Reduction of the risk of transfusion-transmitted human immunodeficiency virus (HIV) infection by using an HIV antigen/antibody combination assay in blood donation screening in Cameroon.

BACKGROUND: Improving blood safety without introducing nucleic acid testing in blood screening may be possible using antigen/antibody (Ag/Ab) combination assays, especially in resource-poor countries. STUDY DESIGN AND METHODS: To evaluate the potential reduction of human immunodeficiency virus (HIV)-transmitted infection using such an assay, a study was carried out aimed to compare the routine strategy for blood screening (S1), combining a rapid test (Determine HIV-1/-2, Inverness) and an enzyme immunoassay (human HIV-1/-2, Human Diagnostic) with an HIV Ag/Ab assay (S2, Genscreen ULTRA HIV Ag-Ab, Bio-Rad) in 2000 blood donations tested in Cameroon. Western blot and HIV RNA polymerase chain reaction were used to confirm the infection in reactive donors, and genotype was determined in HIV RNA-positive samples. RESULTS: Of the 2000 donors, 3.1% were positive with S1 and 4.3% with S2. Of the 97 samples positive with S1 and/or S2 tested for confirmation, 54.7% were positive, 38.1% indeterminate, and 7.2% negative. There were significant differences between S1 and S2 in terms of sensitivity (S1, 79.2%; S2, 100%), irrespective of the genotype, and in specificity (S1, 99.0; S2, 98.3%). The most frequent genotype (49%) was CRF02_AG. CONCLUSIONS: A testing strategy using Genscreen ULTRA HIV Ag/Ab could prevent 55 HIV transmissions per 10,000 donations. However, this would be at a cost of discarding 170 per 10,000 negative donations that would test false positive, showing that the implementation of new techniques in blood screening need an optimization before routine use. Using confirmatory assays, HIV Ab prevalence in blood donors in Cameroon was estimated at 2.65%.

The variable sensitivity of HIV Ag/Ab combination assays in the detection of p24Ag according to genotype could compromise the diagnosis of early HIV infection.

BACKGROUND: In France, HIV infection diagnosis was modified by a decree, published in 2010, that requires the use of HIV Ag/Ab assays able to detect at least 2 IU/ml of p24Ag. This measure raises the concern of the capacity of these assays to equally detect all HIV variants. OBJECTIVES: To assess the performance of HIV Ag/Ab assays for the detection of p24Ag from diverse HIV isolates. STUDY DESIGN: Ten HIV Ag/Ab assays were compared using two p24Ag reference standards, 297 samples from 99 HIV-1 and HIV-2 cell-culture derived isolates including various subtypes and groups, and 9 native specimens from subjects with primary HIV infection. RESULTS: The p24Ag limit of detection (LOD) ranged from 0.505 IU/ml to 1.90 1 IU/ml and, from 11.9 pg/ml to 33.5 pg/ml when using WHO and French national standards, respectively. The overall percentage of positive samples ranged from 26.8% to 74.5%. Five assays failed to detect all dilutions of at least one group M subtype, three missed all group O and six all the group P samples. Three assays were able to detect 2-10 of the 30 HIV-2 samples. The distribution of LODs for each group M isolate showed a wide dispersion between the assays. Percentage of isolates detected at a p24Ag level less than 2 IU/ml varied from 22% to 98.7%. CONCLUSION: This study demonstrated that, even though their analytical sensitivity fulfills the requirements, many of HIV Ag/Ab assays could fail to detect HIV primary infection due to HIV-1 non-B, non-M and HIV-2 strains.