Objectives Nucleic acid amplification tests (NAATs) have rapidly replaced culture for the detection of Neisseria gonorrhoeae in many countries worldwide. Several commercial gonococcal NAATs have received US FDA clearance, including the APTIMA Combo 2 assay (AC2) and APTIMA GC assay (AGC) (Gen-Probe, San Diego, CA, USA). In this study, the analytical specificity and sensitivity of AC2 and AGC were evaluated on the Gen-Probe PANTHER instrument and specimens positive for N. gonorrhoeae using commercial diagnostic NAATs were verified by AGC.
Methods Samples spiked with 503 bacterial isolates (298 non-gonococcal Neisseria isolates and 205 gonococci) were tested. All initially equivocal and false-positive/false-negative results were verified according to a strict algorithm for confirmatory testing. Furthermore, 92 selected specimens tested positive for N. gonorrhoeae on Abbott RealTime PCR CT/NG (Abbott Laboratories) (n = 19), COBAS 4800 CT/NG (Roche Molecular Systems Inc.) (n = 34), or BD ProbeTec ET/Qx Chlamydia trachomatis and Neisseria gonorrhoeae Amplified DNA (Becton Dickinson) assays (n = 39) were examined for confirmation with AGC. For discrepancy analysis, a gonococcal diagnostic duplex PCR (targeting the porA pseudogene and opa genes) was used.
Results Both AC2 and AGC had 100% analytical specificity and sensitivity. Moreover, the verification of positive specimens from other commercial NAATs showed that all (100%; 19/19) specimens from Abbott RealTime PCR CT/NG, 94% (32/34) from COBAS 4800 CT/NG, and 51% (20/39) from BD ProbeTec ET/Qx Chlamydia trachomatis and Neisseria gonorrhoeae Amplified DNA could be verified as true positive in AGC (AGC results were confirmed in the gonococcal duplex PCR).
Conclusion The analytical specificity and sensitivity of AC2 and AGC were substantially challenged, and both assays displayed 100% specificity and sensitivity. This study also shows that AGC can be used for confirmatory testing as well as emphasises the importance of verifying particularly N. gonorrhoeae specimens that are low-positive or from extragenital sites with an alternative NAAT target.