Vaccination against Q Fever (Coxiella burnetii infection) is performed in Australia using Q-VAX, a formalin-killed whole cell vaccine. Adverse reactions occur in those persons with prior exposure to C.burnetii. To prevent this adverse reaction pre-vaccination screening is performed and persons found to be positive are excluded from vaccination. Currently a skin test (to detect T-cell immunity) and an antibody assay (to detect B-cell immunity) are undertaken on each person prior to vaccination. However the assay that "best" correlates with prior exposure to C.burnetii and thus adverse reactions to the vaccine is not known.
A new interferon-gamma release assay (IGRS), "Q-Detect", has recently become available. This new assay and 4 current assays were compared.
A small group (n=25) of attendees at an Australian scientific conference were offered Q-VAX vaccination. As part of their pre-vaccination testing, 5 different assays were performed on them to detect their possible prior exposure to C.burnetii. The assays were:
Of the 25 participants in the study, 7 had prior exposure to C.burnetii due to vaccination against Q Fever and 1 had prior Q Fever infection. The remaining 17 persons had no known prior exposure to C.burnetii.
The results from the 5 assays were compared in the 2 groups and the sensitivity and specificity of the assays calculated, as under:
Assay Sensitivity Specificity Conclusion
1 skin test 37% 76% Poor
2 serology IF 62% 100% Poor
3 serology EIA 25% 100% Poor
4 serology CFT 12% 100% Poor
5 IGRA 100% 82% Good
The new IGRA "Q-Detect" is superior to the 4 currently used assays for detecting prior exposure to C.burnetii in persons seeking vaccination against Q Fever in Australia.