John Snow

Monday, December 11, 2006

Theodore Dalrymple has posted an interesting book review over at City Journal on The Ghost Map: The Story of London’s Most Terrifying Epidemic—and How It Changed Science, Cities, and the Modern World, by Steven Johnson, which describes the triumph of epidemiology over cholera in nineteenth-century London.

New epidemic diseases, even if they kill fewer people overall than the old ones, are particularly frightening, making it almost impossible for people to proportion their anxiety according to the objective risks. Though cholera was not one of the greatest killers of the nineteenth century (tuberculosis easily took the palm in Western Europe), it was new and unfamiliar when it first reached Britain in 1831. The suddenness of the epidemics it caused provoked panic; but by the time Robert Koch proved the bacteriological cause in 1883, cholera had not shown up in Britain for nearly 20 years.

Not bacteriology but epidemiology and sanitary engineering defeated cholera. The 1854 cholera epidemic in London, and the subsequent removal of the handle of the Broad Street pump by John Snow, was to epidemiological history what the Declaration of Independence was to American history.


[Snow] was responsible for the greatest single feat of epidemiology ever. It would hardly be too much to say that he founded the discipline.


By examining the distribution of cases, starting from the new hypothesis that cholera was waterborne rather than miasmatic, Snow deduced that the epidemic's source was contaminated water from the Broad Street pump, and he persuaded the reluctant authorities to remove the pump handle so that water could no longer flow. A local clergyman, the Reverend Henry Whitehead, at one time skeptical of Snow's theory, then proved that the initial patient who began the epidemic (the index case, as epidemiologists call it) had poisoned the pump's water supply.

It took a while before everyone accepted the waterborne nature of cholera, though the theory did win over the leading medical statistician of the day, William Farr, who initially believed that it was elevation above sea level that accounted for the distribution of cases, with filthy, cholera-carrying air stifling lower elevations. One of the greatest engineering projects of all time, the construction of a proper sewage system and clean water supply for London, then got underway, and no large-scale waterborne epidemics have plagued the city since. Indirectly, Snow made vast urban agglomerations safe, for the developed world soon copied London's example. [bold added]
This story amazes me for two reasons. First of all, Snow did a remarkable bit of original thinking that very quickly started saving lives. Second, thanks to his own efforts, basically everyone takes healthy urban living so much for granted that few remember the man. Chalk one up to the discipline of history for reminding us of just what a remarkable achievement that aspect of our daily lives really is.

-- CAV

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