Statistical methods have been widely used in studies of public health. Although useful in clinical research and public health policy making, these methods could not find correlation among health conditions automatically, or capture the temporal evolution of causes of death correctly. To cope with two challenges above, we implement an unsupervised machine learning model, termed topic models, to investigate the mortality data of the United States. Our model successfully groups morbidities based on their correlation, and reveals the temporal evolution of these groups from 1999 to 2014, which are also validated by existing literature. This work could provide a novel view for clinical practitioners to provide more accurate healthcare service, and for public health policymakers to make better policy.