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10 NOVEMBER 2019

John Snow: The “King” of Epidemiology

The first words that come into most people’s mind when they hear the name “John Snow” is Game of Thrones and iron throne or Westeros. However, John Snow was far more than a fictional character. Actually, John Snow was one of the most famous British physicians, who revolutionised medicine and is considered to be one of the founders of epidemiology.


John Snow was born in York on 15 March 1813. At the age of 14, he was apprenticed to a surgeon and after 9 years he moved to London in order to officially start his medical education. In 1844, he graduated from the University of London, while in 1850, Snow was admitted to the Royal College of Physicians. At that time, London and many other urban centres around Europe were infested by cholera.


Cholera is an acute diarrhoeal infection caused by the bacterium Vibrio cholerae. Its symptoms involve diarrhoea, nausea, vomiting and dehydration. Overall, those symptoms cause imbalance in the electrolytes of the blood resulting in muscle cramps and shock. The primary source of cholera infection is contaminated water and food supplies. Interestingly, many people may not show any symptoms at all when they ingest the bacterium vibrio cholerae. However, the bacteria can still get transmitted through the stool, faeces of those people and contaminate the water table. Nowadays, it is estimated that 1.3 million to 4.0 million cases of cholera occur annually, which lead from 21,000 to 143,000 deaths worldwide. Overall, cholera has killed dozens of millions of people around the world. The majority of cholera cases can be treated via hydration or rehydration.


During the 1900s, societies in Europe would have common water supplies, pumps around the cities, where people could access potable water. Nevertheless, little was known at that time for the existence of microorganisms, which were "invisible" and harmful (the so called "germ theory"). During the cholera epidemic, Snow hypothesised that the bacterium Vibrio cholerae could spread through the water supply used by citizens of London on a daily basis. So, he started mapping all the different cholera cases occurring throughout Soho, London. Eventually, he was able to identify a pump, which was located in Broad (now Broadwick) Street in Soho that was correctly regarded as a cholera source. Then, he changed the handle of the pump with a new one and the cases of cholera decreased significantly.

The original plot created by Snow to map all the known cholera cases in Soho.


Furthermore, John Snow was among the advocates of the “germ theory”, namely the idea that microorganisms, called pathogens, are the underlying cause of disease. Nonetheless, this theory was criticised and not widely accepted until the 1860s, when Snow actually died (16 June 1858).


John Snow performed the first ever recorded epidemiological study, where he analysed the pattern and cause of a specific disease in a specific sample population. Unfortunately, Snow is yet another folk hero, whose great deed is still not popular among our society. His contribution to medical science, however, was unavoidably exploited in the future and he is justifiably named the father or "king" of epidemiology.

John Snow memorial pump found in Broadwick Street, Soho, London.