Cholera was a devastating disease which killed thousands in London during the middle of the 1800’s. Nobody at that time was sure of how this disease was transmitted. Many felt that it was an air borne disease and that it was coming from gaseous emissions caused by decaying matter. Others thought that it was caused microbes too small to be seen. The actual cause was eventually discovered through the analytical scientific studies of John Snow.
John Snow came from humble labouring origins in York and was the oldest of nine children. He took three apprenticeships with medical practitioners before obtaining an MA at the University of London in 1844. He was famous initially for the administration of chloroform to Queen Victoria during the births of her children. Later when the cholera epidemic struck in 1853-54 he used his considerable intellectual skills to find the cause of the outbreak. He was convinced that the disease was caused by microbes rather than gaseous emissions. His views were initially resisted but over time the measures he proposed were accepted. John noted that between two cholera outbreaks there was a change of water supply which was free from the sewage of London. He noted that two water companies were supplying pumps within the same area. Through analysis of cholera deaths based on which water supply was used he was able to show that cholera was significantly higher in those drinking water that had been contaminated by sewage. An outbreak of cholera in August 1854 was associated with a particular pump in Broad Street. Again through analysis of deaths in the area John was able to show that the contaminated pump was the prime source of the outbreak.
Cholera deaths near the Broad Street pump
By using maps of the Broad Street area John was able to show in a geographical form how the deaths were directly related to the pump in that area. Each death taken from tabular data was shown on the map. This was an early example of the capabilities of GIS in that the evidence of how this outbreak occurred could be more easily understood by the locating each death on a map.
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