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Q fever serology: cutoff determination for microimmunofluorescence
H T Dupont1, X Thirion, D Raoult
1Unité des Rickettsies, CNRS EP J 0054, Marseille, France.
Clinical and Diagnostic Laboratory Immunology
|March 1, 1994
Summary
New Q fever diagnostic cutoffs are established for immunoglobulin G (IgG), IgM, and IgA antibodies against Coxiella burnetii. These updated serological criteria improve the accuracy of diagnosing both acute and chronic Q fever.
Area of Science:
- Medical Microbiology
- Infectious Diseases
- Immunoserology
Background:
- Q fever, a zoonosis caused by Coxiella burnetii, presents with varied clinical symptoms, necessitating reliable serological diagnosis.
- Current diagnostic cutoff titers for Q fever lack validation from extensive patient cohorts.
- Accurate differentiation between acute and chronic Q fever is crucial for effective treatment.
Purpose of the Study:
- To determine updated serological cutoff titers for diagnosing acute and chronic Q fever.
- To evaluate the diagnostic utility of immunoglobulin G (IgG), IgM, and IgA antibodies against Coxiella burnetii phases I and II.
- To assess the kinetics of antibody development in Q fever patients.
Main Methods:
- Analysis of 2,218 first serum samples from patients with suspected Q fever, including those with confirmed acute (208) and chronic (53) cases.
- Quantification of IgG, IgM, and IgA antibody titers against Coxiella burnetii phases I and II using microimmunofluorescence.
- Removal of rheumatoid factor prior to IgM and IgA testing to enhance specificity.
Main Results:
- For active Q fever, a low cutoff (phase II IgG titer ≤100) requires further confirmation, while a high cutoff (phase II IgG titer ≥200 and phase II IgM titer ≥50) confirms the diagnosis.
- Phase I IgA titers are not significantly contributory for chronic Q fever diagnosis.
- A phase I IgG titer ≥800 is highly predictive (98%) and sensitive (100%) for chronic Q fever.
- Phase II IgG and IgA titers can suggest or exclude chronic Q fever when phase I testing is unavailable, albeit with lower sensitivity (57%).
Conclusions:
- Updated serological cutoff titers for IgG, IgM, and IgA antibodies provide more reliable Q fever diagnosis.
- The established criteria enhance the accuracy of differentiating between acute and chronic Q fever.
- The findings refine diagnostic strategies for Q fever, particularly when phase I antigen testing is limited.