Abstract: Impact of Chlamydia trachomatis Serovars on the Analytical Sensitivity of the GEN-PROBE® APTIMA Combo 2® Assay and New BD ProbeTec™ CTQx and GCQx Amplified DNA Assays* (2008 National STD Prevention Conference)

Wednesday, March 12, 2008

Continental Ballroom

Christine Welborn, MS , Molecular, Becton Dickinson, Sparks, MD

Tom L. Brink, MS , Molecular, Becton Dickinson, Sparks, MD

Amy Lloyd , Molecular, Becton Dickinson, Sparks, MD

Daryl Shank , Molecular, Becton Dickinson, Sparks, MD

William Lebar , Hospital Consolidated Laboratories - Providence Hospital, Southfield, MI

Background:
BD has developed two novel assays for detection of Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (GC) for use with the BD Viper™ System. Walk-away automation is achieved through the extraction of DNA from clinical specimens by binding to ferric oxide, followed by amplification and real-time fluorescent detection.

Objective:
To compare the analytical sensitivity of the BD ProbeTec™ Q^x and GEN-PROBE^® APTIMA Combo 2^® (AC2) assays using samples containing known concentrations of CT and GC and to investigate the impact on performance of two different CT serovars.

Method:
APTIMA^® Swab Transport Medium and Q^x Swab Diluent were co-spiked with CT and GC as follows: 15 Elementary Bodies and 25 cells/mL; 7.5 EB and 12 cells/mL. Separate panels were prepared using CT serovars LGV2 and H. Negative controls consisted of uninoculated medium. Panels were tested according to the manufacturers' instructions.

Result:
For both platforms all CT/GC-negative samples yielded negative results.
BD ProbeTec™ CTQ^x and GCQ^x Amplified DNA Assays
Positive Percent Agreement (PPA) with expected results for CT and GC was 100% for each organism and with both CT serovars.
AC2 Assay
PPA for GC was 100% in the presence of both CT serovars. In contrast, PPA for CT-LGV2 was 100% whereas PPA for serovar H at the same levels was 0%. Repeat testing of the serovar H panel with the alternative APTIMA^® CT Assay yielded 100% PPA.

Conclusion:
In contrast with the BD ProbeTec™ Q^x Assays and BD Viper™ System, the detection of CT by the GEN-PROBE^® AC2 Assay was shown to be serovar dependent.

Implications:
Under the conditions tested, the BD ProbeTec™ CTQ^x Assay was more analytically sensitive than the GEN-PROBE^® AC2 Assay for detection of CT serovar H. Further experiments are required to determine impact on clinical performance.
*BD ProbeTec™ Q^x Assays under development, not for sale or use

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