title: Development and Evaluation of a Modified Fourth-Generation Human Immunodeficiency Virus Enzyme Immunoassay for Cross-Sectional Incidence Estimation in Clade B Populations.
abstract: Accurate methods for cross-sectional incidence estimation are needed for HIV surveillance and prevention research. We developed an avidity assay based on the fourth-generation Genetic Systems HIV Combo Ag/Ab EIA (Bio-Rad Combo assay) and evaluated its performance.
  
  
  
  The Bio-Rad Combo assay was modified incubating samples with and without 0.025 M diethylamine (DEA). The avidity index (AI) was calculated as the ratio of the DEA-treated to untreated result for a specific sample. We analyzed 2,140 samples from 808 individuals from the United States with known duration of HIV infection. The mean duration of recent infection (MDRI) and the false-recent rate (FRR, fraction of samples from individuals known to be infected >2 years misclassified as recent) were calculated for AI cutoffs of 20%-90% for the avidity assay alone and in combination with a viral load assay (VL, limit of detection 400 copies/ml). Factors associated with misclassification of samples collected ≥2 years after infections were also evaluated.
  
  
  
  The MDRI for the Bio-Rad Combo Avidity assay ranged from 50 days using an AI cutoff of 20% to 276 days using an AI cutoff of 90%; the FRR ranged from 0% to 9%. When samples with a VL <400 copies/ml were classified as nonrecent, the FRRs were reduced approximately twofold and the MDRI estimates were reduced by ∼20%. An AI cutoff of 50% provided an MDRI of 135 days with an FRR of 2.1%. All samples from elite suppressors had an AI >80%. In adjusted analysis, viral suppression and low CD4 cell count were significantly associated with misclassification among individuals infected >2 years.
  
  
  
  This modified Bio-Rad Combo Avidity assay may be a useful tool for cross-sectional HIV incidence estimation. Further research is needed to evaluate use of this assay in combination with other assays to accurately estimate population-level HIV incidence.
authors.affiliation: 1 Laboratory of Immunoregulation, Division of Intramural Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health , Baltimore, Maryland.
authors.forename: Allison R
authors.initials: AR
authors.lastname: Kirkpatrick
authors.affiliation: 1 Laboratory of Immunoregulation, Division of Intramural Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health , Baltimore, Maryland.
authors.forename: Eshan U
authors.initials: EU
authors.lastname: Patel
authors.affiliation: 2 Department of Medicine, University of Washington , Seattle, Washington.
authors.forename: Connie L
authors.initials: CL
authors.lastname: Celum
authors.affiliation: 3 Department of Medicine, Johns Hopkins University School of Medicine , Baltimore, Maryland.
authors.forename: Richard D
authors.initials: RD
authors.lastname: Moore
authors.affiliation: 3 Department of Medicine, Johns Hopkins University School of Medicine , Baltimore, Maryland.
authors.forename: Joel N
authors.initials: JN
authors.lastname: Blankson
authors.affiliation: 4 Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health , Baltimore, Maryland.
authors.forename: Shruti H
authors.initials: SH
authors.lastname: Mehta
authors.affiliation: 4 Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health , Baltimore, Maryland.
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Kirk
authors.affiliation: 5 Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health , Baltimore, Maryland.
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Margolick
authors.affiliation: 1 Laboratory of Immunoregulation, Division of Intramural Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health , Baltimore, Maryland.|3 Department of Medicine, Johns Hopkins University School of Medicine , Baltimore, Maryland.
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Quinn
authors.affiliation: 6 Department of Pathology, Johns Hopkins University School of Medicine , Baltimore, Maryland.
authors.forename: Susan H
authors.initials: SH
authors.lastname: Eshleman
authors.affiliation: 1 Laboratory of Immunoregulation, Division of Intramural Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health , Baltimore, Maryland.|3 Department of Medicine, Johns Hopkins University School of Medicine , Baltimore, Maryland.
authors.forename: Oliver
authors.initials: O
authors.lastname: Laeyendecker
mesh_terms: D000328:Adult; D000915:Antibody Affinity; D000936:Antigen-Antibody Complex / Q000032:analysis* / Q000096:biosynthesis; D018791:CD4 Lymphocyte Count; D003430:Cross-Sectional Studies; D004048:Diethylamines / Q000737:chemistry; D005260:Female; D015483:HIV Antibodies / Q000097:blood* / Q000737:chemistry; D015488:HIV Antigens / Q000097:blood* / Q000737:chemistry; D015658:HIV Infections / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology / Q000821:virology; D015497:HIV-1 / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D006801:Humans; D007124:Immunoenzyme Techniques / Q000592:standards*; D015994:Incidence; D008297:Male; D008875:Middle Aged; D014481:United States / Q000453:epidemiology; D019562:Viral Load / Q000276:immunology
chemical_list: D000936:Antigen-Antibody Complex; D004048:Diethylamines; D015483:HIV Antibodies; D015488:HIV Antigens; C034281:diethylamine