Performance of third-generation confirmatory tests for detection of antibody to hepatitis C virus

Characterization of mimotopes mimicking an immunodominant conformational epitope on the hepatitis C virus NS3 helicase

The hepatitis C virus (HCV) nonstructural 3 (NS3) protein is composed of an amino terminal protease and a carboxyl terminal RNA helicase. NS3 contains major antigenic epitopes. The antibody response to NS3 appears early in the course of infection and is focused on the helicase region. However, this response cannot be defined by short synthetic peptides indicating the recognition of conformation-dependent epitopes. In this study, we have screened a dodecapeptide library displayed on phage with anti-NS3 mouse monoclonal antibodies (mAbs) that compete with each other and human anti-HCV NS3 positive sera. Two peptides (mimotopes) were selected that appeared to mimic an immunodominant epitope since they were recognized specifically by the different anti-NS3 mAbs of the study and by human sera from HCV infected patients. Homology search between the two mimotopes and the NS3 sequence showed that one of the two peptides shared amino acid similarities with NS3 at residues 1396-1398 on a very accessible loop as visualized on the three-dimensional structure of the helicase domain whereas the other one had two amino acids similar to nearby residues 1376 and 1378. Reproduced as synthetic dodecapeptides, the two mimotopes were recognized specifically by 19 and 22, respectively, out of 49 sera from HCV infected patients. These mimotopes allowed also the detection of anti-NS3 antibodies in sera of HCV patients at the seroconversion stage. These results suggest that the two NS3 mimotopes are potential tools for the diagnosis of HCV infection.

Sensitivity and specificity of third-generation hepatitis C virus antibody detection assays: an analysis of the literature

This study assessed the sensitivity and specificity of third-generation serological hepatitis C diagnostic tests from an analysis of the literature. The literature analysis was run using criteria from McMaster University for the assessment of diagnostic tests. The selected studies were grouped according to the type of population at high and low risk for hepatitis C virus (HCV) infection and to the type of reference test. The homogeneity of the sensitivity and the specificity was tested in each group using a Fisher's exact test. Of 132 studies, 10 were selected. When the estimates were homogeneous, summary point estimates and confidence intervals were computed; when the estimates were heterogeneous, subgroup analysis was performed. The sensitivity of third-generation enzyme-linked immunosorbent assay (ELISA3) was estimated at 98.9% (95% CI: 94-100%) in patients with chronic liver disease and at 97.2% (95% CI: 92-99%) in panels of sera. ELISA3 specificity was found at 100% in patients with chronic liver disease. The sensitivity of the third generation recombinant immunoblot assay (RIBA3) was assessed at 78.8% (95% CI: 65-89%) in haemodialysed patients. This analysis provides evidence for the good sensitivity and specificity of ELISA3 assays particularly in high risk patient groups and confirms their use for screening in these populations. Further studies are needed to assess properly RIBA3 in general population and in risk patients.

Development of low cost peptide-based anti-hepatitis C virus screening and confirmatory assays: comparison with commercially available tests

Screening and confirmatory low cost reagent tests have been developed for detection of anti-hepatitis C virus (HCV). Assays are based on the use of specific synthetic peptides from several structural and non-structural viral proteins. The efficacy of the screening anti-HCV EIA-Spep assay was compared with both Abbott EIA 2.0 (Abbott Laboratories, North Chicago, IL) and Ortho EIA 2.0 (Ortho Diagnostic Systems, Raritan, NJ) anti-HCV detection kits and the confirmatory EIA-Cpep assay was compared with the Abbott Matrix anti-HCV confirmation test. In the EIA-Spep, a pool of 3 peptides was added to each well of a microtiter plate. In EIA-Cpep, each well was separately coated with 1 of 4 peptides and 1 recombinant protein. A total of 867 blood donor samples from Costa Rica tested simultaneously with the 3 screening assays yielded the same specificity and negative predictive values of > or =99.9% and 100%, respectively. A comparative study on voluntary blood donor samples from Honduras, Nicaragua, and El Salvador using the 2 anti-HCV confirmatory assays revealed different patterns that are 46% positive, 24% indeterminate, and 30% negative with the EIA-Cpep assay vs. 31% positive, 48% indeterminate, and 21% negative with the Matrix assay. A study of 71 patient samples from Costa Rica showed a higher correlation between initially reactive samples when analyzed by the Abbott and Ortho kits, than when the assay results were compared between the Abbott and EIA-Spep kits; the latter detected 7 and 15 non-reactive samples, respectively. These results could reflect the use of a similar antigen source for the 2 commercial assays. The presence of HCV RNA in a group of 29 samples analyzed was related to the simultaneous reactivity in all 3 screening assays. None of the discordant samples had detectable levels of HCV RNA. Economic difficulties for health care services in the developing countries of Central America have prevented implementation of routine anti-HCV blood donor screening tests. This is likely to be the primary reason for uncontrolled dissemination of HCV, and the lack of identification of potential high risk groups. Alternative low cost reagents developed locally as described in this article could be a useful tool in the control of HCV spread throughout the developing world.

Supplementary anti-hepatitis C virus (HCV) testing with 2nd and 3rd generation recombinant immunoblot assay and matrix applied to enzyme immunoassay positive sera and comparison with HCV-RNA detection

A series of 118 serum samples tested positive in the anti-hepatitis C virus (HCV) 2nd-generation enzyme immunoassay (EIA-2), and indeterminate (93 samples) or negative (25 samples) in the supplementary 2nd-generation recombinant immunoblot assay (RIBA-2). These sera were further evaluated by three additional tests: 3rd-generation RIBA (RIBA-3), MATRIX, and AMPLICOR HCV-PCR. For the 93 RIBA-2 indeterminate serum samples, the results of the immunoassays had a concordance of 69%. Twenty-one and 34 samples remained anti-HCV indeterminate in the RIBA-3 test and the MATRIX, respectively. Among the 25 RIBA-2-negative samples, only seven samples remained anti-HCV negative, while five samples tested anti-HCV positive in both RIBA-3 and MATRIX. The reactivity of the RIBA-3 antigen NS5 was not crucial for the result of any sample. Positive to negative contradictions between the results of MATRIX and RIBA-3 were never observed. Altogether, the MATRIX tested a significantly lower number of samples anti-HCV negative than did the RIBA-3. HCV RNA was detectable in 54/93 RIBA-2 indeterminate and 7/25 RIBA-2 negative samples. High percentages of PCR positive results among RIBA-3-indeterminate and among MATRIX-indeterminate samples indicate an increased possibility of detecting HCV RNA if at least one antigen is reactive. The type of antigen, the pattern of antigen reactivity, or the level of reactivity had no prognostic value in predicting the presence of HCV RNA. Our findings show the necessity of being cautious in the interpretation of RIBA-2-negative results.

Evaluation of a pooling method for routine anti-HCV screening of blood donors to lower the cost burden on blood banks in countries under development

A pooling system was developed for use in anti-HCV screening of voluntary blood donors at the local Central American Red Cross blood banks, in Nicaragua, El Salvador and Honduras. The commercially available second generation anti-HCV screening kit from Abbott Laboratories (North Chicago, IL) was used with a modification in the initial serum dilution procedure. Pools of five sera were selected for routine screening, based on comparative studies of individual samples and of pools with different sample sizes. During the years 1993 and 1994 a total of 89, 148 voluntary blood donors were screened and a positive prevalence rate of 0.35% was established. Of the initially positive samples, 54% confirmed positive, 30% were indeterminate and 16% were negative using the Abbott Matrix test. Significant differences of positive screening prevalence rates were found in the three countries, with average values of 0.50%, 0.23% and 0.08%, respectively, in Nicaragua, El Salvador and Honduras. These initially positive samples also showed a different confirmatory pattern with a positive rate of 64% in Nicaragua, in contrast to 20% in El Salvador. Only a few samples were available for RT-PCR amplification of HCV-RNA; however, this highly sensitive method did not appear to be more helpful than serology in confirming the HCV donor status. Overall, the data obtained indicate a fluctuation of HCV prevalence in voluntary blood donors among the three Central American countries. Further, differences were found in the percentages of initially screened positives and confirmation patterns. This information appears useful for establishing criteria in future screening policies. Thus, we suggest that the use of pooling for anti-HCV screening is beneficial in countries under development, since there are potential cost savings, as well as benefits in establishment of initial prevalence rates.