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Background: One of the measures aimed at reducing the risk of transmission of the agent responsible for the new variant of Creutzfeldt-Jakob disease was to exclude blood donors having stayed in the United Kingdom between 1980 and 1996. The objective of the study was to estimate the impact on the residual risk of HIV transmission of recruiting extra first-time donors to replace donors having stayed in the United Kingdom., Methods: The residual risk of HIV transmission due to donations made during the window period was estimated in all donations made in France during the 3-year period 1996-1998 by a linear combination of residual risks in repeat donors and first-time donors. In repeat donors, the estimate is based on the incidence rate of HIV in this population and in first-time donors on the "detuned assay" method. Seven simulations of the impact on the residual risk were made using various percentages of donors which would be excluded (from -5% to -35%)., Results: In all donations made in France during the 1996-1998 period, the residual risk of HIV transmission was estimated at 0.70 per million donations, which represents five to six donations made during the window period. If all the donors who had stayed in the United Kingdom were excluded from the donation (35%) and replaced by first-time donors, the residual risk of HIV transmission would be increased from 0.70 to 0.86 per million donations. This increase of 24% would represent one or two extra cases of post-transfusion HIV infection over a 3-year period., Conclusion: The results of this study show that the exclusion of a large number of blood donors, replaced by first-time donors, would have a low but quantifiable impact on the residual risk of HIV transmission. This increase of risk was one of the factors that led to the decision of not excluding donors having stayed in the United Kingdom between 1980 and 1996.

The evolution of viruses contributes to their diversification, whether it be a result of their own replication, or host-pressure dependent. Certain viral types, groups or subtypes are therefore found in certain regions of the world or in certain populations. The development of blood screening reagents is nearly always based on viral antigens or viral sequences derived from 'prototype' strains or antibodies raised against these prototype strains. Therefore in situations where an individual is infected by a viral strain that is genetically and antigenically distantly related to the prototype strain used in the development of the test, screening failure may occur. In the present article, this has been illustrated via 3 models, the human immunodeficiency virus (HIV), the hepatitis B virus (HBV), and the B19 parvovirus. Viral diversity also has a negative effect on the prevention of blood-transmitted viral infections. The example provided concerns vaccination failure and/or seroprophylaxis against hepatitis B.

The five available p24 Ag/anti-HIV combined tests were compared to the six third-generation anti-HIV assays mainly used in blood transfusion centers. Among 70 selected HIV-1 positive samples (12 samples from early infected blood donors and 58 from ten commercial panels), 59 were positive with at least one assay. False negative results were observed for zero to six samples with p24 Ag/Ab assays versus seven to 19 with antibody (Ab) tests. In five cases, one or more combined assays gave a positive signal later than the most sensitive Ab screening test. One sample with a high p24 Ag titer was missed by one combined test. The mean time delay between the most sensitive test and the second one was 0.3 to 2 days. The p24 Ag limit of detection was investigated with seven dilutions of the HIV Ag reference. The threshold of the p24 Ag detection was found to be between 65 and 250 pg/mL of HIV Ag. For four of the five combined assays, p24 Ag detectability was assessed with dilutions of infected culture cell supernatants from 13 HIV-1 different genotype strains exhibiting HIV Ag titers from 300 to 450 pg/mL. One of the four combined assays gave negative results but close to the cut-off for three supernatant dilutions (1 B, 1 F, 1 HIV-1/O) and one missed the HIV-1/O dilution. The p24 Ag/Ab combined assays permit an earlier diagnosis of HIV infection than third generation assays even if the yield in terms of reduction of the window period is moderate. They are less sensitive than p24 Ag screening assays for the detection of this marker. Consequently, the p24 Ag/Ab assays have not been used for the diagnosis of a primary infection instead of p24 Ag screening tests. They must be considered only as good tools for the detection of HIV infection.

From 1996 to 1998, a decrease in positive donation rates has been observed for HIV, HCV and HBs Ag in first-time donors, while these rates remained stable for HTLV. In repeat donors, the same decrease was observed for HCV and HBs Ag while the rates remained stable for HIV. No HTLV-positive donations from repeat donors were noted in 1998. About half of the HIV-positive repeat donors were regular donors (less than two years between the two donations), as well as 88% of HBV-infected repeat donors. Inversely, only 20% of HCV-positive repeat donors were regular donors. Anti-HBc antibodies have been found in 20% of HIV-infected donors, in 22% of HCV-infected donors, and were associated with HBs Ag in 99% of the cases. Elevated ALT was observed in 47% of donors with anti-HCV and in 10% of donors with HBs Ag. The major risk factors are at-risk sexual behavior for HIV and use of intravenous drugs and nosocomial infections for HCV. Being a native of an endemic country has been found to be the major risk for HBV. The major HTLV risk factor was directly or indirectly linked to the Caribbean area.

A comparative evaluation of the sensitivity of anti-HIV screening assays has been recently performed with a selected panel of 65 samples which included HIV1 group M (per-seroconversions, seroconversions and seropositives infected with genotypes A, B, C, D, E), HIV1 group O and HIV2. The results obtained with the 21 ELISA HIV1 + HIV2 screening assays are presented. Among these 21 assays, four are combined anti-HIV and p24 Ag assays. All the assays except four fulfilled the criteria defined at the beginning of the study, i.e., positive results on all the seropositives including seroconversions and positive results on at least 50% of the per-seroconversions. The main differences were observed with the ten per-seroconversion samples, the number of positive results on such samples varying from three to ten. The constant improvement of anti-HIV screening tests which leads one to shorten the 'window' period permits and earlier diagnosis of HIV infection and a progressive decrease of the transfusional risk.

The prevalence of HIV, HTLV, HBV and HCV infections has been calculated by age and sex of blood donors and not, as generally done, according to the number of donations. This study has been conducted on the basis of two surveys. The first one collected information about the sex and age of the seropositive donors. A second survey, begun in 1992, collected information about the demographic characteristics of blood donors. This population has a higher male to female sex ratio (1:2 versus 1:0) and is younger than the general population. Thus, the prevalence of these viral infections has been determined according to sex, age and type of donors (first-time or repeat) from 1992 to 1996 and the trends have been analysed. The main results are the following: a decreasing prevalence of HIV in first-time donors from 1992 to 1996, more marked in men than in women and in the 18-29 year age group than in the other age groups; a slighter decrease in prevalence of HBV and HCV in first-time donors from 1992 to 1996 with no difference in this decrease between sex and age groups. HBs Ag prevalence in first-time donors was twice as high in men than in women and was highest in donors aged from 40 to 49 years in both sexes. Prevalence of antibodies to HCV in first-time donors was comparable in both sexes but varied greatly with age. In men, a peak was observed in the 30-39 age group and in women, the highest prevalence was seen in the 50-65 age group.

A decrease of positive donation rates for antibodies to HIV, to HCV and for HBs Ag has been observed between 1993 and 1995 both in first-time and regular donations. In first-time donors, the most important decrease has been observed for HIV and in regular donors for HCV and HBs Ag. The interval between the negative and the positive donations was inferior to 1 year for 50% of regular donors and was superior to 2 years for 20 to 30%. About 30% of HIV positive donations were positive for other markers: 23% for anti-HBc and 10% for anti-HCV. About 40% of HCV positive donations had an elevated ALT level. Risk factors related to HIV heterosexual transmission appear to be the most difficult to identify during the donor selection and the least often associated with other markers. In recently HCV-infected donors, the main risk factors were IV drug addiction (25%) and nosocomial infection (30%). The major HTLV risk factor was directly or indirectly linked to the Caribbean area. Important differences between continental France and overseas territories were observed for HIV and HBs Ag rates.

In 1974, the existence of hepatitis serologically distinct from hepatitis A and B was recognized. They were tentatively designated non-A non-B. They accounted for 90% of post-transfusional hepatitis. During 15 years numerous studies failed to identify agent(s) responsible for these hepatitis. In 1989 the virus responsible for parenteral non-A non-B hepatitis was identified and named hepatitis C virus. Shortly after, the virus responsible for enteral non-A, non-B was also discovered (hepatitis E virus). During these 15 years, a 60% reduction of post-transfusional hepatitis was obtained both by the measures instituted to prevent AIDS transmission and by the introduction of surrogate assays (ALT levels and anti-HBc antibody).

Controls were performed using a common internal panel specific for anti-HIV, anti-HTLV and HBs Ag. During the past 32 months, 5 anti-HIV1 + 2 antibody kits (Abbott, Behring, Biotest, Murex D. and Organon T., total of 199 lots), 4 anti-HTLV I/II antibody kits (Abbott, Murex D., Organon T. and Ortho C.D., total of 153 lots) and 5 HBs Ag kits (Abbott, S.D. Pasteur, Murex D., Organon T. and Ortho C.D., total of 244 lots) were used and controlled by the 14 participating laboratories. Analysis of the results showed the values obtained for the most representative sample of each panel to be within the limits m +/- 2 SD in 95 to 100% of the HIV1 + 2 kits, in 94 to 97% of the HTLV kits and in 92 to 100% of the HBs Ag kits. The specificity of the kits evaluated was on an average equal or superior to 99.5%, as required by the French Drug Agency in a blood donor population.

The agent responsible of more than 80% of the parenterally transmitted non-A-non-B hepatitis, designated hepatitis C virus (HCV), was identified in 1988 thanks to the isolation of the first cDNA reactive clone which was derived from experimentally infected chimpanzees RNA. The recombinant protein expressed from this clone located in the NS4 region of the HCV, allowed to establish the whole HCV-RNA sequence and to develop the first generation enzyme-linked immunoassays for detecting anti-HCV antibodies. Subsequently, other recombinant viral antigens derived from other HCV genome regions, were produced and used to develop second generation screening and confirmatory assays (1991). At least, thanks to a better presentation of the epitopes, since 1993 the performance of third generation reagents have been improved. Nevertheless, in spite of those modifications, the performance of both screening and confirmatory assays still needs to be improved. Moreover, in cases of difficulties of HCV infection diagnosis with serological tests, HCV-RNA detection with genomic amplification tools represents a useful alternative.

This study estimates the risk of transmitting human immunodeficiency virus (HIV), human T lymphotropic virus (HTLV), hepatitis C virus (HCV) and hepatitis B virus (HBV) from blood units using a seroconversion incidence model. Data from 13 blood transfusion centers collecting about 1 million donations per year and belonging to the Retrovirus and the Viral Hepatitis study groups were analyzed during the 3 year study period (1992-1994) for HIV, HTLV, and HBV and a 2 year study period for HCV (1993-1994). Seroconversion incidence rates were calculated and multiplied by estimates of the serological window period for each agent to obtain residual risk. The risk that an infectious donation was made during the window period was estimated to be 1 in 2 millions (95% CI: 1/10(7)-1/450000) for HTLV, 1 in 588000 (1/3 300000-1/227000) for HIV, 1 in 217000 (1/714000-1/83000) for HCV and 1 in 112000 (1/333000-1/43500) for HBV. This risk was estimated for the totality of donations collected in France for HIV and HTLV. For HIV it was the same as above (1 in 588000) and for HTLV it was much lower (1 in 7 millions).

As it has been observed since the beginning of anti-HIV screening in blood donations, the rate of seropositive donations has been still decreasing during these 4 last years: 0.090/1000 in 1991 to 0.042/1000 in 1994. This decrease has been observed in blood donations from first-time donors (0.38 to 0.17/1000) and from regular donors (0.060 to 0.030/1000). However, the residual risk from cellular components, such as it is estimated, seems to be stable. The proportion of blood donations positive for both anti-HIV and anti-HBc was constantly decreasing from year to year: 63% between 1985 and 1988 and 25% in 1994. The repartition of seropositive donors into sex, ages and at-risk groups during this recent period was the same as previously observed.

A comparative evaluation of the sensitivity of anti-HIV screening assays has been recently performed with a selected panel including all the actually known difficulties of HIV serology: Very recent seroconversions (per-seroconversions) and recent HIV1/M seroconversions, HIV1/M seropositive with a subtype different from B, HIV1 group 0 and HIV2. The criteria of sensitivity were to recognize as positive all the seropositive samples and at least 2 of the 8 per-seroconversions. The 18 combined ELISA fulfilled these criteria, except for one assay with a deficient HIV2 sensitivity. However, all these assays do not have the same level of sensitivity. The most important differences were observed with the pre-seroconversion samples, the number of positive results on such samples varying from 2 to 8. The capacity of a screening assay to early detect an HIV-infected subject is a supplementary criterium to retain, particularly in blood transfusion screening, in order to shorten the "window" period.

The results concerning the hepatitis C antibodies screening tests sensitivity are presented by Viral Hepatitis Study Group of the French Society of Blood Transfusion. This evaluation was carried out in 1993, with five tests available for Hepatitis C Viral (HCV) antibodies screening. Several panels of human blood samples, collected by members of Viral Hepatitis Study Group, were used. For those specimens the data about whole serology (various reactivities against viral antigens) clinical history and other explorations (molecular biology, liver histology, other viral infections) are described. If possible all those results are used to describe some interpretation criteria for the HCV serology and sensitivity obtained for each screening test.

The combined HIV1 + HIV2 assays allow to screen simultaneously the subjects infected by HIV1 or by HIV2 (About 80 HIV1 for 1 HIV2 in blood donations in France). An improvement of both sensitivity and specificity was obtained by using artificial proteins which have been selected for having the most immuno-dominant epitopes. The sensitivity is defined by the study of samples from recent and very recent seroconverters and the specificity by testing 2000 unselected blood donors. All the early seroconversions must be recognized as positive and less than 0.5% false positive results must be found in blood donors. HIV1 variants, temporarily named sub-type O have brought a new difficulty to the HIV serology, due to a weak homology, especially in "env" domains, between these variants and the reference HIV1 strains. Subjects living in France and infected by this HIV1 variant seem rare and the screening assays which miss some of these infected individuals seem capable to modify their reagents in order to recognize all of them.