In 1849 Snow published what should have been another groundbreaking paper, On the Mode of Communication of Cholera, demonstrating that more people died from cholera in the area served by certain South London water companies. These drew their water straight from the River Thames, which, at this time, had around sixty sewage outlets gushing into it.
By talking to local residents (with the help of Reverend Henry Whitehead), he identified the source of the outbreak as the public water pump on Broad Street (now Broadwick Street). Although Snow’s chemical and microscope examination of a water sample from the Broad Street pump did not conclusively prove its danger, his studies of the pattern of the disease were convincing enough to persuade the local council to disable the well pump by removing its handle.
Snow later used a dot map to illustrate the cluster of cholera cases around the pump. He also used statistics to illustrate the connection between the quality of the water source and cholera cases. He showed that the Southwark and Vauxhall Waterworks Company was taking water from sewage-polluted sections of the Thames and delivering the water to homes, leading to an increased incidence of cholera. Snow’s study was a major event in the history of public health and geography. It is regarded as the founding event of the science of epidemiology.
- Gunn, S. William A.; Masellis, Michele (23 October 2007). Concepts and Practice of Humanitarian Medicine. Springer. pp. 87–. ISBN978-0-387-72264-1.
- Hapter, Thomas (1849). The History of the Cholera in Exeter in 1832. London: John Churchill