title: Performance of the fourth-generation Bio-Rad GS HIV Combo Ag/Ab enzyme immunoassay for diagnosis of HIV infection in Southern Africa.
abstract: BACKGROUND
  Fourth-generation HIV assays detect both antigen and antibody, facilitating detection of acute/early HIV infection. The Bio-Rad GS HIV Combo Ag/Ab assay (Bio-Rad Combo) is an enzyme immunoassay that simultaneously detects HIV p24 antigen and antibodies to HIV-1 and HIV-2 in serum or plasma.
  
  
  OBJECTIVE
  To evaluate the performance of the Bio-Rad Combo assay for detection of HIV infection in adults from Southern Africa.
  
  
  METHODS
  Samples were obtained from adults in Soweto and Vulindlela, South Africa and Dar es Salaam, Tanzania (300 HIV-positive samples; 300 HIV-negative samples; 12 samples from individuals previously classified as having acute/early HIV infection). The samples were tested with the Bio-Rad Combo assay. Additional testing was performed to characterize the 12 acute/early samples.
  
  
  RESULTS
  All 300 HIV-positive samples were reactive using the Bio-Rad Combo assay; false positive test results were obtained for 10 (3.3%) of the HIV-negative samples (sensitivity: 100%, 95% confidence interval [CI]: 98.8-100%); specificity: 96.7%, 95% CI: 94.0-98.4%). The assay detected 10 of the 12 infections classified as acute/early. The two infections that were not detected had viral loads<400 copies/mL; one of those samples contained antiretroviral drugs consistent with antiretroviral therapy.
  
  
  CONCLUSIONS
  The Bio-Rad Combo assay correctly classified the majority of study specimens. The specificity reported here may be higher than that seen in other settings, since HIV-negative samples were pre-screened using a different fourth-generation test. The assay also had high sensitivity for detection of acute/early infection. False-negative test results may be obtained in individuals who are virally suppressed.
authors.affiliation: Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: Estelle
authors.initials: E
authors.lastname: Piwowar-Manning
authors.affiliation: Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: Jessica M
authors.initials: JM
authors.lastname: Fogel
authors.affiliation: Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Richardson
authors.affiliation: Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: Shauna
authors.initials: S
authors.lastname: Wolf
authors.affiliation: Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: William
authors.initials: W
authors.lastname: Clarke
authors.affiliation: Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Marzinke
authors.affiliation: Program in Global Health, University of California at Los Angeles, Los Angeles, CA, USA.
authors.forename: Agnès
authors.initials: A
authors.lastname: Fiamma
authors.affiliation: Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center, Seattle, WA, USA; Department of Global Health, University of Washington, Seattle, WA, USA.
authors.forename: Deborah
authors.initials: D
authors.lastname: Donnell
authors.affiliation: Department of Probability and Statistics, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic.
authors.forename: Michal
authors.initials: M
authors.lastname: Kulich
authors.affiliation: Muhimbili University of Health and Allied Sciences, Muhimbili University Teaching Hospital, Dar es Salaam, Tanzania.
authors.forename: Jessie K K
authors.initials: JK
authors.lastname: Mbwambo
authors.affiliation: DST-NRF Centre of Excellence in Human Development, Universities of the Witwatersrand and KwaZulu-Natal, South Africa; Human Sciences Research Council, Durban, South Africa.
authors.forename: Linda
authors.initials: L
authors.lastname: Richter
authors.affiliation: Perinatal HIV Research Unit, Chris Hani Baragwanath Hospital, University of the Witwatersrand, Johannesburg, South Africa; South African Medical Research Council, Cape Town, South Africa.
authors.forename: Glenda
authors.initials: G
authors.lastname: Gray
authors.affiliation: Department of Psychiatry and Behavioral Sciences, The Medical University of South Carolina, Charleston, SC, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Sweat
authors.affiliation: Center for World Health, David Geffen School of Medicine and UCLA Health, Los Angeles, CA, USA.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Coates
authors.affiliation: Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD, USA. Electronic address: seshlem@jhmi.edu.
authors.forename: Susan H
authors.initials: SH
authors.lastname: Eshleman
mesh_terms: D000353:Africa, Southern; D006678:HIV / Q000276:immunology*; D015483:HIV Antibodies / Q000276:immunology; D015488:HIV Antigens / Q000276:immunology; D016655:HIV Core Protein p24 / Q000276:immunology; D015658:HIV Infections / Q000175:diagnosis* / Q000276:immunology / Q000821:virology; D015497:HIV-1 / Q000276:immunology; D015498:HIV-2 / Q000276:immunology; D006801:Humans; D007124:Immunoenzyme Techniques / Q000379:methods / Q000592:standards; D011933:Reagent Kits, Diagnostic / Q000592:standards; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D015483:HIV Antibodies; D015488:HIV Antigens; D016655:HIV Core Protein p24; D011933:Reagent Kits, Diagnostic
keywords: Africa; Diagnosis; Enzyme immunoassay; Fourth-generation; HIV