Every year in the United States approximately 12 million donations are collected from volunteer blood donors. These donations are separated into an average of three components, including red blood cells, platelets, and plasma. Ln addition, approximately 12 million units of plasma are collected by plasmapheresis from paid donors and pooled to manufacture plasma-derived products, such as immune globulin (IG) preparations, clotting factor concentrates, and albumin. During the past few decades, important changes in the way blood is collected, processed, stored, and transfused have helped reduce the risk of known transfusion-associated infections. Plastic containers introduced in the 1950s made it possible to separate blood components in a closed system, which markedly decreased the risk of bacterial contamination.(11) The advent of an assay for hepatitis B surface antigen (HBsAg) in the late 1960s, and the ensuing screening of blood for this marker, contributed to reducing the risk of transfusion-transmitted hepatitis.(47) Unfortunately, these advances were modulated in the early 1980s by the AIDS epidemic; over 4000 persons developed AIDS after becoming infected with HIV from unscreened blood.(71) BY th, time a heat inactivation procedure was introduced in the manufacture of clotting factor concentrates from plasma, approximately half of the United States hemophilia population had become infected with HIV.(48) A decade later, the repercussions of this tragedy still impacts transfusion medicine, resulting in magnified perceptions of the actual risks associated with this medical intervention. Because blood is a biologic product, it is unlikely that the risk of transfusion-transmitted infections will ever be reduced to zero. A residual risk remains, for example, for transmission of hepatitis C virus (HCV)(6,69) and for HIV infection.(16) Nonetheless, the blood supply in the United States in the 1990s is among the safest in the world, and is safer now than it has ever been.(80) Factors contributing to the reduced risk of transfusion-transmitted infections include improvements in donor selection, donor screening by serologic tests and other markers of infection, and viral inactivation procedures for plasma-derived products. Blood donors are subjected to extensive interviews to exclude persons with a history of exposures or behaviors that increase their risk of harboring transmissible agents. All blood donations are routinely screened for syphilis, hepatitis B virus (HBV), HCV, human T-lymphotropic virus type I (HTLV-I), HIV-1, and HIV-2; selected donations are additionally screened for cytomegalovirus. Plasma used in the manufacture of clotting factors and other plasma-derived products is subjected to heat treatment or other procedures that inactivate lipid-enveloped viruses, such as HIV,HBV, and HCV. These approaches, coupled with surveillance to monitor for trends in infection, constitute the backbone of public health strategies to protect the blood supply from known pathogens and to monitor for the emergence of new infectious agents. A number of challenges have faced blood safety in recent years, including variant HIV strains inconsistently detected by licensed HIV tests,(66) transmission of HCV through an intravenous immune globulin (IVIG) product,(14) a cluster of hepatitis A virus infection among hemophilia patients,(73) contamination of an albumin preparation,(22) and finding a porcine parvovirus in a porcine factor Vm product (Centers for Disease Control and Prevention [CDC], unpublished data). In addition, for an increasing number of emerging infectious agents, such as human herpesvirus 8 (HHV-8),(12) and putative human agents, such as Borna disease virus,(36) questions of transmissibility and risk of transmission by blood and blood products have arisen. Experimental evidence supporting transmission of prions by blood has raised concerns about the risk of transmission of Creutz-feldt-Jakob disease (CJD) to recipients of blood and blood products.(15,57) Finally, as the blood supply in the developed world has become increasingly safe, economic factors continue to prevent the institution of much-needed safety measures, such as HIV serologic tests, in much of the developing world. This article discusses some of these emerging issues in blood safety.
