Samples collected prior to 1997 were tested using nucleic acid sequence-based amplification (NASBA) HIV-1 RNA QT (NASBA, bioMerieux, Boxtel, Netherlands). Samples with a viral load below the quantification threshold of the NASBA assay (1,000 copies/ml, n = 68), were re-tested in 2008 using the RealTime HIV-1 assay (Abbott Laboratories, Abbott Park, IL) with a threshold of 40 copies/ml. Viral load data were analyzed after log10 transformation. Viral load set-point was defined as the relatively steady level of HIV-1 RNA at 18–24 months after seroconversion. Set-point viral load data were available for 385 (301 MSM and 84 DU) participants.
