False-Positive Enzyme Immunoassay Test Results for Chlamydia trachomatis Because of Contact of the Collection Swab With Agar

Abstract

We noted an increased incidence of false-positive Chlamydia trachomatis enzyme immunoassay results using the Abbott IMx SELECT C. trachomatis EIA test when a single swab was used for urethral sampling for both gonococcal culture inoculation and chlamydial detection. To evaluate if contact of the enzyme immunoassay collection swab with an agar produces false-positive chlamydial enzyme immunoassay results. Samples containing agar-based culture media were tested by two enzyme immunoassays and a ligase chain reaction technique. We report false-positive chlamydial enzyme immunoassay results using the Abbott IMx SELECT C. trachomatis EIA test if the collection swabs are in contact with gonococcal culture media (Modified New York City agar, chocolate, Thayer-Martin, or GC-lect) before insertion of the swab in the transport media of the enzyme immunoassay. The other assay results were negative. Using a single collection swab to screen for genital infections with gonococcal cultures and chlamydial enzyme immunoassay is inappropriate because it may lead to false-positive chlamydial enzyme immunoassay results, at least with the Abbott IMx SELECT C. trachomatis EIA test, incurring public health and financial consequences.