Predicting HIV Incidence in the SEARCH Trial: A Mathematical Modeling Study

The SEARCH study provided community-based HIV and multi-disease testing and antiretroviral therapy (ART) to 32 communities in East Africa and reported no statistically significant difference in three-year HIV incidence. We used mathematical modelling to estimate the effect of control arm viral suppression and community mixing on SEARCH trial outcomes. Uganda and Kenya. Using the individual-based HIV modeling software EMOD-HIV, we configured a new model of SEARCH communities. The model was parameterized using demographic, HIV prevalence, male circumcision, and viral suppression data, and calibrated to HIV prevalence, ART coverage, and population size. Using assumptions about ART scale-up in the control arm, degree of community mixing, and effect of baseline testing, we estimated comparative HIV incidence under multiple scenarios. Prior to the trial results, we predicted that SEARCH would report a 4-40% reduction between arms, depending on control arm ART linkage rates and community mixing. With universal baseline testing followed by rapidly expanded ART eligibility and uptake, modelled effect sizes were smaller than the study was powered to detect. Using interim viral suppression data, we estimated three-year cumulative incidence would have been reduced by up to 27% in the control arm and 43% in the intervention arm compared to a counterfactual without universal baseline testing. Our model suggests that the active control arm substantially reduced expected effect size and power of the SEARCH study. However, compared to a counterfactual "true control" without increased ART linkage due to baseline testing, SEARCH reduced HIV incidence by up to 43%.