Koch's postulates are four criteria designed to establish a
causative relationship between a
microbe and a
disease. The postulates were formulated by
Robert Koch and
Friedrich Loeffler in 1884, based on earlier concepts described by
Jakob Henle, and refined and published by Koch in 1890. Koch applied the postulates to describe the
etiology of
cholera and
tuberculosis, but they have been controversially generalized to other diseases. These postulates were generated prior to understanding of modern concepts in microbial pathogenesis that cannot be examined using Koch's postulates, including
viruses (which are obligate cellular parasites) or
asymptomatic carriers. They have largely been supplanted by other criteria such as the
Bradford Hill criteria for infectious disease causality in modern public health.