The contribution of statistics in the forensic appraisal of post-transfusion contamination by hepatitis C virus

Many patients were contaminated by blood products in the 1980s and early 19 90s, a period during which there was no means of detecting hepatitis C viru s (HCV) and measures of vigilance in French blood transfusion centers were lacking in rigor, and it has become a real public health issue by now. The blood transfusion centers which produce and distribute the products are lia ble for such contamination, as long as the expert appraisal has established a link of causality between the transfusion and the contamination. When th e viral serologic status (i.e. the contaminating potential) of the donors i s not known, experts often resort to indirect evidence, including use of pr obability estimates calculated according to the following method. The proba bility (P) that there was at least one contaminating donor among those havi ng provided the blood given to a patient, is calculated using the following formula: P = 1.(1.pHCV)(N) where pHCV is the prevalence of subjects who have tested positive fur anti- C virus antibodies in a population of blood donors, and N is the number of donors having contributed to the transfusion in question. Although the poly merase chain reaction (PCR) is very sensitive, its threshold, below which w eak replication is undetectable, varies depending on the technique used. On e study has demonstrated that below a dilution of 10(-4), RNA is no longer detected by the majority of laboratories. The specificity of PCR is not fla wless either, since false-positive results are found, probably resulting fr om contamination of the samples. Considering that 0.10% is a reasonable app roximation of the prevalence of subjects who had anti-HCV antibodies that w ere detectable by recombinant immunoblot assay during that period, one can calculate the probability that there is a contaminating donor among the blo od donors who contributed to the product that was administered and determin e a curve. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.