Current and future assays for identifying recent HIV infections at the population level

The precise diagnosis of recent human immunodeficiency virus (HIV) infection is crucial for estimating HIV incidence, defined as the number of new infections in a population, per person at risk, during a specified time period. Incidence assessment is considered to be a tool for surveillance, public health and research. Differentiating recent from long-term HIV infections is possible thanks to the evaluation of HIV-specific immune response development or viral markers measurement. Several methods that enable the recognition of recent HIV-1 infection with the use of a single blood specimen have been developed, and their value for use in population level studies has been demonstrated. However, they are still inadequate due to a variable window period and false recent rates among HIV clades and across populations. Application of these assays at an individual level is far more questionable because of person-to-person variability in the antibody response and the course of HIV infection, and because of the prospective regulatory approval requirements. In this article we review the principles and the limitations of the currently available major laboratory techniques that allow detection of recent HIV infection. The assays based on the alteration of serological parameters, as well as the newest method based on an increase of HIV genetic diversity with the progress of infection, are described.