John Snow and cholera micronautes micronauts map london water fountain source vibrio cholerae cholera epidemiology

John Snow and cholera

John Snow and cholera

During the nineteenth century it was thought that infectious diseases were generated from miasmas (pollutant vapors), which were transported by air.

It was not known that germs cause diseases or that they can be transmitted through the consumption of water contaminated by faeces. During that same period, the River Thames was the water supply of London, as well as an open sewer of all the waste of the citizens. Precisely, the English capital suffered several outbreaks of cholera epidemics.

On August 31, 1854, a large outbreak of cholera killed 500 people in 10 days in the Soho area. An English doctor, John Snow (not Jon Snow), investigated how the disease was distributed in the population to try to control the outbreak. He visited the relatives of the infected and ended up realizing that there was one factor in common: those infected with cholera collected water at the Broad Street pump.

Most residents of Soho drew water at that point in the city. In addition, several victims from other neighborhoods worked in a factory that used that same water pump. Some of the children who had suffered cholera used to walk down Broad Street on their way to school. One of the most isolated cases was that of a woman who lived in a distant neighborhood but was still receiving water from Broad Street because she preferred the taste. The residents of Soho who were not related to the disease were also interviewed. None of the citizens who consumed water from their own wells had fallen ill. John Snow reported his findings to the London Board of Health on September 7 and she removed the handle of the water pump so no one could drink from it. The number of infected people decreased considerably and the outbreak ended up disappearing.

Mapa de Londres elaborat per John Snow amb els casos de cólera. Mapa de Londres elaborado por John Snow con los casos de cólera. Fuentes de agua. Fonts d'aigua. Map of London prepared by John Snow with the cases of cholera. and water pumps.

The map that John Snow made, marking the deaths of the Soho neighborhood (black bars) and the location of the water pumps. Images: General map and zoom map.

Reverend Henry Whitehead, an advocate of cholera transmitted by miasma, tried to prove that John Snow was wrong. Conversely, he discovered that less than a meter from where the water pump was located, there was a house with a cesspit. The woman of the house said that she had discarded the diapers of her son infected with cholera during a previous epidemic outbreak. Henry Whitehead ended up supporting the theory of John Snow after a leak from the cesspit to the water well was identified. Even so, the London Board of Health continued to associate the facts to the miasmatic theory, since the concept of infections transmitted by human feces was too unpleasant. At the end of the outbreak, the water pump from Broad Street was reopened.

John Snow’s work was not recognized until after his death. In 1866, William Budd acknowledged that whatever was causing the cholera was transmitted through the faeces and proposed measures to protect the water supply. In 1884, Robert Koch determined that cholera was contracted by the infection of the bacterium Vibrio cholerae. Curiously, the Italian anatomist Filippo Pacini had already isolated this bacterium the same year that John Snow published his studies, but his results went unnoticed.

Thanks to microbiology, we now know that microorganisms are responsible for infectious diseases. Epidemiology studies how diseases are distributed in a population, trying to discover the causes and how to control outbreaks.. Nowadays, John Snow is recognized as the father of modern epidemiology.

Localització de la font que va donar orígen al brot de cólera a l'actualitat. Amb una font sense mànec en honor a John Snow, així com un pub que porta el seu nom. Actual site in london where the outbreak was originated, with a fountain honouring John Snow and a pub. Sitio real donde John Snow identificó el brote de cólera con una fuente sin mango y un pub en su honor.

In the current Broadwick Street (former Broad Street) of London, a water pump without handle is found in honor to John Snow, as well as a pub with his name. Images: Map and photo.


On the causes of fevers (1839). By William Budd, edited by Dale C Smith.

A rivalry of foulness: official and unofficial investigations of the London cholera epidemic of 1854 (1998). N Paneth, P Vinten-Johansen, H Brody, and M Rip.

The changing assessments of John Snow’s and William Farr’s cholera studies (2001). John M Eyler.

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