Positive predictive value of the Becton Dickinson VIPER system and the ProbeTec GC Qx assay, in extracted mode, for detection of Neisseria gonorrhoeae

Objectives Performance of the new Becton Dickinson ProbeTec GC Qx assay on the BD VIPER platform was evaluated to ascertain whether confirmatory testing is required in our clinical setting. Methods Positive predictive value (PPV) was determined by comparison with culture and a confirmatory nucleic acid amplification test (NAAT)-based Neisseria gonorrhoeae assay from genital and extragenital samples (rectal and pharyngeal) collected from a genitourinary medicine (GUM) clinic. Results Among 14 223 clinical genital samples, 149 (1.0%) specimens were positive using the ProbeTec GC Qx assay, automated on the VIPER platform; 141 of these were confirmed by either culture or a real-time PCR targeting two gonococcal-specific targets (PPV 94.6%; 95% CI 90% to 98%). Among 840 pharyngeal samples, 26 (3.1%) were positive by the ProbeTec GC Qx assay; 13 were confirmed (PPV 50%; 95% CI 30% to 70%). Among 593 rectal samples, 17 tested positive by the ProbeTec GC Qx assay; all were confirmed (PPV 100%; 95% CI 80% to 100%). Conclusions The lower 95% CI of the PPV for the ProbeTec GC Qx assay for genital specimens was >90% in this GUM clinic population, and therefore confirmatory testing for genital specimens is not required. Confirmatory testing of pharyngeal and rectal samples should continue in line with national guidelines.