Evaluation of a direct fluorescence assay as a screening method in asymptomatic young women

The purpose of the study was to evaluate one rapid antigen test (DFA), in comparison to culture, for the detection of Chlamydia trachomatis in young, asymptomatic women. C. trachomatis was isolated from specimens of 8.6% of the patients studied, and 11.3% had 10 or more elementary bodies (EBs) in their specimens. A lowered cut-off point of the DFA did not affect the sensitivity of the method, but the predictive value of a positive test decreased markedly when the cut-off point was lowered. Patients with symptoms of genital infection, signs of genital infection, or both had a higher DFA sensitivity than those who were asymptomatic. Patients whose specimens yielded 1-9 EBs were reexamined three times, once every fourth week. We found little evidence that those patients should be regarded as falsely negative in culture, since most of them remained negative. In order to minimize the social consequences of a false positive test, the DFA method should not be substituted for culture as a diagnostic tool, especially for screening of asymptomatic groups with a low prevalence of C. trachomatis.