Evaluation of four nucleic acid amplification tests for Chlamydia trachomatis in urine specimens

Abstract number: P1155

Dean L., Perry K., Arnold E., Charlett A., Alexander S., Ison C., Underhill G., Lloyd A., Walker C., Mallinson H., Scragg S., Carder C., Ridgeway G.

Chlamydia trachomatis is the most common sexually transmitted infection in the United Kingdom and nucleic acid amplification testing (NAAT) is the method of choice for diagnosis. Our aim was to assess the diagnostic sensitivity and specificity of four commercially available NAATs: Roche COBAS AMPLICOR, BD ProbeTec ET, Gen-Probe Aptima 2 Combo and Artus C. trachomatis Plus real-time PCR. The tests were evaluated against the same specimen panel with the same reference standard using a statistically valid number of specimens to provide a confident measure of sensitivity and specificity.

The evaluation panel consisted of 2374 male and female urine specimens. Of these 1519 were negative and 595 were positive. Samples were assessed following the UK testing algorithm for C. trachomatis that demands retesting of all initially positive samples and defines a positive sample as one that is reproducibly positive by the test in use.

An imperfect standard was constructed using three of the four assays under evaluation (COBAS AMPLICOR, ProbeTec ET and Aptima 2 Combo). To help assess any resulting bias five different methods (denoted as options 1–5) were used to construct the standard, showing how much the sensitivity and specificity could vary. Sensitivity and specificity were assessed against the status defined by each of the options. The data below represents results from one of the five options used to define specimen status. Differences in sensitivity and specificity between each of the options were not statistically significant.

Overall, the most sensitive assay was the APTIMA 2 Combo (99.4%), followed by the COBAS AMPLICOR (96.85%), the ProbeTec ET (95.81%) and the Artus real-time PCR (94.9%). When data was analysed by sex, all assays were found to have a higher sensitivity with male urine specimens than with female urine specimens.

The ProbeTec ET assay had the greatest specificity (99.81%) followed by the COBAS AMPLICOR (98.17%), the APTIMA 2 Combo (98.15%) and the Artus real-time PCR (97.9%).

The assays evaluated achieved good sensitivity and specificity. However, we have demonstrated that there are statistically significant differences in the sensitivity of these assays. It is of note that the most sensitive test (APTIMA 2 Combo) was the least specific (99.37%) while the least sensitive (ProbeTec ET) was the most specific. This finding demonstrates the interrelationship between sensitivity and specificity inherent in all these test platforms.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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