Estimating the population need for preexposure prophylaxis for HIV in the United States.

Preexposure prophylaxis (PrEP) is highly effective in preventing HIV infections and is recommended for people without HIV who are at ongoing risk of HIV acquisition. In 2019, the U.S. launched the "Ending the HIV Epidemic in the U.S." initiative, which aims to reduce by 90 % the number of annual new HIV infections. To monitor progress towards this goal, several national indicators have been established, one of which is PrEP coverage. Several ways to monitor PrEP use have been developed, each with its own advantages and disadvantages. We developed a method to estimate PrEP "need" in the U.S. that could be used as a denominator to estimate PrEP coverage. The "population need for PrEP" (PPN) is estimated based on the number of people needed to treat (NNT) with PrEP to prevent an additional HIV infection in subpopulations whose annual HIV incidence is ≥ 1 %. This is done in three steps: 1) calculating NNT for each transmission group using 1 % incidence threshold and clinical trial-and cohort-generated evidence of the degree of PrEP effectiveness in each transmission group, 2) estimating the proportion of new HIV infections in subpopulations with incidence at least 1 % from epidemiologic data, 3) multiplying estimates from steps 1 and 2 with the number of new HIV infections for each transmission group from Surveillance. The estimates for each transmission group are then added together, and the number of current PrEP users is finally added to this estimate to produce PPN. This method is relatively easy to calculate and can provide public health authorities at the national, state, or local level with pragmatic estimates of PrEP "need" among different demographic or transmission groups, which can help with planning, resource allocation, and monitoring progress.