The significance of low-level plasma HIV viral load on COBAS TaqMan HIV-1 assays for patients with undetectable plasma viral load on COBAS Amplicor monitor version 1.5.

BACKGROUND: COBAS TaqMan assay is a new HIV assay for measuring plasma viral load (VL). A significant number of patients with undetectable plasma VL on Amplicor assay were reported to have detectable VL with TaqMan in the study centre.
PURPOSE: The aim of the present study was to investigate the significance of detectable VL counts with TaqMan assay amongst patients who have had undetectable plasma VL with COBAS Amplicor assay.
METHOD: Observational study on patients who have had undetectable (<less than 50 copies/mL) plasma VL with COBAS Amplicor version 1.5 assay but detectable plasma VL with COBAS TaqMan assay between June 1, 2006 and April 30, 2007. All patients were on highly active antiretroviral therapy (HAART) for longer than 6 months before use of COBAS TaqMan assay. Patients with detectable VL were followed up on a monthly basis until their VL was <40 copes/mL or there was confirmed new resistance to HAART using genotypic and Virco resistance assay.
RESULTS: Plasma VL was detectable (>40 copies/mL) in 113 (14%) patients on 126 episodes using TaqMan assay. VL was less than 500 copies/mL in 90% of those episodes. All episodes ended with VL <40 copies/mL after a median of 117 (94-143) days without change in HAART regimes. The duration of those episodes was longer than 150 days in 75% of cases. No new mutation was detected amongst specimens with detectable VL.
CONCLUSION: Short-term detectable VL may be common with using TaqMan assay. This phenomenon did not result in new mutations or failure of HAART in study patients in the short term.