• Adeline

Who is John Snow, that hero, the father of epidemiology?

Updated: Mar 29

At the moment, we talk a lot about epidemiology (and for good reason!). In the media, doctors, infectiologists and epidemiologists have never been given so much space to speak, and that's a good thing. Unlike medicine, which studies diseases at the level of the individual (diagnosis, causes and symptoms, and treatment to the patient), epidemiology is a science that looks at diseases at the level of a population (human or animal), as well as their geographic and temporal distribution. Thus, epidemiology is concerned with all environmental factors related to diseases.


But do you know how epidemiology came into being and who "invented" it?


Epidemiology is considered to have been truly born in 1854 during the cholera epidemic in London, and its inventor is a certain John Snow. No, not the character you're thinking of. John Snow, a doctor who was practicing in London at the time, a doctor of the poor people in the Soho district.


Who is John Snow?

John Snow (1813-1858) is an English doctor, born into a poor family. He became a vegetarian at the age of 17 during his apprenticeship. His first contribution to the scientific community is not the one you are thinking of. Before inventing epidemiology, he first created an inhaler to control the amount of ether vapor given to patients. His inhaler was equipped with a variator allowing for better gas delivery. This invention will contribute to the democratization of general anesthesia. He anesthetizes Queen Victoria with chloroform for the birth of Prince Leopold and Princess Beatrice (the Queen's 8th and 9th children). Unlike other doctors who seek to patent their inventions related to anesthesia, John Snow publishes his plans in order to make them accessible to all (thank you John!).





Cholera epidemics

John Snow first encounters a cholera epidemic during his apprenticeship, from October 1831 to February 1832. He confronts this epidemic alone, and one can legitimately think that it left its mark in his mind. At the time, it was thought that cholera was spread through the air, especially the infected air in slaughterhouses, as proved by the putrid smell. Imagine, if you have the courage, the sanitary state of the slaughterhouses at the time (maybe it's not so surprising that a doctor like Snow became a vegetarian). John Snow doesn't agree with this theory because he notes that slaughterhouse employees are not necessarily the first to be affected by the epidemic. He suspects that drinking water plays a role.





The first epidemiological mapping

In London, the drinking water for families is drawn from the Thames. Either upstream or downstream from the sewers (!!!!). John Snow places all cases of cholera on a map of London. This map shows that the majority of cholera cases are located downstream of the sewers. He explains that people become infected by absorbing fecal matter from drinking water pumped down the sewers. But no one believes him.

He was not taken seriously until the 1853 epidemic. Once again, the doctor maps the places where the sick and 578 dead lived and worked. This mapping reveals that the deaths are linked to a public water pump and that cholera was being spread by the distribution of water. John Snow has identified the source of the contamination. He has the arm of the water pump removed and the epidemic eventually disappears. That's how John Snow saved hundreds of lives, maybe more and became a hero (a real one!).

The science of epidemiology was born.


Due to epidemiology, it is now possible to understand how epidemics originate and spread and to identify the epicenters.




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