[Viral risks associated with blood transfusion]

The presence of viruses in blood cells or plasma from asymptomatic donors is the major risk of transmitting an infectious agent through blood transfusion. The main viruses involved are hepatitis viruses and retroviruses. The risk of transmitting hepatitis B virus (HBV) and hepatitis C virus (HCV) has been progressively and efficiently reduced in the last years by the successive introduction of hepatitis B surface antigen (HBsAg) screening, elevated serum alanine aminotransferase (ALT), antibody to hepatitis B core (HBc Ab), and more recently antibody to hepatitis C virus (HCV Ab). The risk of transmitting human retroviruses like human immunodeficiency virus (HIV) and human T-cell leukemia/lymphoma virus (HTLV) has also been reduced drastically thanks to screening for corresponding antibodies. However, except for HBs Ag screening, the immunoassays used for HCV, HIV, or HTLV only detect antibodies. Therefore, although they are infectious, a few blood units may be not discarded. The efficacy of preventive measures depends on the incubation time, the infectivity during this silent phase, and the sensitivity of screening procedures. Human cytomegalovirus (HCMV) and parvovirus B 19 are responsible for common infections. Consequently, 30% to more than 50% adults have serologic evidence of past infection. However, both viruses may cause severe primo-infections in some circumstances, especially in pregnant women or immunodeficient individuals.