Laboratory diagnosis of Chlamydia trachomatis using two immunodiagnostic methods

Seven hundred seventy-seven endocervical specimens collected from symptomatic and asymptomatic women in a low-prevalence population were examined for the presence of Chlamydia trachomatis by both enzyme immunoassay (EIA) and by direct immunofluorescence assay (DFA). Overall, 49 (6.2%) of specimens had positive results, however, only 26 had positive results by both assays. Concordant positivity was significantly higher in specimens from symptomatic women not taking antibiotics as compared with all other groups. Test discordance was not influenced by order of specimen collection, number of days of delay before the specimen was processed by EIA, cervical cytologic results, amount of mucopurulence, or presence of a particular bacterial species in simultaneously collected cervical swabs. The EIA optical density (OD) reading appeared to discriminate between the different test result groups more reliably than the number of elementary bodies seen on the DFA slide. Specimens with an OD reading greater than 0.300 and less than 0.060 can be interpreted with assurance as positive and negative, respectively. Caution may be necessary with specimens with intermediate values.