C-162. The Affirm™ VPIII Test Classifies More Subjects Positive for Gardnerella vaginalis and Fewer Positive for Candida sp. than Culture

R. N. Amos1, R. C. Parke1, H. D. Engler2, M. B. Nye1, B. A. Body1;
1Lab. Corp. of America, Burlington, NC, 2Lab. Corp. of America, Raritan, NJ.

Background: The Affirm™ VPIII test uses DNA probes to detect nucleic acid from Candida species (CS), Gardnerella vaginalis (GV) and Trichomonas vaginalis for the diagnosis of vaginitis/vaginosis. Following validation and implementation of this test, we observed a high positivity rate for GV in clinical samples. Therefore, we undertook this study to compare the performance of Affirm™ VPIII for GV and CS with culture. Methods: Sixty-nine volunteer subjects were recruited from the workplace. Subjects self-collected multiple vaginal swabs in random order using the Ambient Temperature Transport System (ATTS). Symptoms were not assessed or reported. Affirm™ VPIII (Becton, Dickinson and Co.) testing was performed immediately on one ATTS according to manufacturer’s instructions; additional ATTS were tested 24 and 72 h post collection. To simulate transit, a culture swab was used to inoculate a 5% sheep blood plate for general vaginal culture, a V-agar plate for GV culture and a SAB-HI with gentamicin plate for CS culture 24 h post collection. Standard laboratory techniques were used to identify GV and CS.Results: Ten subjects were positive for GV by culture and Affirm™ VPIII at all time points. Twenty-nine additional subjects were positive for GV by Affirm™ VPIII at ≥1 time point but had negative GV culture. Uninoculated ATTS gave false positive GV Affirm™ VPIII results. Eight subjects had moderate or heavy growth of CS; 4/8 had positive Candida Affirm™ VPIII results at ≥1 time point. Of 10 subjects with light to rare CS growth and 51 subjects with no growth of CS in culture, no positive Candida Affirm™ VPIII results were obtained. Conclusions: Using culture results as the gold standard in this population of volunteers with unknown symptom status, Affirm™ VPIII demonstrated 100% sensitivity but poor specificity for GV; 74% of positive GV Affirm™ VPIII subjects failed to confirm by culture. Conversely, for CS, Affirm™ VPIII was less sensitive than culture, detecting CS in 50% of subjects with moderate or heavy growth of CS in culture. Affirm™ VPIII classifies more subjects positive for GV and fewer subjects positive for Candida sp. than culture.