What is the recommended workup and treatment for cat scratch fever caused by Bartonella (Bartonellosis)?

Workup for Cat Scratch Fever (Bartonella henselae)

Diagnostic Approach

The diagnosis of cat scratch disease is primarily clinical, based on history of cat exposure (especially scratches or bites from kittens) and characteristic regional lymphadenopathy developing approximately 3 weeks after inoculation, with serologic testing reserved for atypical presentations or confirmation in difficult cases. 1, 2

Clinical Diagnosis

• Look for the classic triad: papule or pustule at inoculation site (developing 3-30 days post-scratch), regional lymphadenopathy (appearing ~3 weeks after exposure), and documented cat contact 1, 2
• The lymphadenopathy typically resolves spontaneously within 1-6 months, with suppuration occurring in only ~10% of cases 1, 2
• Extranodal disease is rare, occurring in ≤2% of cases 1, 2

When to Perform Laboratory Testing

Serologic testing is indicated when the clinical presentation is atypical, when extranodal disease is suspected, or when confirmation is needed for immunocompromised patients. 3

Serology (Primary Test)

• Immunofluorescent antibody (IFA) testing for B. henselae IgG antibodies with titers >1:256 supports the diagnosis 4
• Important caveat: antibodies may not be detectable until 6 weeks after acute infection in immunocompetent patients 3, 1
• In advanced HIV infection (CD4+ <100 cells/µL), up to 25% of culture-positive patients may never develop antibodies 3, 1
• Be aware of potential cross-reactivity between B. henselae and B. quintana 2

Tissue-Based Diagnosis (For Atypical Cases)

• PCR testing of lymph node tissue is valuable for atypical presentations or when serology is negative despite high clinical suspicion 1, 2
• Warthin-Starry silver stain of biopsied lymph node tissue demonstrates characteristic bacilli and vascular proliferation 3, 1
• Histopathology shows multiple microabscesses surrounded by histiocytes with plasma cell and lymphocyte infiltration 5
• Note: Tissue Gram stain and acid-fast stain are negative 3

Culture (Not Routinely Recommended)

• Blood or tissue culture is the gold standard but not practical due to the fastidious nature of Bartonella 3
• Culture is rarely performed in clinical practice and should not delay treatment 3

Special Populations Requiring More Aggressive Workup

Immunocompromised patients (especially those with CD4+ counts <100 cells/µL) require more thorough evaluation as they are at risk for disseminated disease including bacillary angiomatosis, peliosis hepatis, and CNS involvement. 3

• Consider Bartonella in any HIV patient with unexplained fever and CD4+ <100 cells/µL 3
• Evaluate for bacillary angiomatosis (cutaneous vascular lesions that can mimic Kaposi's sarcoma) 3
• Screen for hepatosplenic involvement and CNS disease in severely immunocompromised patients 3, 1

Testing NOT Recommended

• Do not test cats for Bartonella infection—this provides no benefit to diagnosis or management 3
• Routine culture or serologic testing of pets is not indicated 3

Key Diagnostic Pitfalls to Avoid

• Most cases in immunocompetent hosts are self-limited and do not require antibiotic treatment for resolution 6, 4
• Serology performed too early (<6 weeks) may yield false-negative results 3, 1
• In immunocompromised patients, absence of antibodies does not exclude infection 3, 1
• Bacillary angiomatosis lesions can be clinically indistinguishable from Kaposi's sarcoma—biopsy may be necessary 3