In August of 1854 Soho, a suburb of London, was hit hard by a terrible outbreak of cholera. Dr. John Snow lived near Soho, and immediately went to work to prove his theory that contaminated water was the cause of the outbreak.
“Within 250 yards of the spot where Cambridge Street joins Broad Street there were upwards of 500 fatal attacks of cholera in 10 days,” Dr. Snow wrote “As soon as I became acquainted with the situation and extent of this erruption of cholera, I suspected some contamination of the water of the much-frequented street-pump in Broad Street.”
Dr. Snow worked around the clock to track down information from hospital and public records on when the outbreak began and whether the victims drank water from the Broad Street pump. Snow suspected that those who lived or worked near the pump were the most likely to use the pump and thus, contract cholera. His pioneering medical research paid off. By using a geographical grid to chart deaths from the outbreak and investigating each case to determine access to the pump water, Snow developed what he considered positive proof the pump was the source of the epidemic.
Besides those who lived near the pump, Snow tracked hundreds of cases of cholera to nearby schools, restaurants, businesses and pubs.
Snow also investigated groups of people who did not get cholera and tracked down whether they drank pump water. That information was important because it helped Snow rule out other possible sources of the epidemic besides pump water.
On 7 September 1854, Snow took his research to the town officials and convinced them to take the handle off the pump, making it impossible to draw water. The officials were reluctant to believe him, but took the handle off as a trial only to find the outbreak of cholera almost immediately trickled to a stop. Little by little, people who had left their homes and businesses in the Broad Street area out of fear of getting cholera began to return.
With that one action, Snow stopped the cholera outbreak, showed a skeptical world that disease could be transmitted by contaminated water, and invented the field of epidemiology.
A metaphor we’ll return to tonight is moving the world with a long enough lever. He did all that with the absence of a lever.
edit