Epidemiology is the study of the distribution, occurrence and spread of disease. It is thus closely related to geography, which examines humans and their relation to the environment.
The first comprehensive epidemiological study was undertaken by Dr John Snow, who analysed fatalities in the London cholera outbreak of 1854. By linking these to one water pump in Broad Street in Soho, London, he established that cholera was a water-borne disease. That summer had been hot and the people were drinking cold water rather than boiling it for tea, as was usual.
In this area of London there were 13 pumps supplying water from wells. The cholera outbreak happened very rapidly. The majority of those who died became violently ill on the night of 31 August and died one or two days later. People began to flee if they were able; 75 percent of the population left in just a few days.
At once, Snow investigated and mapped the locations of the homes of those who had died in this outbreak. The pump central to his map was in Broad Street. Of the 89 people who died, only 10 lived closer to another pump. What was curious was that the 535 inmates of the workhouse in Poland Street were unaffected, even though it was surrounded by fatalities.
The 70 Broad Street Brewery workers also escaped the disease. But one woman in Hampstead and her niece in Islington, both over eight kilometres away from the pump, also died.