a perverse teachable moment

Cholera outbreak creeps closer to Haiti's capital

With cholera in the news, I'll take the opportunity to mention the earliest use of statistical graphics in epidemiology: Dr. John Snow's map of water wells in London during the cholera outbreak in 1854. Snow plotted on a street grid, 1) the location of cholera cases, and 2) the location of public water wells. From this simple graph he deduced that all cholera cases derived from folks who got their water from a single well.
His work is widely regarded as beginning of scientific epidemiology and public health.

Here's his map:

Until Snow's study, cholera was attributed to 'miasmas' (literally, "bad airs").
As a result of his pioneering work during the 1854 Broad Street cholera epidemic, it was finally recognized that cholera was a water-borne disease, spread by contaminated water.

In Snow's own words:

On proceeding to the spot, I found that nearly all the deaths had taken place within a short distance of the [Broad Street] pump. There were only ten deaths in houses situated decidedly nearer to another street-pump. In five of these cases the families of the deceased persons informed me that they always sent to the pump in Broad Street, as they preferred the water to that of the pumps which were nearer. In three other cases, the deceased were children who went to school near the pump in Broad Street...
With regard to the deaths occurring in the locality belonging to the pump, there were 61 instances in which I was informed that the deceased persons used to drink the pump water from Broad Street, either constantly or occasionally...

The result of the inquiry, then, is, that there has been no particular outbreak or prevalence of cholera in this part of London except among the persons who were in the habit of drinking the water of the above-mentioned pump well.

I had an interview with the Board of Guardians of St James's parish, on the evening of the 7th inst [Sept 7], and represented the above circumstances to them. In consequence of what I said, the handle of the pump was removed on the following day.
—John Snow, letter to the editor of the Medical Times and Gazette