Repeat screening for HIV: when to test and why.

This paper presents models for repeat HIV screening under conditions of constant low HIV incidence. The models reveal a direct link between the prevalence of undetected HIV infection and the screening interval between repeat HIV tests. We show how to select screening intervals that either achieve a given HIV prevalence level, or optimally balance the cost of repeat HIV testing against the cost of HIV infection. Alternatively, given an existing repeat screening program, the model implies that cost of infection for which the given screening interval is optimal. The method also suggests how to select an HIV testing technology. The models are applied to existing repeat testing programs in the U.S. Army and among legal commercial sex workers in the state of Nevada in the Far West of the United States.