John SnowJohn Snow (15 March 1813 – 16 June 1858) was a British physician and a leader in the adoption of anaesthesia and medical hygiene. He is considered to be one of the fathers of epidemiology, because of his work in tracing the source of a cholera outbreak in Soho, England, in 1854 using spatial analysis.

John Snow was born into a labourer's family on 15 March 1813 in York and at 14 was apprenticed to a surgeon living in Newcastle-on-Tyne. In 1836, he moved to London to start his formal medical education. He became a member of the Royal College of Surgeons in 1838, graduated from the University of London in 1844 and was admitted to the Royal College of Physicians in 1850.

In 1849 Snow published a small pamphlet "On the Mode of Communication of Cholera" where he proposed that the "Cholera Poison" was spread through the contamination of food or water. This theory was opposed to the more commonly accepted idea that Cholera, like all diseases, was transmitted through inhalation of contaminated vapours.


John Snow map of SohoIn August 1854, a cholera outbreak occurred in Soho, London. After careful investigation by Snow, including plotting distribution of deaths on a map, he determined that an unusually high number of deaths were taking place near a water pump on Broad Street. Snow's findings led him to petition the local authorities to remove the pump's handle. This was done and the number of cholera deaths was dramatically reduced.

Snow's classic study offers one of the most convincing arguments of the value of understanding and resolving a social problem through the use of spatial analysis.

The image on the right shows a section of the original map by Dr. John Snow showing the clusters of cholera cases in the London epidemic of 1854.


Using Map Intelligence


Map Intelligence and John SnowLondon's Soho in 1854 was a dirty, grimy place with cow sheds, grease-boiling dens, slaughter houses and overcrowded housing under which numerous cess pits festered. Drinking water was provided by the way of street water pumps.

In the 1854 London Cholera epidemic the worst-hit areas at first were Southwark and Lambeth. Soho suffered only a few, seemingly isolated, cases in late August. Then, on the night of the 31st, what Dr Snow later called "the most terrible outbreak of cholera which ever occurred in the kingdom" broke out. During the next three days, 127 people living in or around Broad Street died. By 10 September, the number of fatal attacks had reached 500 and the death rate of the St Anne's, Berwick Street and Golden Square subdivisions of the parish had risen to 12.8 per cent -- more than double that for the rest of London. That it did not rise even higher was thanks only to Dr John Snow.

John Snow is viewed by many as a pioneer in disease mapping. He used  bars on a map to represent deaths that occurred at the specified households. His interviews and investigations led to the removal of the handle on the Broad Street pump. 

Today, John Snow would have probably kept his data in an Excel Spreadsheet and used Map Intelligence to quickly create a mapping application that could analyze his interview data. 


The Map Intellgence "1854 Broad Street Cholera Outbreak" Application


Slideshow: Click image to view a larger version.


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