Changes

Simply talking to people, finding out when and where incidents of infection occurred, and then mapping that data helped to create among the first maps of a disease outbreak. This work made him one of the key founders of epidemiology and public health. Soon after these outbreaks, London's sanitation improved, with the pump replaced, and with the work formed the basis of public health strategies that helped to diminish future outbreaks.<ref>For more on John Snow's work, see: Hempel, Sandra. <i>The Medical Detective: John Snow, Cholera and the Mystery of the Broad Street Pump</i>. London: Granta Books, 2007.</ref>

Snow's work suggested that it was possible to track down the source of illness (not just Cholera) and track its spread. Early forms of contact tracing were applied to other infectious diseases as the late 19th century progressed. Tuberculosis (TB) was one of the biggest concerns during the rapid urbanization in the late 19th century. Cramped conditions and infected droplets made the spread of this disease rapid in the growing cities of Europe and North America.