John Snow, Cholera, and the Broadgate Pump

IN THE 1800s THE INDUSTRIAL REVOLUTION urbanised Great Britain. The populations of towns and cities swelled beyond all expectations. Overseas a growing empire brought back home fabulous wealth to a few but also unknown and new diseases to many. The capital city, London, in the 1850s was a dark, overcrowded, disease-ridden city crammed with slums and rookeries.

Cholera was a deadly and terrifying disease that caused: sudden violent vomiting and diarrhoea; extreme dehydration; death in a matter of hours. During the 1800s, several cholera epidemics struck London and other major cities. The prevailing theory at the time was "miasma theory" - the belief that diseases like cholera were spread by bad air or foul smells. This theory was wrong - but it was widely accepted by doctors, officials, and even by Edwin Chadwick. Then along came John Snow.

John Snow was born in 1813 in York. The son of a labourer made good Snow had received an education and trained as an apothecary. He eventually made it down to London to work with eminent physician John Hunter eventually becoming a well-respected physician in his own right. Snow initially worked on anaesthesia and chloroform and became so respected and renowned that he worked on two of Queen Victoria's births. However it Snow was about to become even more famous for his work on epidemics as an epidemiologist.

Snow didn't believe in miasma theory. He hypothesised that cholera was spread through contaminated water - a radical idea at the time. He began to collect data during outbreaks and noticed patterns. People who drank from certain water pumps or companies were more likely to get sick. Those who got water from clean sources often remained healthy - even if they lived in the same areas.

Snow's most famous case where he made history came in 1854 in Broad Street, Soho, London. In August 1854, a severe cholera outbreak struck Soho, killing over 600 people in a few days. Snow began to investigate by mapping the cases of cholera deaths in the area. He noticed a cluster of deaths near a public water pump on Broad Street (now Broadwick Street). People who didn't use that pump (like workers who brought their own water or nearby brewery workers who drank beer) didn't get sick. Snow presented this data to the local authorities.

The result was the handle of the Broad Streat pump was removed, disabling it. The number of new cholera cases dropped immediately. This was one of the first examples of using data and mapping to stop the spread of disease - a foundational moment in epidemiology.

The scientific importance was although Snow's theory wasn't fully accepted at the time (germ theory was still developing), his work challenged dominant ideas and laid the groundwork for future breakthroughs. Key contributions were the use of data, observation and statistics to identify a source of infection. Snow pioneered modern public health and epidemiology, and helped shift medicine away from myth and assumption towards evidence-based investigation.

Snow's legacy today is celebrated through him being a founding figure of epidemiology and as one of the first to use mapping and data analysis to track disease. He was a critical player in proving that water sanitation is essential for public health. There is even a pub named after him on Broadwick Street in London, near the site of the original pump where a replica stands there today.

Written by James Florey. James is an Official London Walking Guide @CapitalWalksLondon