title: Performance of a fourth-generation HIV screening assay and an alternative HIV diagnostic testing algorithm.
abstract: OBJECTIVE
  We evaluated the performance of the GS fourth-generation antigen/antibody assay and compared Centers for Disease Control and Prevention's (CDC's) proposed alternative algorithm [repeatedly reactive fourth-generation immunoassay followed by an HIV-1/HIV-2 differentiation immunoassay and, if needed, nucleic acid test (NAT)] with the current algorithm (repeatedly reactive third-generation immunoassay followed by HIV-1 western blot).
  
  
  METHODS
  A convenience sample of the following four specimen sets was acquired: 10 014 from insurance applicants, 493 known western blot-positive, 20 known western blot-indeterminate specimens, and 230 specimens from 26 HIV-1 seroconverters.
  
  
  METHODS
  Specimens were tested with the GS third-generation and fourth-generation immunoassays, the Multispot HIV-1/HIV-2 differentiation immunoassay, NAT, and western blot. We applied the two algorithms using these results.
  
  
  RESULTS
  Among insurance specimens, 13 (0.13%) specimens were immunoassay repeatedly reactive: two were HIV-positive (repeatedly reactive by third-generation and fourth-generation immunoassays, and western blot and Multispot positive); two third-generation repeatedly reactive and nine fourth-generation repeatedly reactive specimens were false-positive. Third-generation and fourth-generation specificities were 99.98% [95% confidence interval (CI) 99.93-100%] and 99.91% (95% CI 99.84-99.96%), respectively.All HIV-1 western blot-positive specimens were repeatedly reactive by third-generation and fourth-generation immunoassays. By Multispot, 491 (99.6%) were HIV-1-positive and two (0.4%) were HIV-2-positive.Only eight (40%) western blot-indeterminate specimens were fourth-generation repeatedly reactive: six were Multispot and NAT-negative and two were Multispot HIV-1-positive but NAT-negative.The alternative algorithm correctly classified as positive 102 seroconverter specimens with the third-generation immunoassay and 130 with the fourth-generation immunoassay compared with 56 using the western blot with either immunoassay.
  
  
  CONCLUSIONS
  The alternative testing algorithm improved early infection sensitivity and identified HIV-2 infections. Two potential false-positive algorithm results occurred with western blot-indeterminate specimens.
authors.affiliation: Division of HIV/AIDS Prevention, National Center for HIV, Hepatitis, STD and TB Prevention, Centers for Disease Control and Prevention, Atlanta, GA, USA. snasrullah@cdc.gov
authors.forename: Muazzam
authors.initials: M
authors.lastname: Nasrullah
authors.forename: Laura G
authors.initials: LG
authors.lastname: Wesolowski
authors.forename: William A
authors.initials: WA
authors.lastname: Meyer
authors.forename: S Michele
authors.initials: SM
authors.lastname: Owen
authors.forename: Silvina
authors.initials: S
authors.lastname: Masciotra
authors.forename: Craig
authors.initials: C
authors.lastname: Vorwald
authors.forename: William J
authors.initials: WJ
authors.lastname: Becker
authors.forename: Bernard M
authors.initials: BM
authors.lastname: Branson
mesh_terms: D000465:Algorithms; D015153:Blotting, Western / Q000379:methods; D003955:Diagnostic Tests, Routine / Q000379:methods; D015483:HIV Antibodies / Q000276:immunology; D015658:HIV Infections / Q000175:diagnosis* / Q000276:immunology; D015497:HIV-1 / Q000276:immunology*; D015498:HIV-2 / Q000276:immunology*; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D008403:Mass Screening / Q000379:methods; D021141:Nucleic Acid Amplification Techniques / Q000379:methods; D012680:Sensitivity and Specificity
chemical_list: D015483:HIV Antibodies