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

Abstract

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.