Hiv Incidence In South African Blood Donors From 2012 To 2016: A Comparison Of Estimation Methods

Background Measuring incidence is important for monitoring and maintaining the safety of the blood supply. Blood collected from repeat-donors has provided the opportunity to follow blood donors over time and has been used to estimate the incidence of viral infections. These incidence estimates have been extrapolated to first-time donors using the ratio of NAT yield cases in first-time versus repeat-donors. We describe a model to estimate incidence in first-time donors using the limiting antigen (LAg) avidity assay and compare its results with those from established models.Methods HIV-positive first-time donations were tested for recency using the LAg assay. Three models were compared; incidence estimated for (1) first-time donors using LAg avidity, (2) first-time and repeat-donors separately using the NAT yield window period (WP) model and (3) repeat-donors using the incidence/WP model.Results HIV incidence in first-time donors was estimated at 3.32 (CI 3.11, 3.55) and 3.81 (CI 3.07, 4.73) per 1000 PY using the LAg assay and NAT yield WP models, respectively. Incidence in repeat-donors was between 2.0- and 2.5-fold lower than in first-time donors estimated at 1.56 (CI 1.37, 1.77) and 1.94 (CI 1.86-2-01) per 1000 PY using the NAT yield/WP and incidence/WP models, respectively.Conclusion Testing HIV-positive donations using the LAg assay provides a reliable method to estimate incidence in first-time donors for countries that collect the majority of blood from first-time donors and do not screen with NAT.