HIV is transmitted to IDUs by parenteral exposure to contaminated injection equipment, including needles. Risk factors for infection include frequency of needle sharing, duration of injecting drug use, use of drugs in “shooting galleries,” and living in a community with a high prevalence of HIV infection in IDUs. Among IDUs, higher rates of HIV infection have also been associated with lower socioeconomic status, homelessness, and minority race-ethnicity. As has been true of homosexual men, many IDUs have changed behavior to reduce their HIV risk, particularly by reducing needle sharing. Studies suggest that drug abuse treatment, street outreach with counseling, and measures to make sterile injection equipment more readily available all have a role in reducing the risk of HIV infection among IDUs.

HIV has been transmitted by whole blood, plasma, cellular components, and clotting factors, but not by other products produced in the United States from blood. No HIV transmission has been linked to receipt of immune serum globulin, hepatitis B immune globulin, Rho (O) immune globulin, or hepatitis B vaccine. The latter products have been produced by fractionation and other processes that remove and inactivate HIV.

Conversely, receipt of whole blood, packed cells, or plasma from an HIV-infected donor has been shown to transmit HIV virtually 100% of the time. It has been estimated that >12,000 living persons in the United States were infected with HIV through blood transfusions, as were several thousand additional persons with hemophilia from infected clotting factor concentrates between 1978 and 1985. In the United States and most industrialized countries, screening of all donated blood and plasma for HIV, donor deferral procedures, and heat treatment of clotting factor concentrates have minimized the risk of HIV transmission through transfusions. The exceptions occur largely in donors very recently infected who have yet to develop detectable antibody.

This so-called window period is estimated to average 6 to 8 weeks after infection. The rate of HIV transmission from such HIV-seronegative donors was estimated to range from 1 in 36,000 to 1 in 225,000 units transfused in the United States, with even lower estimates in recent years. Because HIV transmission has been reported in recipients of organs, tissues, and semen from HIV-infected donors, the USPHS recommends that potential donors be screened for HIV antibody and that organ, tissue, and semen of those who test positive not be used for transplantation or insemination.