Risk of human immunodeficiency virus (HIV) transmission by anti-HIV negative blood. Estimates using the lookback methodology.

We have estimated the risk of transmitting HIV infection from a unit of HIV seronegative blood collected in Los Angeles and Orange Counties, CA from March 1985 through February 1987. Our method consisted of lookback investigations and anti-HIV testing of living recipients of HIV seronegative units donated by persons who later tested HIV seropositive at the time of a subsequent donation. During these investigations we have documented 3 cases of HIV transmission from HIV seronegative blood; using several assumptions, and extrapolating from this data, we have calculated that the risk of HIV transmission from an HIV seronegative unit was 1 in 51,000 to 1 in 102,000 (with a best guess of 1 in 68,000). We believe that our model can be applied in other geographic regions in an ongoing fashion in order to update our estimates of HIV transmission from HIV seronegative blood.