Application of the BED capture enzyme immunoassay for HIV incidence estimation among female sex workers in Kaiyuan City, China, 2006-2007

Objective: To estimate HIV incidence among female sex workers (FSWs) by serial cross-sectional surveys and IgG-capture BED-enzyme immunoassay (BED-CEIA). Methods: We conducted three cross-sectional surveys, 6 months apart, among all consenting FSWs in Kaiyuan City, China. HIV antibody-positive samples were also tested by BED-CEIA. Results: Among 1412 unique participants, 475 tested HIV-negative and attended >1 survey (longitudinal cohort). Compared to 786 HIV-negative FSWs who only participated once, the longitudinal cohort reported more illicit drug use (10.9% vs. 7.4%, p = 0.03), injected drugs more often in the previous 3 months (8.8% vs. 5.3%, p = 0.02), and had more positive urine opiate tests (13.7% vs. 8.9%, p = 0.008). Four participants in the longitudinal cohort seroconverted over the year, with an overall incidence of 1.1/100 person-years (95% confidence interval (CI) 0.3-2.8). Crude BED-CEIA incidence was 3.4/100 person-years (95% CI 2.3-4.4) with adjusted rates similar to the cohort incidence: McDougal, 1.5/100 person-years (95% CI 1.0-2.0); Hargrove, 1.6/100 person-years (95% CI 1.1-2.1). The BED-CEIA false-positive rate was 4.4% (10/229) among samples from FSWs known to be infected ≥365 days. Conclusions: Although limited by power, this study provides additional data towards validating BED-CEIA in China. If confirmed by other studies, BED-CEIA will be a useful tool to estimate HIV incidence rates and trends.