Performance of the BD ProbeTecTM Qx Amplified DNA Assay on the BD ViperTM System with XTRTM Technology for Non-Genital Neisseria Gonorrhoeae Screening Among MSM

Background: CDC recommends annual screening of MSM for Neisseria gonorrhoeae (GC) at all exposed anatomic sites regardless of reported condom use.  Nucleic acid amplification tests (NAAT) have demonstrated higher sensitivity than culture, but no NAAT has been FDA-approved for use on non-genital specimens, requiring local labs to validate for clinical use.

Objectives: To determine the performance of the new BD ProbeTec^TM Q^X Amplified DNA Assay on the BD Viper^TM System with XTR^TM (BD Q^x) for non-genital GC screening of MSM.

Methods: From 11/2010-9/2011, patients provided three clinician-collected specimens from eligible anatomic sites.  Specimens were tested using gonorrhea culture, BD Q^x, and Gen-Probe Aptima Combo 2 (AC2).  Specimens were considered positive for GC if they were positive by culture or concordantly BD Q^x and AC2 positive.

Results: Three hundred ninety-four (394) patients consented to provide pharyngeal specimens and 147 consented to provide rectal specimens.  Pharyngeal GC prevalence was 8.9% and rectal GC prevalence was 13.6%.  BD Q^x identified 2.5 times more pharyngeal GC (33 versus 13) and 1.7 times more rectal GC infections than culture (20 versus 12).  For pharyngeal GC, observed sensitivity was 94.3% (95% CI: 80.8-99.3) and specificity was 96.7% (95% CI: 94.2-98.3).  For rectal GC, observed sensitivity was 100% (95% CI: 83.2-100) and specificity was 99.2% (95% CI: 95.7-100).  BD Q^x had PPV of 73.3% (95% CI: 58.1-85.4) for pharyngeal GC and 95.2% (95% CI: 76.2-99.9) for rectal GC.

Conclusions: The BD Q^x demonstrated high sensitivity/specificity for detecting non-genital GC infections and identified a large proportion of infections that would have been missed by using culture alone.  In light of the low observed PPV for pharyngeal screening, confirmatory testing with a second NAAT may be warranted.

Implications for Programs, Policy, and Research: Additional validation studies should be performed on the BD Q^x in order to determine if these results are replicable.