Steady-state calculation of the risk of HIV infection from transfusion of screened blood from repeat donors.

All blood donations in the United States are screened for human immunodeficiency virus (HIV), the virus that causes AIDS; in spite of this, potentially infectious donations are still made by donors who are infectious but have not yet developed detectable HIV antibodies. A steady-state model for blood donations is used to calculate the expected number of potentially infectious blood donations made by repeat blood donors in a specified time interval. The expected number of potentially infectious donations made by each infectious blood donor who subsequently becomes HIV positive is calculated, and estimators of this quantity are presented. The relative risks due to donations from repeat and first-time donors is discussed. Estimates of the proportion of all blood donations made at 19 American Red Cross regional blood centers that are potentially infectious are presented.