Q Fever Antibody
Overview
Q fever antibody measures serologic response to Coxiella burnetii antigens, primarily phase I and phase II IgG and IgM, indicating past or current infection with this obligate intracellular bacterium. These antibodies reflect immune recognition of the pathogen responsible for acute fever, pneumonia, or chronic endocarditis. Elevated phase II IgM/IgG suggests acute infection, while high phase I IgG titers indicate chronic disease like endocarditis; the test is clinically useful for diagnosing Q fever across its diverse presentations, guiding antibiotic therapy, and conducting epidemiological surveillance.
Clinical Use Cases
- Diagnosing acute Q fever (pneumonia, hepatitis, fever of unknown origin).
- Identifying chronic Q fever endocarditis or vascular infections.
- Differentiating acute from chronic infection via phase I/II titer ratios.
- Screening livestock workers or outbreak investigations.
- Monitoring treatment response in endocarditis cases.
Specimen Types
- Serum (primary).
- Plasma (less common).
Measurement Methods
- Indirect immunofluorescence assay (IFA, reference standard).
- Enzyme-linked immunosorbent assay (ELISA).
- Complement fixation test (historical).
- Immunoblot (confirmatory).
Test Preparation and Influencing Factors
- No fasting required.
- Acute and convalescent sera (2-3 weeks apart) improve diagnostic accuracy.
- Recent antibiotics (doxycycline) may blunt antibody response.
- Cross-reactivity possible with Legionella or Chlamydia.
- Timing critical: IgM peaks 2-3 weeks post-infection.
Synonyms
- Coxiella burnetii serology.
- Phase I/II antibodies.
- C. burnetii IgG/IgM.