Time of exposure and risk of HIV infection in homosexual partners of men with AIDS.

We interviewed, and tested for HIV antibody, 117 homosexual men who had been regular sexual partners of men who developed acquired immunodeficiency syndrome (AIDS); 85 tested seropositive. Receptive anal intercourse with the index AIDS case and number of different sexual partners with whom subjects were anally receptive were both risk factors. Controlling for the number of partners with whom subjects were anally receptive, we found that the odds ratio of receptive anal intercourse with the case was infinite (95% confidence intervals, 3.3-infinity) if sexual contact continued up to or beyond the time of diagnosis, while the odds ratio was 1.0 (95% CI 0.3-3.2) if contact ceased before the case's AIDS diagnosis. Risk was not associated with the duration or frequency of contact. Our data suggest that the potential for sexual transmission from an HIV-infected person may be greater close to or after the onset of disease.