In vitro assessment of the APTIMA Combo 2 assay for the detection of Chlamydia trachomatis using highly purified elementary bodies

The Gen-Probe APTIMA Combo 2 assay has previously been reported to have a high sensitivity. The end point of this assay was evaluated using highly purified chlamydial elementary bodies (EBs). The performance of the APTIMA Combo 2 assay was compared with a commercially available PCR kit, AMPLICOR Chlamydia trachomatis. The number of inclusions of C. trachomatis at the end point of the APTIMA Combo 2 assay was 0.005 inclusion-forming units (i.f.u.) ml(-1), which was equivalent to 0.008 EBs per assay. The end point of the AMPLICOR kit was 5 i.f.u. ml(-1) (equivalent to 0.5 EB per assay). The efficacy of the AMPLICOR C. trachomatis assay was inhibited by phosphate or Fe2+ ion, while these had no effect on the APTIMA Combo 2 assay. In conclusion, the APTIMA Combo 2 assay appears to have a greater sensitivity than the AMPLICOR C. trachomatis assay for detection of C. trachomatis, while demonstrating few problems with inhibitory substances such as phosphate and Fe2+ ion.