HIV Incidence

WHO P Virot

HIV incidence is the number of new HIV infections in a population during a certain time period. The determination of HIV incidence in a population is important to:

• monitor the epidemic
• improve the targeting of populations for interventions
• and to evaluate the effectiveness of HIV prevention and treatment programs.

This is especially important in low and middle income countries that continue to bear a disproportionate share of the global burden of HIV/AIDS. In addition, the identification of newly infected persons will allow for interventions to reduce the risk of HIV transmission.

The challenge of measuring HIV incidence

Determining the best strategy for measuring incidence remains a challenge. Traditional HIV surveillance methods have used changes in measures of prevalence to estimate HIV incidence rates, but this approach requires multiple rounds of surveillance over many years in the same population groups. The prospective follow-up of a cohort of HIV-negative persons provides a direct measure of HIV incidence; however such studies are challenging, expensive, not sustainable in resource-limited settings and raise ethical issues. Furthermore, the enrollment of persons into a cohort study often leads to behaviour changes that result in a lower observed HIV incidence than in the broader population of interest.

To address these challenges, several research groups have made efforts to develop assays aimed at identifying people with recent infection (for example, less than six months). However, a recognized and urgent need exists to validate the performance of current assays and to develop new and improved HIV incidence assays. The World Health Organization has established a Technical HIV Incidence Assay Working Group (HIVIWG) to provide technical guidance and to advance efforts in this area of work.