Reducing the risk of infection from plasma products: specific preventativestrategies

Collection and testing procedures of blood and plasma that are designed to exclude donations contaminated by viruses provide a solid foundation for th e safety of all blood products. Plasma units may be collected from a select ed donor population, contributing to the exclusion of individuals at risk o f carrying infectious agents. Each blood/plasma unit is individually screen ed to exclude donations positive for a direct (e.g. viral antigen) or an in direct (e.g. anti-viral antibodies) viral marker. As infectious donations, if collected from donors in the testing window period, can still be introdu ced into manufacturing plasma pools, the production of pooled plasma produc ts requires a specific approach that integrates additional viral reduction procedures. Prior to the large-pool processing, samples of each donation fo r fractionation are pooled ('mini-pool') and subjected to a nucleic acid am plification test (NAT) by, for example, the polymerase chain reaction (PCR) to detect viral genomes tin Europe: HCV RNA plasma pool testing is now man datory). Any individual donation found PCR positive is discarded before the industrial pooling. The pool of eligible plasma donations (which may be 20 00 litres or more) may be subjected to additional viral screening tests, an d then undergoes a series of processing and purification steps that, for ea ch product, comprise one or several reduction treatments to exclude HIV, HB V, HCV and other viruses. Viral inactivation treatments most commonly used are solvent-detergent incubation and heat treatment in liquid phase (pasteu rization). Nanofiltration (viral elimination by filtration), as well as spe cific forms of dry-heat treatments, have gained interest as additional vira l reduction steps coupled with established methods. Viral reduction steps h ave specific advantages and limits that should be carefully balanced with t he risks of loss of protein activity and enhancement of epitope immunogenic ity. Due to the combination of these overlapping strategies, viral transmis sion events of HIV, HBV, and HCV by plasma products have become very rare. Nevertheless, the vulnerability of the plasma supply to new infectious agen ts requires continuous vigilance so that rational and appropriate scientifi c countermeasures against emerging infectious risks can be implemented prom ptly. (C) 2000 Harcourt Publishers Ltd.