Performance of the Aptima Analyte Specific Reagent Assay for Detection of T. vaginalis

Background:
T. vaginalis (TV) is the most common non-viral STD worldwide and has been linked with increased risk of HIV acquisition. Testing for this pathogen should be routinely included with screening for C. trachomatis (CT) and N. gonorrhoeae (GC). However, few commercial assays are available for this purpose. Ideally, TV diagnostics should be based on highly sensitive nucleic acid amplification methodologies.

Objective:
To evaluate the performance of a commercially available, RNA-based analyte specific assay (ASR) that uses the same platform as the APTIMA Combo 2 CT/GC assay (GenProbe, San Diego).

Method:
TV PCR using a modification of the Amplicor CT/NG platform (Roche, Indianapolis) has been in use in our laboratory since 1998. Residual urine samples were stored in Aptima transport medium for later testing. The sample set was intentionally enriched for positive specimens. Results of the Aptima assay for TV (TV ASR) were compared to the TV PCR assay. κ scores and paired Pearson's correlation statistics were used to compare the two assays.

Result:
Ninety-seven samples were tested by both assays. The PCR assay identified 34 infections. The optical readouts of the two assays were highly correlated (ρ=.73, p<.001). The interpretations of the results (i.e. positive or negative) were also highly related with a κ score of .933 (p<.001). Using the PCR method as the gold standard, the TV ASR correctly identified 100% of positive samples and 96.8% of negative samples when a cut-off of 50,000 relative light units was used.

Conclusion:
The TV ASR performs well using urine samples and can be performed in laboratories that currently the perform APTIMA Combo 2 assay.

Implications:
Improved diagnostic assays that can be performed when screening for CT and GC are an important step toward improving public health control of T. vaginalis.