John Snow and the cholera problem

A Post by: Ellaheh Gohari

November 9, 2022

For my inaugural blog post, I felt it best to honor the man who gave my blog its name: John Snow. No, not Jon Snow, the House Stark protagonist who knows nothing, but John Snow, the father of modern day epidemiology whose presence can still be felt in every public health study more than a century after his death.

Snow–the epidemiologist, that is–grew up in a rapidly industrializing England where new technology gave way to thousands of jobs in factories, mass production of goods, and faster travel with railways. However, wherever industrialization made its mark, overpopulation and pollution soon followed. As thousands flocked to cities in search of jobs and countless more were born as a result of England’s newfound prosperity, English infrastructure simply could not keep up.

Unfortunately for the English, as their infrastructure floundered to catch up to their swelling population, something already had: disease. These overpopulated, polluted cities provided the perfect petri dish for an epidemic: close proximity to animals made animal-to-human disease jumps more likely, and high population density meant diseases could spread from person to person very quickly.

Thus, when cholera broke out yet again in England–specifically Soho’s Broad Street–in 1854, it wasn’t exactly a surprise. After all, cholera outbreaks were commonplace, with the prevailing theory for its spread being a “miasma.” Indeed, both doctors and the general public believed that bad air was the cause of all their cholera troubles, with an invisible toxin spreading the deadly disease from person to person.

John Snow, a leading figure in anesthesiology at the time, was not having it. Asked to research the matter by city officials, Snow decided that he would embark on field investigations, surveying affected and non-affected residents to figure out if there was a link between them. Afterward, he created what we now know as a spot map to visualize the locations where cholera-afflicted individuals lived. He noticed a trend: those who had the disease tended to get water from the Broad Street pump. Finally, he had found a potential cause for the spread of cholera; not the air, but the sewage, which had traces of cholera patients’ waste and got filtered into the water pump for drinking.

Though it took a while to convince the city of his theory, they eventually conceded to removing the pump. Cholera cases dropped, suggesting Snow was right.

The actions Snow took to come to this conclusion–developing a hypothesis, conducting field investigations, drawing a spot map, taking action, and continuing to monitor the situation–are still used in some form today. Truly the father of epidemiology, Snow’s actions during the 1854 Broad Street outbreak set a precedent for epidemiological studies of the future, and I greatly admire his work. Though he died more than a century ago, Snow’s impact on epidemiology cannot be overstated; maybe he did know something, after all.