RÉSUMÉ
Laboratory tests that can distinguish recent from long-term HIV infection are used to estimate HIV incidence in a population, but can potentially misclassify a proportion of long-term HIV infections as recent. Correct application of an assay requires determination of the proportion false recents (PFRs) as part of the assay characterization and for calculating HIV incidence in a local population using a HIV incidence assay. From April 2009 to December 2010, blood specimens were collected from HIV-infected individuals attending nine outpatient clinics (OPCs) in Vietnam (four from northern and five from southern Vietnam). Participants were living with HIV for ≥1 year and reported no antiretroviral (ARV) drug treatment. Basic demographic data and clinical information were collected. Specimens were tested with the BED capture enzyme immunoassay (BED-CEIA) and the Limiting-antigen (LAg)-Avidity EIA. PFR was estimated by dividing the number of specimens classified as recent by the total number of specimens; 95% confidence intervals (CI) were calculated. Specimens that tested recent had viral load testing performed. Among 1,813 specimens (north, n = 942 and south, n = 871), the LAg-Avidity EIA PFR was 1.7% (CI: 1.2-2.4) and differed by region [north 2.7% (CI: 1.8-3.9) versus south 0.7% (CI: 0.3-1.5); p = .002]. The BED-CEIA PFR was 2.3% (CI: 1.7-3.0) and varied by region [north 3.4% (CI: 2.4-4.7) versus south 1.0% (CI: 0.5-1.2), p < .001]. Excluding specimens with an undetectable VL, the LAg-Avidity EIA PFR was 1.2% (CI: 0.8-1.9) and the BED-CEIA PFR was 1.7% (CI: 1.2-2.4). The LAg-Avidity EIA PFR was lower than the BED-CEIA PFR. After excluding specimens with an undetectable VL, the PFR for both assays was similar. A low PFR should facilitate the implementation of the LAg-Avidity EIA for cross-sectional incidence estimates in Vietnam.