All blood collected in the U.S. is now screened for six infectious agents: HIV-1, HIV-2, HTLV-1, hepatitis B virus, hepatitis C virus, and syphilis. All potential donors are interviewed before they are tested and informed that if they have a risk factor for HIV they should not donate. Every unit of donated blood with a positive result from HIV antibody testing is discarded, and future donations are not accepted from those persons.

Historical information shows that, as of the end of June 1992, CDC had received reports of 4,959 AIDS cases (300 of these in children under 13) resulting from receipt of blood transfusions, blood components, or tissue. Most of these cases are due to transfusions received before March 1985, when HIV screening of blood and blood products began; only 21 cases (out of the total 4,959) have resulted from screened blood. In March 1987 CDC recommended that physicians consider offering HIV antibody testing to patients who received transfusions between 1978 and late spring of 1985.

Studies estimating the risk of becoming infected with HIV from a blood transfusion screened as negative for HIV antibody have been conducted. Early estimates ranged from 1 in 38,000 to 1 in 300,000 per unit of transfused blood. A study by the University of California, San Francisco, of blood donations made in San Francisco between November 1987 and December 1989 estimated this risk to be around 1 in every 61,000 units of transfused blood. A study using data from more than 17 million American Red Cross blood donations in 1987 estimated that the odds of contracting HIV infection were roughly 1 in 153,000 units of transfused blood. A recent study by CDC and the American Red Cross of Red Cross blood donors, or approximately half of the U.S. blood supply, estimated that the risk of HIV transmission from screened blood in 1990 was 1 in 225,000 units.

These figures are accurate for the populations studied and the periods in which the studies were conducted. They provide useful information for estimating this risk for the general population. It is important to understand that HIV infections from transfusions of blood screened as negative for HIV antibody have been extremely rare and have become progressively infrequent, even in areas with high HIV prevalence rates.