Markers of HIV infection prior to IgG antibody seropositivity.

During a 1-year period of study at two plasma collection centers, 7 of 35,000 plasma donors seroconverted to the human immunodeficiency virus (HIV) and had stored plasma samples that predated or antedated the seroconversion period. From each donor, three to eight plasma samples that had been collected at 2- to 7-day intervals were tested for IgG and IgM antibodies to HIV with enzyme immunoassays, Western blot testing, and radioimmunoprecipitation assays. The presence of an HIV viremic phase was demonstrated by the infectivity of plasma on normal, phytohemagglutinin-stimulated peripheral blood mononuclear cells and by the detection of HIV antigen. In 5 of these donors, HIV antigen was detected prior to or simultaneously with IgG to HIV; these HIV-antigen-positive samples overlapped an IgM immune response. The disappearance of detectable HIV antigen, and to a lesser extent plasma infectivity, was concurrent with the development of an IgG immune response. Although the improved sensitivity of a recombinant DNA-derived anti-HIV screening assay shortened the "window period" between initial HIV infection and antibody detection, HIV antigen and plasma HIV viremia were the only markers of HIV infection for several days in 2 donors. These results demonstrate that HIV plasma viremia and antigenemia occur prior to seroconversion in healthy plasma donors.