Suppression of plasma virus load below the detection limit of a human immunodeficiency virus kit is associated with longer virologic response than suppression below the limit of quantitation

Suppression of human immunodeficiency virus type 1 plasma virus load (PVL) to <20 copies/mL is associated with a longer virologic response after initi ation of antiretroviral therapy. The relationship between duration of virol ogic response and PVL nadir according to a less sensitive assay was explore d. When compared with subjects with a PVL nadir >500 copies/mL, the relativ e risks of PVL rising above 1000 copies/mL for participants in the INCAS tr ial and the British Columbia Drug Treatment Program with a PVL nadir below the limit of detection (LOD) were 0.04 (95% confidence interval [CT], 0.02- 0.09) and 0.06 (95% CI, 0.03-0.12), respectively. The corresponding relativ e risks for persons with a detectable but not quantifiable PVL nadir were 0 .25 (95% CI, 0.13-0.50) and 0.54 (95% CI, 0.25-1.19). The relative risks of virologic failure associated with a PVL nadir detectable but not quantifia ble and a PVL nadir below the LOD were statistically different (P < .0001) in both data sets.