What is the initial workup and treatment for a feline-associated infection?

Initial Workup and Treatment for Feline-Associated Infections

The initial workup for a feline-associated infection should include serologic testing for Bartonella henselae as the primary diagnostic method, followed by treatment with azithromycin (500 mg on day 1, then 250 mg for 4 additional days for patients ≥45.5 kg) as the first-line therapy. 1

Diagnostic Workup

History and Physical Examination

• Document history of cat exposure, especially:
  • Contact with kittens (<1 year old)
  • Cat scratches or bites
  • Flea infestation in cats
  • Timing of exposure
• Examine for:
  • Regional lymphadenopathy (most common presentation)
  • Inoculation site (may show papule or pustule)
  • Fever
  • Signs of disseminated disease in immunocompromised patients

Laboratory Testing

1. Serologic testing for Bartonella henselae antibodies (primary diagnostic method) 1
2. PCR testing of lymph node tissue specimens if available 1
3. Culture of blood, CSF, or lymph node specimens (though yield is low) 1
4. Basic laboratory workup:
   • Complete blood count
   • Comprehensive metabolic panel
   • Blood cultures if systemic symptoms present

Imaging

• Ultrasound or CT scan for suspected hepatosplenic involvement 2
• Consider imaging for patients with neurological symptoms or suspected osteomyelitis

Treatment Algorithm

Immunocompetent Patients with Typical Presentation

• First-line treatment: Azithromycin
  • Adults ≥45.5 kg: 500 mg on day 1, then 250 mg for 4 additional days
  • Children <45.5 kg: 10 mg/kg on day 1, then 5 mg/kg for 4 more days 1
• Many uncomplicated cases may resolve without antimicrobial therapy 3

Immunocompromised Patients

• Require longer treatment duration (2 weeks to 2 months)
• Options include:
  • Erythromycin 500 mg four times daily
  • Doxycycline 100 mg twice daily 1

Special Populations

• Pregnant patients: Erythromycin is recommended; avoid tetracyclines 1
• Diabetic patients: Consider amoxicillin-clavulanate 875/125 mg orally twice daily for 5-7 days, or doxycycline 100 mg twice daily for penicillin-allergic patients 1

Severe or Disseminated Disease

• Hospitalization may be required
• IV antibiotics should be considered
• Combination therapy may be necessary for severe infections 1

Follow-up and Monitoring

• Clinical reassessment within 24-48 hours for patients with lymphangitis and edema
• Follow-up appointment in 1-2 weeks to assess symptom resolution
• Inform patients that lymphadenopathy may persist for 1-6 months despite appropriate treatment 1

Prevention Strategies

• Implement flea control for cats
• Avoid rough play with cats
• Keep cats' nails trimmed
• Supervise children's interactions with cats
• Choose cats older than 1 year and in good health 1

Important Caveats

• Cat-scratch disease can present with atypical manifestations including Parinaud oculoglandular syndrome, neuroretinitis, persistent fever, hepatosplenic infection, encephalopathy, and osteomyelitis 3
• Immunocompromised patients are at risk for more severe disease including bacillary angiomatosis, bacillary peliosis, and relapsing bacteremia 3
• Cat and dog bites can lead to polymicrobial infections with organisms including Pasteurella, Streptococcus, Fusobacterium, and Capnocytophaga species 4
• Capnocytophaga canimorsus infection can cause severe sepsis, particularly in alcoholics and immunocompromised patients 5
• MRSA infections can be transmitted between pets and humans, particularly involving the USA300 clone 4