How reliable is an undetectable viral load?

Abstract

Objectives: An article by the Swiss AIDS Commission states that patients with stably suppressed viraemia [i.e. several successive HIV-1 RNA plasma concentrations (viral loads, VL) below the limits of detection during 6 months or more of highly active antiretroviral therapy (HAART)] are unlikely to be infectious. Questions then arise: how reliable is the undetectability of the VL, given the history of measures? What factors determine reliability? Methods: We assessed the probability (henceforthtermed reliability) that the n + 1 VL would exceed 50 or 1000 HIV-1 RNA copies/mL when the n th one had been < 50 copies/mL in 6168 patients of the Swiss HIV Cohort Study who were continuing to take HAART between 2003 and 2007. General estimating equations were used to analyse potential factors of reliability. Results: With a cut-off at 50 copies/mL, reliability was 84.5% (n = 1), increasing to 94.5% (n = 5). Compliance, the current type of HAART and the first antiretroviral therapy (ART) received (HAART or not) were predictive factors of reliability. With a cut-off at 1000copies/mL, reliability was 97.5% (n = 1), increasing to 99.1% (n = 4). Chart review revealed that patients had stopped their treatment, admitted to major problems with compliance or were taking non-HAART ART in 72.2% of these cases. Viral escape caused by resistance was found in 5.6%. No explanation was found in the charts of 22.2% of cases. Conclusions: After several successive VLs at < 50 copies/mL, reliability reaches approximately 94% with a cut-off of 50 copies/mL and approximately 99% with a cut-off at 1000 copies/mL. Compliance is the most important factor predicting reliability. © 2009 British HIV Association.