The goal of this project will be to extend the population attributable fraction (PAF) work to assess the cost-effectiveness of STI screening in terms of reducing HIV incidence. Specifically, this project merges two existing CAMP-supported projects: the PAF model and the STI guidelines model. We will assess the downstream effect of implementation of the STI guidelines on HIV incidence among MSM with respect to quality-adjusted life years (QALYs) gained under different STI testing scenarios.