January 2016

Unknown Waters

Cholera is an infectious disease of the small intestine caused by a number of strains of the bacteria Vibrio cholerae, spread mostly by contaminated water or food. The disease is believed to have originated in India in the early 1800s. Six cholera pandemics followed, killing millions of people as the disease quickly spread around the world. Today, researchers estimate between 1.4 and 4.3 million cases of cholera annually, resulting in between 28,000 and 143,000 deaths each year.

The English physician John Snow (1813–1858) has become an iconic figure in Public Health for his role in identifying the source of a cholera outbreak in the Soho district of London in 1854 during the third cholera pandemic. With help from a member of the local clergy, Rev. Henry Whitehead, Snow correctly identified a public water pump on Broad Street as the source of the Soho epidemic that ultimately took the lives of more than 600 people.

Vibrio cholerae

As a teenager, John Snow served as an apprentice to a surgeon in the town of Newcastle, England. During that time, in 1831, the town was overtaken by the disease. Snow immediately took great interest in the subject. By 1850, Snow had graduated from the University of London and had been admitted to the Royal College of Physicians. He had also become one of the founding members of the Epidemiological Society of London, brought together in response to another severe cholera outbreak in 1849.

Snow was a harsh critic of miasma theory, the prevailing theory at the time that infectious diseases such as bubonic plague and cholera were spread by “bad air.” While unsure of the exact mechanism, Snow theorized instead that these diseases were spread through human contact. He published his theory in a famous 1849 essay titled On the Mode of Communication of Cholera. In early 1855, Snow published a second edition as a book citing the Soho outbreak as evidence to support his theory.

While local officials discounted Snow’s ideas, during the outbreak he was able to convince them to remove the handle on the Broad Street pump as an experiment. The number of new cholera cases dropped dramatically. While continuing his investigation, Snow then met Whitehead, a central figure in local community and provided him with a copy of his new book. Like most others, Whitehead was critical of Snow’s theory, so much so that he set about to disprove it on his own.

While previous attempts to gain detailed information on individual cases had languished, Whitehead’s standing within the community allowed him to obtain the name, age, hour of attack, and Broad Street pump connection for every person who had died in the epidemic. Upon gathering and examining this data, Whitehead conceded that Snow’s theory about the water pump was indeed correct.

Armed with this additional data from Whitehead, Snow was able to produce his now-famous dot map of the Soho outbreak. With Whitehead’s help, he eventually discovered that the well for the pump had been dug just a few feet from an old cesspit containing fecal matter from a cholera-stricken child. The finding confirmed Snow’s hypothesis and dealt a serious blow to miasma theory.

Given his role in the Soho outbreak investigation, John Snow is considered one of the fathers of modern epidemiology. A plaque, showing a water pump with its handle removed, commemorates Snow on the spot where the original pump stood.


John Snow’s work contributed to sanitary reform, both in regulations  and sanitary engineering. At the time of the Soho outbreak, London was considered among the least sanitary cities in the industrialized world. By the end of the century, however, London was regarded as among the  most progressive cities in terms of clean water and other government-coordinated services contributing to public health.


The number of cholera-related deaths in the Broad Street area of Soho, London, over a three-day period in 1854. More than 600 died.


The number of cholera pandemics  documented since 1817, the most  recent originating in  Indonesia  in 1961.