Blood and Blood Products Safety and Risk (1996) / Chapter Skim
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1: Current Risks of Disease Transmission
1: Current Risks of Disease Transmission
Pages 1-24
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I Current Risks of Disease Transmission
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Seventy to 80 percent of donors in the United States are now repeat donors Finally, and what the public focuses on most, is serologic screening, which in fact may be the least important of the preventive measures. A paper published in Transfusion2 by Michael Busch from the Irwin Memorial Blood Bank in San Francisco showed that during the late 1970s and early 1980s, transfi~sion-transmitted HIV infections in San Francisco were a substantial problem.
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The second approach has been to test the blood in the blood banks by a more sensitive technique such as DNA PCR (deoxyribonucleic acid polymerase chain reaction)
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The second of the three approaches to estimating the risk of HIV transmission from HIV antibody-screened blood was taken by G.N. Vyas and colleagues at the Irwin Memorial Blood Center in San Francisco.
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. Evaluation of screened blood donations for human immunodeficiency virus type 1 infection by culture and DNA amplification of pooled cells.
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Consensus Development Conference in January 1995, he reported 33 cases of HIV infection in repeat donors in 822,000 person years, for an overall incidence rate of 4 per 100,000 person years.9 Using a window period estimate of 22 days yields an estimated risk of transfusion during the window period of 2.4 per million (1 in 416,000~. The HIV prevalence rates in firsttime donors are higher, which could also mean that HIV incidence may be higher among first-time donors, and therefore they are at higher risk of being in the window period.
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test, and the serologic test for syphilis, actually function as surrogate markers for HIV, eliminating some HIV-infected but antibody-negative donors because of positivity on these other screening tests. In fact, one of the reasons for the recent NIH Consensus Development Conference recommendation to retain the HBV core antibody test was for its value as a surrogate marker for HIV (as well as a direct marker for HBV infection)
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The current estimate of the number of HIV-infected donors in the United States can be calculated from the risk data presented above. If the risk is 1 in 420,000 units and 13 million units per year are collected, then we might expect roughly 50 HIV infections per year.
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The second-generation assay is now used to screen donors, so the best estimate of the current risk is about 3 per 1 0,000. A recent paper by Blajchman and colleagues from Canada's reported a controlled study in which they assigned 4,500 patients to receive blood that either was or was not tested for surrogate markers (anti-HBV core antigen and ~3Donahue, JG, A Munoz, PM Ness, DE Brown, DH Yawn, HA McAlister, BA Reitz, KE Nelson (1992)
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To estimate the rate of transfusion-transmitted HBV, we screened transfused patients before and 6 months after their transfusion for antibodies to HBV core antigen. There was only about a twofold increase in the rate of incident HBV infections in the transfused patients compared to the incidence among those who were not transfused; the incidence of HBV infections among transfused patients was about tenfold lower per unit of blood than we found for HCV infections in the same study population.
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These data suggest that if we had tested donors for HBV core antibody in the middle and late 1970s, we might have prevented some transfusion-related HBV infections even though these donors had been found negative for hepatitis B surface antigen. The incidence of infection with HIV, HTLV, HCV, and HBV has very recently been determined for the 586,507 repeat donors in REDS.
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. NIH Consensus Development Conference on Infectious Disease Testing for Blood Transfusions, January 9-11, 1995, Bethesda, Maryland.
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. A new subtype of human immunodeficiency virus type 1 (MVP-5180)
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These case suggest that there will be a continuing need for rapid development, evaluation, and licensure of new screening tests in order to maintain the safety of the blood supply. 26Loussert-Ajaka, I, TD Ly, ML Chaix (1994)
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Virus inactivation technology is in widespread use in the preparation of coagulation factor concentrates, and validated virus inactivation methods are beginning to be applied to all blood protein solutions including immune globulins and fresh frozen plasma (FFP)
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, Virological Safety Aspects of Plasma Derivatives, Developments in Biological Standardization, 81: 147-161; updated with information on file. The commonly employed viral elimination procedures are: .
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Methods of thermal inactivation are advantageous in that all classes of virus are potentially susceptible, although nonenveloped viruses tend to be heat stable. Because thermal inactivation methods are not inherently specific, means of stabilizing proteins while achieving excellent virus inactivation had to be identified.
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As examples, antibody affinity purification validated as a virus removal method has been combined with either S/D or heat treatment; some products are now treated by both S/D and heat; other products have been processed through virus-removing filters that have been developed recently and added to existing processes. New methods of viral inactivation under exploration include the use of chaotropes such as sodium thiocyanate, shortwavelength ultraviolet light in the presence of antioxidants, microwave heating, extraction with supercritical fluids, and iodine.
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Success with the sterilization of coagulation factor concentrates encourages research into the sterilization of blood components, i.e., FFP, red blood cell concentrates (RBCCs) and platelet concentrates.
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Red Blood Cell Concentrates. Numerous methods have been investigated, including the use of beta-propiolactone, nitrogen mustards, aryl diol epoxides, ozone, and halogenated oxidizing agents, but the best results described thus far employ photodynamically active sensitizers and visible light.
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Pooled blood products that have been virally inactivated meet this standard for most viruses, and use of a second viral elimination procedure that complements the first one will further ensure the safety of these products. Incorporation of viral inactivation procedures into the manufacture of all blood products, including blood cell concentrates, overcomes the weaknesses of screening procedures, and the further development of virus inactivation methodologies should continue to be encouraged.
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