Objective: To evaluate the performance of DNA amplification-based tests for the diagnosis of urethral chlamydia infection from the urine of asymptomatic young men.
Design: First-void urine was analyzed by two amplified DNA technologies, the ligase chain reaction (LCR), the polymerase chain reaction (PCR), and enzyme immunoassay (EIA). Specimens yielding discrepant results were subjected to retesting using either the original or a newly processed sample, and for evaluation of truly infected persons they were analyzed by the direct fluorescence antibody assay and by a second LCR directed against a segment of the gene encoding for the major outer membrane protein of Chlamydia trachomatis.
Setting: The military hospital in which military recruits underwent medical examination before departing for a United Nations mission.
Study group: Asymptomatic military recruits (705 young men) were screened between January and May 1994. In addition to providing urine specimens, the recruits completed questionnaires concerning previous genital infections and number of sexual partners.
Results: Overall prevalence of urethral chlamydia infection in the study group was 4.1% (29/705), as determined by confirmed results in all tests collectively. The performance of the DNA amplification methods was markedly better than that of the EIA antigen detection methods. Using an expanded gold standard, the sensitivity of the LCx assay was 93.1% (27/29) compared to 62.1% (18/29) by the PCR assay Amplicor and 37.9% (11/29) by EIA. Repeat testing after freezing and thawing increased the number of positive PCR results to equal the number of positive LCR results. There were three false-positive Amplicor results and no false-positive LCR results.
Conclusions: The LCx assay performed better than the Amplicor assay and appears reliable for urine testing. The low sensitivity of the Amplicor assay requires further evaluation of possible inhibitors of PCR in fresh specimens. It was found that freezing and thawing the specimens before testing enhanced the performance of PCR.