. Remove superficial debris 1
3. Consider primary closure after proper cleaning unless the wound is:
   • Located on the hand
   • Heavily contaminated
   • Presented >8 hours after injury 2

Antimicrobial Therapy

For outpatient treatment:

• First-line: Amoxicillin-clavulanate 1, 3, 2

Alternative options:

• Doxycycline (for patients ≥8 years old) 3
• Combination therapy with penicillin VK plus dicloxacillin 1

For inpatient treatment:

• β-lactam/β-lactamase combinations (ampicillin-sulbactam)
• Piperacillin-tazobactam
• Second-generation cephalosporins (cefoxitin)
• Carbapenems (ertapenem, imipenem, meropenem) 1

Antibiotics to Avoid

• First-generation cephalosporins (cephalexin)
• Penicillinase-resistant penicillins (dicloxacillin)
• Macrolides (erythromycin)
• Clindamycin alone 1

These antibiotics have poor activity against Pasteurella multocida and should be avoided for dog bites.

Special Considerations

• Duration of therapy: Standard 5-7 days for uncomplicated infections 3
• Extended therapy needed for complications:
  • Osteomyelitis (4-6 weeks)
  • Synovitis (3-4 weeks) 1
• Tetanus prophylaxis: Evaluate need based on immunization status 2
• Rabies post-exposure prophylaxis: Consider based on circumstances of the bite 2

Potential Complications

• Septic arthritis
• Osteomyelitis
• Subcutaneous abscess formation
• Tendonitis
• Bacteremia (rare) 1
• Non-infectious complications: nerve/tendon injury, compartment syndromes, post-traumatic arthritis 1

Clinical Pearls

• Wounds should be reassessed within 72 hours of starting therapy 3
• Hand wounds require special attention due to higher risk of complications 1
• Pain disproportionate to injury near a bone or joint suggests deeper infection 1
• Surgical drainage is essential if an abscess develops 3

Remember that dog bites account for approximately 337,000 emergency visits annually in the United States, with medical costs reaching up to $2 billion per year 2. Proper initial diagnosis and prompt treatment are essential for preventing complications and ensuring optimal outcomes.