Comparison of cell culture with two direct Chlamydia tests using immunofluorescence or enzyme-linked immunosorbent assay.

Two direct tests for diagnosis of infection due to Chlamydia trachomatis were evaluated on 417 specimens collected from a population with a low disease prevalence of 8.1%. The intensity of positive results was graded according to the number of inclusions or elementary bodies and the optical density of the reaction. Thirty-four specimens were positive in cell culture, 39 positive with MicroTrak and 43 positive with Chlamydiazyme assay. The sensitivity of the two direct tests was 91.2% (31 of 34); the specificity was 97.9% (381 of 389) for MicroTrak and 96.9% (377 of 389) for Chlamydiazyme assay. The positive predictive values were 79.5% (31 of 39) for MicroTrak and 72.1% (31 of 43) for Chlamydiazyme assay. None of the specimens negative by the culture method were positive by the two direct methods. Discrepancies were restricted to the slightly positive specimens. The direct tests seem to be an alternative for diagnosing Chlamydia trachomatis infections, but slightly positive results require cell culture confirmation.