We develop a theoretical model that incorporates the two channels through which screening may reduce prevalence. The model is based on a hospital composed of N treatment units (e.g., ICU and ER) divided into n DUs, that transfer patients between one another and an outside population. Disease prevalence in each DU is determined by an SIS model based on the multi-institutional framework of Smith, et al. (1, 2) . A DU's prevalence is a function of its own screening level (s) and that of their neighbors (š).