John Snow and the 1854 Broad Street Cholera Outbreak

Many historians trace modern public health and epidemiology to the day in 1850s when Dr. John Snow, having discerned the link between cholera outbreaks in London and water sources used by the afflicted populace, removed the handle of the Broad Street water pump. Thus one cholera epidemic was stopped, but it would still be years before the etiology of cholera was discovered.

In the mid-19th century, the Soho district of London had a serious problem with filth due to the large influx of people and a lack of proper sanitary services. Many cellars (basements) had cesspools of nightsoil underneath their floorboards. Since the cesspools were overrunning, the London government decided to dump the waste into the River Thames. This action contaminated the water supply, leading to the cholera outbreak.


Outbreak
On 31 August 1854, after several other outbreaks had already occurred elsewhere in the city, a major outbreak of cholera struck Soho. Dr Snow later called it "the most terrible outbreak of cholera which ever occurred in the kingdom."

Over the next three days 127 people on or near Broad Street died. In the next week, three quarters of the residents had fled the area. By 10 September, 500 people had died and the mortality rate was 12.8 percent in some parts of the city. By the end of the outbreak 616 people died.

Snow was a skeptic of the then-dominant miasma theory that stated that diseases such as cholera or the Black Death were caused by pollution or a noxious form of "bad air". The germ theory was not widely accepted by this time, so Snow was unaware of the mechanism by which the disease was transmitted, but evidence led him to believe that it was not due to breathing foul air. He first publicized his theory in an essay On the Mode of Communication of Cholera in 1849. In 1855 a second edition was published, with a much more elaborate investigation of the effect of the water-supply in the Soho, London epidemic of 1854.

By talking to local residents (with the help of Reverend Henry Whitehead), he identified the source of the outbreak as the public water pump on Broad Street (now Broadwick Street). Although Snow's chemical and microscope examination of a sample of the Broad Street pump water was not able to conclusively prove its danger, his studies of the pattern of the disease were convincing enough to persuade the local council to disable the well pump by removing its handle. Although this action has been popularly reported as ending the outbreak, the epidemic may have already been in rapid decline, as explained by Snow himself:

Snow later used a spot map to illustrate how cases of cholera were centred around the pump. He also made a solid use of statistics to illustrate the connection between the quality of the source of water and cholera cases. He showed that the Southwark and Vauxhall Waterworks Company was taking water from sewage-polluted sections of the Thames and delivering the water to homes with an increased incidence of cholera. Snow's study was a major event in the history of public health, and can be regarded as the founding event of the science of epidemiology.