In tests on 375 genital tract specimens a commercially available enzyme immunoassay for Chlamydia trachomatis (IDEIA; Boots-Celltech) was found to have sensitivity values of 62% for men and 74% for women, and a specificity of 97% for both groups, relative to the results obtained by a fluorescence assay (Micro Trak; Syva). The positive predictive value and the negative predictive value of the immunoassay were 91% and 87%, respectively. Collection of samples for IDEIA in transport medium in plastic phials, as opposed to glass phials recommended by the manufacturer, had no effect on these values. Tests of the sensitivity of IDEIA using laboratory strains of C trachomatis showed that the assay detected chlamydial elementary bodies only at dilutions at least 10-fold lower than those at which they could be detected by Micro Trak. Tests of the specificity of the assay with microorganisms found in the genital tract, other than chlamydiae, showed that reactions occurred with a number of these. Testing three cervical swabs from the same patient, with the material taken into a single phial of transport medium, increased the sensitivity of IDEIA from 74% to 96%, without reducing the specificity which remained at 97%. It is concluded that this approach enchances the value of the test in a sexually transmitted disease clinic population and may do so in a population with a low prevalence of chlamydiae.
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