Confirmation of the Syva Micro Trak Enzyme Immunoassay for Chlamydia trachomatis by Syva Direct Fluorescent Antibody Test

Background and Objectives: The Syva MicroTrak enzyme immunoassay (EIA) is used widely for screening women infected with Chlamydia trachomatis. Confirmatory tests used in conjunction with EIA screening have shown that false-positive results are common. Goals: To evaluate the specificity of the Syva MicroTrak EIA by confirmation of positive specimens with the Syva Direct Fluorescent Specimen Test. Study Design: Of 6,039 endocervical specimens collected from women attending Colorado family planning clinics, 328 positive EIA results (5.4%) were obtained by Syva MicroTrak EIA. A random subset of 136 positive specimens was tested by Syva Direct Specimen Test. Twenty of 136 specimens (14.7%) negative by Syva Direct Specimen testing were also tested by Syva blocking antibody tests (9 of 20 positive, 45%) and Roche Amplicor polymerase chain reaction (PCR; 6 of 20 positive, 30%). Of 20 specimens positive by Syva MicroTrak EIA and negative by Syva Direct Specimen Test, 11 (55%) were also negative by blocking antibody and PCR, including three specimens with initial EIA sample-to-cutoff ratios greater than 2. Conclusions: Confirmatory testing of Syva MicroTrak EIA positive specimens with Syva Direct Specimen Test showed that 14.7% were false positive. Coupling the Syva Direct Specimen test with either blocking antibody or PCR reduces the rate of false-positive results to 8%.