Evaluation of commercially available assays for antibodies to HIV-1 in serum obtained from South African patients infected with HIV-1 subtypes B, C, and D.

Between 1984 and 1990, virus was routinely isolated and serum collected from patients diagnosed at hospitals in the Western Cape as suffering from AIDS or AIDS-related conditions (ARC). From these, 17 virus strains were selected at random for sequencing and molecular characterisation of the env gene. The strains were previously characterised as belonging to HIV-1 subtypes B, C and D. The purpose of the present study was to evaluate retrospectively the serological diagnosis of HIV-1 in these 17 South African patients. Thirteen anti-HIV screening assays, including 7 rapid/simple test devices (RTDs), 4 enzyme-linked immunosorbent assays (EIAs) and 2 Western immunoblot assays were evaluated. Using commercial EIAs, 16 serum samples were HIV antibody-positive and these results were confirmed by Western immunoblot analysis. Serum from one terminal AIDS patient was found negative with all the serological tests. Some RTDs gave false negative antibody reactions on specimens from patients infected with subtype D strains. To investigate the false negative antibody reactions, the polymerase chain reaction (PCR) was used to amplify, clone and sequence proviral DNA from the immunodominant gp41 region from 7 of the HIV-1 strains. Two patients, both subtype D strains (D214 and D482) with false negative results in the RTDs, showed a significant amino acid substitution, i.e., substitution of a histidine residue for leucine at env position 607. It was concluded that although there were false negative RTD reactions on patients with HIV-1 subtype D strains, the commercial EIAs tested are sensitive and are able to detect patients infected with HIV-1 subtypes B, C and D that are present in South Africa.