Epidemiological data demonstrate a clear relationship between antibiotic exposure and the development of Clostridium difficile infection (CDI). The precise relationship between the type, timing, and history of antibiotic exposure, and the development of CDI is complicated, and not precisely understood. Basic relationships between antibiotic exposure and CDI are known and inform antibiotic delivery practices in connection with healthcare outcomes. However, local, ecologic-level patterns of antibiotic use vary widely nationwide, which likely reflects a corresponding heterogeneity in CDI risk across different facilities and patient populations. In an ongoing effort to inform improved health outcomes in the United States, the CDC is interested in predicting the expected reduction in rates of CDI upon a reduction in high-risk antibiotic use. Because of some recent, related modeling work we had done, we were contacted to assist in this analysis with the CDC. In this talk, I will briefly review the epidemiology of Clostridium difficile, discuss the principal question that the CDC is interested in addressing, and discuss our involvement and contribution to their analysis.