Human immunodeficiency virus type 1 (HIV-1) infection a median of 18 months before a diagnostic western blot. Evidence from a cohort of homosexual men.

To study the natural history of human immunodeficiency virus type 1 (HIV-1) infection, we used an in-vitro amplification technique to detect HIV-1 nucleic acid sequences in sequential aliquots of peripheral blood mononuclear cells from homosexual men enrolled in the Multicenter AIDS Cohort Study. Blinded, longitudinal study of 24 homosexual men who were positive for HIV-1 antibodies at a recent follow-up visit. Coded clinical samples were evaluated using two enzyme-linked immunosorbent assays (whole virus and gp120-gp41 fragment), Western blot, a p24 antigen capture assay, virus cocultivation, and in-vitro amplification of conserved regions from the HIV-1 gag and env open-reading frames. In 20 of the 24 men an HIV-1 enzymatically amplified product was detected before HIV-1 antibody seroconversion: at 42 months before seroconversion in two cases; at 36 months in one case; at 30 months in one case; at 24 months in four cases; at 18 months in eight cases; at 12 months in one case; and at 6 months in three cases (median, 18 months). In the four other men, detection of an HIV-1 enzymatically amplified product was concurrent with confirmation of antibody seroconversion by Western blot. There is a long and variable interval between virus acquisition and a diagnostic serum antibody response, perhaps due to the prolonged, persistent infection characteristic of the lentiviruses (family Retroviridae).