Assays for viral sequences and their value in validation of viral elimination

Plasma pools and blood products were analysed for hepatitis C virus (HCV) RNA by the polymerase chain reaction (PCR). Initially, samples were amplified by "nested" PCR using two pairs of primers from the highly-conserved 5' non-coding region of the genome. The method was later modified to amplification with only the outer pair of primers and a "hot-start" to eliminate amplification of non-target sequences. The modified method was as sensitive as "nested" PCR. However, with samples containing low levels of RNA, it is necessary to perform repeat amplifications to avoid false-negative results. Ten out of 17 anti-HCV positive pools from paid donors were positive, while none of the 12% pools from unpaid donors was positive for RNA or anti-HCV antibodies. Four i.v. immunoglobulins made from contaminated pools were virus-free, indicating removal of virus during current manufacturing processes. A quantitative PCR method was established using a positive donation. Probit analysis gave an estimated viral titre of 3.6 x 10(6) genomes/ml.