Compelling evidence supporting a cause-and-effect relationship between HIV and AIDS has come from studies of transfusion recipients with AIDS who have received blood from at least one donor with HIV infection. In the earliest such study (before the discovery of HIV), seven patients with transfusion-acquired AIDS were shown to have received a total of 99 units of blood components. At least one donor to each patient was identified who had AIDS-like symptoms or immunosuppression (Curran et al., 1984).

With the identification of HIV and the development of serologic assays for the virus in 1984, it became possible to trace infected donors (Sarngadharan et al., 1984). The first reports of donor-recipient pairs appeared later that year (Feorino et al., 1984; Groopman et al., 1984). In one instance, HIV was isolated from both donor and recipient, and both had developed AIDS (Feorino et al., 1984); in the other, the recipient was HIV antibody-positive and had developed AIDS, and the donor had culturable virus in his blood and was in a group considered to be at high risk for AIDS (Groopman et al., 1984). Molecular analysis of HIV isolates from these donor-recipient pairs found that the viruses were slightly different but much more similar than would be expected by chance alone (Feorino et al., 1984; Groopman et al., 1984).

In a subsequent study of patients with transfusion-acquired AIDS, 28 of 28 individuals had antibodies to HIV, and each had received blood from an HIV-infected donor (Jaffe et al., 1985b). Similar results were reported from a set of 18 patients with transfusion-acquired AIDS, each of whom had received blood from an HIV-infected donor (McDougal et al., 1985b). Fifteen of the 18 donors in this study had low CD4+/CD8+ T cell ratios, an immune defect seen in pre-AIDS and AIDS patients.

Another group studied seropositive recipients of blood from 112 donors in whom AIDS later developed and from 31 donors later found to be positive for HIV antibody. Of 101 seropositive recipients followed for a median of 55 months after infection, 43 developed AIDS (Ward et al., 1989).

More recently, Australian investigators identified 25 individuals with transfusion-acquired HIV whose infection could be traced to eight individuals who donated blood between 1980 and 1985, and subsequently developed AIDS. By 1992, nine of the 25 HIV-infected blood recipients had developed AIDS, with progression to AIDS and death more rapid among the recipients who received blood from the faster-progressing donors (Ashton et al., 1994).