The accuracy of an alternative confirmatory strategy for detection of antibodies to HIV-1: experience from a regional laboratory in Kagera, Tanzania

Background: Constant improvement of HIV tests often results in withdrawal o f poorer quality tests by the manufacturing companies. It is thus often nec essary to evaluate new HIV testing kits and modify the existing testing str ategies. Objectives: To evaluate an alternative HIV antibody testing strategy which involves consecutive testing of sera by two enzyme-linked immunosorbent ass ays (ELISA), which both are recombinant antigen-based but utilise different test principles, followed by re-testing of sera giving discordant results. Study design: Sera (n = 1558) from a cross-sectional study of the HIV-I ser oprevalence in the Kagera region of Tanzania were tested using two ELISAs i n parallel: Enzygnost anti-HIV-1/2 plus and Wellcozyme HIV-1 recombinant. W estern blot analysis was done on all concordantly reactive and repeatedly d iscordant reactive samples as well as on 10% of concordantly ELISA negative sera. Results: Two hundred and four sera (13.1%) were confirmed HIV-l-antibody po sitive. Both ELISAs had a sensitivity of 100%. The specificities of the ELI SAs at initial and repeated testing were 99.8 and 99.9%, respectively, for Enzygnost and 97.7 and 99.5%, respectively, for Wellcozyme. None of the ser a was concordantly false positive in both ELISAs. The mean ratio of the opt ical density of a sample to the cut off value of the test run (OD/CO ratio) was lower for samples giving false positive reactions than for confirmed H IV-l-antibody-positive samples. It is therefore important to interpret with caution HIV antibody ELISA test results on samples giving low OD/CO ratios . None of 10% of randomly selected concordantly ELISA negative sera gave a positive Western blot reaction. Conclusions: This field evaluation of an HIV antibody testing strategy invo lving the use of a recombinant antigen-based sandwich ELISA (Enzygnost) fol lowed by a recombinant antigen-based competitive ELISA (Well cozyme) showed that it had a sensitivity and specificity of 100%. (C) 1999 Elsevier Scien ce B.V. All rights reserved.