Prospective health care: the second transformation of medicine

At the beginning of the 20th century, the emerging sciences of physiology, pathology, chemistry, biochemistry, microbiology and radiology had the potential to change medicine from a practice based on mythology and anecdotal observations to one grounded in experimental science. Particularly powerful was the development of the germ theory, which identified microorganisms as the cause of many diseases prevalent at that time. The medical profession did not, however, easily incorporate science into practice until several decades later, when the development of academic medical centers enabled a science-based approach and the first major transformation of medical practice.The impact of science on medicine has been striking. The strengths of the reductionist method, which simplifies the concept of pathogenesis to the smallest number of causal factors, are shown by the burgeoning understanding, at a molecular level, of human biology and the underlying causes of many diseases. Spectacular medical therapies abound, and new technology has continued to enhance the capabilities of medicine. Nonetheless, the weaknesses of the reductionist scientific approach are also reflected in our health-care system in which complex chronic diseases account for most of the health-care expenditures. We have created a model that focuses on acute treatment instead of on the prevention of chronic disease (Figure 1).The reductionist focus on specific and single etiological causes of disease is a useful strategy to understanding pathogenesis, but is limited in truly explaining disease. Even for a microbial disease for which an etiological agent is known, the outcome of infection is highly dependent on the state of the host's immune system and their general health status. In genetic diseases resulting from well understood molecular mechanisms, such as sickle-cell disease, there is a highly variable course: some individuals have severe unremitting crises leading to death by their early twenties, wherea