Background: I n October 2006, the FDA approved the Genprobe APTIMA HIV-1 RNA Qualitative Assay (Aptima) to confirm HIV-1 infection in persons with specimens repeatedly reactive for HIV-1 antibodies. However, Aptima is not currently approved to confirm a single reactive rapid test result. We sought to assess the performance of Aptima to confirm single reactive rapid test results.

Methods:  We assessed the performance of Aptima with specimens collected during a study to evaluate the performance of FDA-approved rapid tests. A total of 5743 persons screened for HIV infection and 497 persons known to be HIV-infected (some on ART) had specimens available for Aptima testing. Sera were collected for confirmatory testing by Western blot, and frozen remnant plasma specimens were later tested with Aptima at the US Centers for Disease Control and Prevention (CDC). When plasma was available, specimens with discordant Aptima and Western blot results were also tested by the Roche (Amplicor) 1.5 Ultrasensitive HIV-1 RNA assay.

Results:  Aptima was reactive for 273 (97.5%) of 280 newly diagnosed vs 398 (80.1%) of 497 previously diagnosed persons with reactive rapid test results confirmed by Western blot (p <0.001). Of persons with a prior HIV diagnosis, Aptima was reactive for 105 (98.1%) persons not on ART vs 293 (75.1%) persons on ART (p <0.001). Aptima correctly resolved 32 (100%) specimens with falsely-reactive rapid test results and negative Western blot as non-reactive. Aptima also resolved 5 specimens with reactive rapid test and indeterminate Western blot as reactive. The median HIV viral load of 16 specimens with reactive Aptima results but negative or indeterminate Western blot results tested by Amplicor was 199,410 (range 294 to 631,290) copies/mL, suggesting the specificity of Aptima in this sample of nearly 5500 specimens was 100%.

Conclusions:  Among persons with no prior HIV diagnosis, Aptima failed to confirm HIV infection for <3% of specimens that had single reactive rapid test results. Aptima failed to confirm one-quarter of single reactive rapid test results on specimens from persons taking ART. These data suggest that Aptima could be used to confirm single reactive rapid test results in persons without prior HIV diagnosis. However, when Aptima is nonreactive, other serologic methods and/or testing using specimen collected on follow-up would still be required to confirm or rule out HIV infection. Aptima is less useful for confirmation of HIV infection for persons taking ART.