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

Objectives: Performance of the new Becton Dickinson ProbeTec GC Q ^x 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 Q ^x 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 Q^x assay; 13 were confirmed (PPV 50%; 95% CI 30% to 70%). Among 593 rectal samples, 17 tested positive by the ProbeTec GC Q^x assay; all were confirmed (PPV 100%; 95% CI 80% to 100%). Conclusions: The lower 95% CI of the PPV for the ProbeTec GC Q^x 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.