Current concepts in transfusion transmitted diseases

Abstract

During the 1950's, 25{%} of recipients of 4 or more whole blood transfusions in New York City developed jaundice and this was accepted as a “fact of life.” Until the 1970's, the only transfusion transmitted diseases of concern were syphilis and “serum hepatitis” later recognized as hepatitis B screened by HBsAg assays. In the early 1980's, the tragedy of AIDS brought tragic consequences for blood recipients but also brought attention and resources to the prevention of transmission of infections by blood transfusion. These included a movement towards volunteer donors as opposed to replacement and paid donations, stricter donor eligibility criteria, donor deferral lists, introduction of quality systems, active regulatory oversight and testing of donated blood for communicable agents. New tests were introduced, including in many countries ALT, HBcAb (core), antibodies to HIV, HTLV-I/ II, HCV, and some confirmatory assays. More recently molecular assays for HIV, HCV and HBV were also implemented in several countries. Different technologies address different issues. Serological assays detect antibodies against the infectious agent (signal amplification results from the immune response) while molecular assays detect the nucleic acid sequences, RNA or DNA through amplification that takes place in the test tube. Serological assays are effective for detection of antibodies in infected individuals in a population, or prevalent cases. Molecular assays (nucleic acid amplification tests or NAT) are effective for the detection of recent infections, or incident cases. In some instances, like detection of parasitic infections, serological tests are more effective because the few parasites present in a component may be sufficient to transmit infection but may be missed in the small specimen used for testing (Poisson distribution). Test selection must also consider regional epidemiology. Screening for hepatitis B (HBV) in a low prevalence area may be based on a combination of assays that include HBV surface antigen or HBsAg, antibodies to core of HBV (HBcAb) and NAT for HBV, depending on availability and resources. Selection is more difficult in high prevalence areas because a large segment of the population has been exposed to HBV and is positive for HBcAb, and often resources for the implementation of NAT are not available; thus, screening must rely on high sensitivity HBsAg assays. Regional epidemiology has also been a factor in the selective approach chosen for T. cruzi in the U.S. and HTLV-I/II in Europe. Serological assays are not effective for Dengue, West Nile Virus and probably other arboviruses because they are only transmitted when there is viremia which gradually vanes after the appearance of antibodies. Despite public demand for unattainable “zero risk,” investments in transfusion safety also need to be balanced with other healthcare priorities appropriate for each environment. However, we cannot continue to add screening assays for every newly recognized pathogen transmissible by transfusion. Hopefully, in the foreseeable future, safe and effective pathogen inactivation technologies will allow us to limit the number of screening assays needed to ensure the safety of the blood supply.