title: The accuracy of an alternative confirmatory strategy for detection of antibodies to HIV-1: experience from a regional laboratory in Kagera, Tanzania.
abstract: BACKGROUND
  Constant improvement of HIV tests often results in withdrawal of poorer quality tests by the manufacturing companies. It is thus often necessary to evaluate new HIV testing kits and modify the existing testing strategies.
  
  
  OBJECTIVE
  To evaluate an alternative HIV antibody testing strategy which involves consecutive testing of sera by two enzyme-linked immunosorbent assays (ELISA), which both are recombinant antigen-based but utilise different test principles, followed by re-testing of sera giving discordant results.
  
  
  METHODS
  Sera (n = 1558) from a cross-sectional study of the HIV-1 seroprevalence in the Kagera region of Tanzania were tested using two ELISAs in parallel: Enzygnost anti-HIV-1/2 plus and Wellcozyme HIV-1 recombinant. Western blot analysis was done on all concordantly reactive and repeatedly discordant reactive samples as well as on 10% of concordantly ELISA negative sera.
  
  
  RESULTS
  Two hundred and four sera (13.1%) were confirmed HIV-1-antibody positive. Both ELISAs had a sensitivity of 100%. The specificities of the ELISAs 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 sera was concordantly false positive in both ELISAs. The mean ratio of the optical 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 HIV-1-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 involving the use of a recombinant antigen-based sandwich ELISA (Enzygnost) followed by a recombinant antigen-based competitive ELISA (Wellcozyme) showed that it had a sensitivity and specificity of 100%.
authors.affiliation: Department of Microbiology, Muhimbili University College of Health Sciences, Dar es Salaam, Tanzania.
authors.forename: W
authors.initials: W
authors.lastname: Urassa
authors.forename: K
authors.initials: K
authors.lastname: Godoy
authors.forename: J
authors.initials: J
authors.lastname: Killewo
authors.forename: G
authors.initials: G
authors.lastname: Kwesigabo
authors.forename: A
authors.initials: A
authors.lastname: Mbakileki
authors.forename: F
authors.initials: F
authors.lastname: Mhalu
authors.forename: G
authors.initials: G
authors.lastname: Biberfeld
mesh_terms: D015492:AIDS Serodiagnosis / Q000379:methods*; D003430:Cross-Sectional Studies; D004797:Enzyme-Linked Immunosorbent Assay; D005189:False Positive Reactions; D005260:Female; D015483:HIV Antibodies / Q000097:blood*; D015488:HIV Antigens; D006679:HIV Seropositivity / Q000097:blood* / Q000175:diagnosis; D015497:HIV-1 / Q000276:immunology*; D015498:HIV-2 / Q000276:immunology; D006801:Humans; D007106:Immune Sera; D008297:Male; D011933:Reagent Kits, Diagnostic; D011994:Recombinant Proteins; D012680:Sensitivity and Specificity; D013636:Tanzania
chemical_list: D015483:HIV Antibodies; D015488:HIV Antigens; D007106:Immune Sera; D011933:Reagent Kits, Diagnostic; D011994:Recombinant Proteins