Can a dog scratch cause cellulitis?

Dog Scratches Can Cause Cellulitis

Yes, dog scratches can cause cellulitis, particularly when the scratch breaks the skin and introduces bacteria such as Pasteurella multocida, which can lead to rapidly developing infection within 24-72 hours after injury. 1

Pathophysiology and Causative Organisms

Dog scratches create breaks in the skin barrier that allow bacteria to enter the deeper tissue layers. While cellulitis is most commonly caused by streptococci or Staphylococcus aureus, animal-associated cellulitis often involves different pathogens:

• Pasteurella multocida - The predominant organism in dog and cat scratch/bite infections 1, 2
• Capnocytophaga canimorsus - Another potential pathogen from dog scratches 1
• Staphylococcus and Streptococcus species - May be present as co-infecting organisms

Clinical Presentation

Cellulitis from dog scratches typically presents with:

• Rapid onset of symptoms (often within 12-24 hours) 2
• Localized erythema, edema, warmth, and tenderness at the scratch site
• Serosanguineous or purulent drainage
• Possible lymphangitis (red streaking)
• Systemic symptoms may include fever and malaise

The speed of symptom onset is a key distinguishing feature of animal-associated cellulitis, particularly with Pasteurella infections, which can progress much faster than typical cellulitis cases 2, 3.

Diagnosis

Diagnosis is primarily clinical, based on:

• History of dog scratch or bite
• Characteristic appearance of rapidly developing cellulitis
• Timing of symptom onset (12-24 hours after injury is typical for Pasteurella)

Blood cultures are generally unnecessary for typical cases but should be considered for patients with:

• Severe systemic features
• Immunocompromised status
• Unusual predisposing factors 1

Treatment

First-line Treatment:

• Penicillin or amoxicillin is the treatment of choice for Pasteurella infections 2, 3

Alternative Options:

• Amoxicillin-clavulanate for broader coverage
• Doxycycline or fluoroquinolones for penicillin-allergic patients
• Clindamycin (note: may have less activity against Pasteurella)

Severe Infections:

• Hospitalization with intravenous antibiotics
• Surgical debridement may be necessary for necrotizing infections 4

Prevention and Risk Reduction

To prevent cellulitis from dog scratches:

• Immediately clean all scratches with soap and water
• Apply antiseptic solution
• Monitor for early signs of infection
• Seek medical attention promptly if redness, swelling, or pain develops

Special Considerations

• Immunocompromised patients are at higher risk for severe infections and complications
• Location matters - hand injuries are particularly prone to complications due to complex anatomy 2
• Timing is critical - treatment delay can lead to deeper tissue involvement, including necrotizing fasciitis in severe cases 4

Common Pitfalls

1. Delayed treatment - Pasteurella infections progress rapidly and require prompt antibiotic therapy
2. Inadequate antibiotic selection - Using antibiotics without activity against Pasteurella
3. Failure to recognize severity - Animal-associated cellulitis can progress to deeper tissue infection more rapidly than typical cellulitis
4. Overlooking the diagnosis - Not connecting the dog scratch history to the presenting cellulitis

Remember that while typical cellulitis is most commonly caused by streptococci and staphylococci, the presence of an animal scratch or bite should raise suspicion for other pathogens, particularly Pasteurella multocida, which requires specific antibiotic coverage.