Comparison of Commercial Nucleic Acid Amplification Assays for the Detection of Neisseria gonorrhoeae, Chlamydia trachomatis and Trichomonas vaginalis
We compared the Seegene Allplex STI4 assay to the Hologic Aptima Combo 2 and Aptima Trichomonas vaginalis (TV) assays, for the detection of Neisseria gonorrhoeae (GC), Chlamydia trachomatis (CT) and TV.
A total of 418 pre-tested, frozen clinical specimens were supplied for this study, which had been run previously on the Hologic Aptima Combo 2 assay and/or Aptima TV assays. Specimens were frozen at -80°C after testing, and included Aptima vaginal, unisex (urethral and cervical) swabs, and urines. There were 107 CT, 64 GC and 50 TV positive specimens (including 18 co-positives) and 216 negatives tested. Primary specimen containers were de-capped, swabs were removed, then were extracted on the Hamilton STARlet. The BioRad CFX96 Real Time PCR Detection System and Seegene Viewer software were used to obtain and analyze results. Results were then compared to Aptima testing to assess sensitivity and specificity of the Seegene STI4 assay. Repeat Aptima testing was performed in discordant cases, to determine if the specimen was still positive after freeze/thaw cycles. For any remaining discordant CT or GC specimens, the Aptima confirmatory test (using a second primer set) was performed with the specimen called positive if both the Aptima Combo 2 and confirmatory assay was positive for the target. For TV, specimens positive on Allplex only underwent sequencing. Otherwise, the Aptima results were considered the gold standard.
The Seegene STI4 assay provided accurate results in 411 of 418 specimens (98.3%) as shown in Table 1. The sensitivity and specificity for GC was 100%. TV had a sensitivity of 96.1% and a specificity of 100.0%. For CT, the sensitivity was 95.3% and the specificity was 100%. In all cases of decreased sensitivity, false negatives were attributed to specimens with lower relative light unit values by Aptima testing.
The Seegene STI4 assay performed well in the detection of sexual transmitted infections. A drawback to the Seegene system is the need to de-cap and remove swabs from the sample tubes before running them on the extractor, which hinders work flow and is a potential source of contamination. Seegene is experimenting with pierceable caps to determine if this aspect of workflow can be improved.