John Snow: The London Cholera Epidemic of 1854
By Scott Crosier
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Snow (1813-1858) was educated at a private school until, at the age of
fourteen, he was apprenticed to a surgeon living at Newcastle-on-Tyne.
After serving as a colliery surgeon and unqualified assistant during
the London Cholera epidemic of 1831-2, he became a student at the
Huntierian School of Medicine in Great Windmill Street, London. After
two years of schooling, he was accepted a member of the Royal College
of Surgeons of England. He graduated M.D. of the University of London
In 1849 Snow published a small pamphlet "On the Mode of
Communication of Cholera" where he proposed that the "Cholera Poison"
reproduced in the human body and 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 vapors. Although he was awarded for this
work, without the technology and knowledge that we have today, Snow had
no way to prove his theory.
wasn't until 1854, when Cholera struck England once again, that Snow
was able to legitimate his argument that Cholera was spread through
contaminated food or water. Snow, in investigating the epidemic, began
plotting the location of deaths related to Cholera (see illustration).
At the time, London was supplied its water by two water companies. One
of these companies pulled its water out of the Thames River upstream of
the main city while the second pulled its water from the river
downstream from the city. A higher concentration of Cholera was found
in the region of town supplied by the water company that drew its water
form the downstream location. Water from this source could have been
contaminated by the city's sewage. Furthermore, he found that in one
particular location near the intersection of Cambridge and Broad
Street, up to 500 deaths from Cholera occurred within 10 days.
After the panic-stricken officials followed Snow's advice to
remove the handle of the Broad Street Pump that supplied the water to
this neighborhood, the epidemic was contained. Through mapping the
locations of deaths related to Cholera, Snow was able to pinpoint one
of the major sources of causation of the disease and support his
argument relating to the spread of Cholera.
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. Nonetheless, there is some
controversy regarding whether Snow made the map prior to or after the
removal of the pump handle and about the timing of this removal
relative to the temporal pattern of cholera deaths.
While mapping has become a standard research approach in
medical geography and epidemiology, today's researchers express the
incidence of disease as a rate relative to the population or to the
population within age cohorts (e.g., deaths per 1,000 population) so as
to factor out the influence of population density. Using such
refinements to the methods employed by Snow, mapping and spatial
statistical techniques assist medical practitioners in understanding
the diffusion and spread of diseases within communities and across the
This is a portion of the original map created by Dr. John Snow. Through
plotting the deaths (signified by a line parallel to the building front in
which the people died), Dr. Snow was able to trace the spread of Cholera to
the pump at the corner of Cambridge and Broad Street. Click the image to view
a bigger area.
Snow on Cholera, New York: The Commonwealth Fund: Oxford University Press. 1936.
On the Mode of Communication of Cholera, 8vo, London, 1849 ; 2nd ed. 1855.
Rosenberg, Charles E. The Cholera Year. Chicago: The University of Chicago Press. 1962.
Jones, Kelvyn and Graham Moon. Health, Disease and Society: A Critical Medical Geography. Routledge. London: 1987.
Cliff, A. and P. Haggett. Atlas of Disease Distributions, Blackwell, Oxford. 1988.
Tufte, E. R. "Visual and statistical Thinking: Displays of Evidence for making Decisions." Visual Explanations: Images and Quantities, Evidence and Narrative. Cheshire, Connecticut, Graphics Press: Chapter 2. 1997
Brody, H., M. R. Pip, et al. "Map-making and myth-making in Broad street: The London Cholera epidemic, 1854." The Lancet 356, (9223): p64-68. 2000
Snow's Cholera Map
John Snow Info
John Snow - A Historical Giant in Epidemiology
About.com's Page on John Snow
Copyright © 2001-2006 by Regents of University of California, Santa Barbara,
Page Author: Scott Crosier