Currently, the indirect immunofluorescence assay(IFA) is used for detecting antibodies to Coxiella burnetii. Although reliable, this method is time-consuming, and the results are subject to interpretation. To develop an alternative test, we used
an
enzyme-linked immunosorbent asssy(ELISA) because it was faster, less complicated, and more objective than the IFA. The ELISA, unlike the IFA, cam also be automated.
In this study an indirect ELISA using C. burnetii protein antigens was developed to detect immunoglobulin G to C. burnetii phase I. A linear relation was found between the logarithms of absorbance values of sefa at a dilution of 1/300and the
titres
as
determined by and end point dilution ELISA. The finding of linear relation (r=0.95) confirmed that an ELISA value determined with a single serum dilution (1:300) can be interprete quantitatively as the titer of antibody in that serum.
A serum dilution of 1:300 was used in all subsequent teste at this dilution the differ ence between absorbance values for positive and negative sera was greatest:a serum sample was regarded as positive if the OD490 value was 0.185 (absorbance
threshold)
at this dilution. The results obtained by the ELISA were compared with those by the IFA established already.
The results indicate that the assay provides a sensitive, alternative method for diagnosing Q fever, but it needs reevaluation for the specificity because of its high false-positive rates.
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