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John Snow's Heroic Epiphany: a story of History, Epidemiology, and Cholera outbreaks

Updated: Jun 13, 2022

Contributing author: Jon Mitchell

Setting the Scene For the Birth of Epidemiology

Do you think this pandemic has seen a $#!% -hole let me tell you a little bit about 19th century London. It’s the height of the industrial revolution with smokestacks billowing and there's a thick haze in the air. The sewage infrastructure was incapable of coping with the growing population causing human waste to build up outside of the city and bake in the heat of the summer sun. London is about to have a nasty Cholera outbreak.

This resulted in the great stink, but what is this? Imagine human excrement overflowing into the Thames river, the one where many Londoners got their water from and washed their clothes in...yum. While you and I may not find this ideal, one microbe did; these conditions were just splendid for the bacteria Vibrio cholerae, which caused four cholera outbreaks, a severe diarrheal disease, in the 1800s. But this will set the scene for some very important events. John Snow will come on the scene and, through his work to track to find the culprit of the outbreaks, lay the foundation of Epidemiology. His work will also lead credence to the development of Germ Theory by Louis Pasture at that time.

Causes of Cholera Outbreaks: Vibrio cholerae

So, who is V. cholerae? It is a comma shaped bacterium that normally resides in salty or brackish waters and hangs out with shellfish, but it can also infect people and spread quickly through a population. It establishes in the gut and, as I said earlier, this bug causes diarrhea, but not your average diarrhea from a regular stomach bug; it is so explosive that people can lose 18 liters a day, that’s almost 5 gallons! Can you imagine, 5 milk jugs of liquid shooting out of your butt! It is far from pleasant and often deadly. The loss of that much liquid easily causes death from dehydration or electrolyte imbalances, you are literally shitting yourself to death.

Cholera is still a major issue today, with nearly 4 million cases a year resulting in thousands of deaths. Cholera outbreaks are currently seen in Yemen and Somalia. Any area with poor sanitation and lack of safe drinking water is at risk for future outbreaks of the disease. Once you get cholera, you just kind of wait for the disease to run its course and V. cholerae to vacate your system. However, treatment of oral rehydration therapy drastically reduces your chances of dying from the disease and has been the best treatment for cholera for nearly 100 years.

Artwork of Cholera victims during a cholera outbreak

John Snow: Following the Cholera Outbreak

Lego John Snow riding plush Vibrio cholerae through Londong

But back to the story. The world thought the cause of this disease was due to the miasma or that the air was bad, a theory that was based on the idea that diseases were caused by humors in the body hypothesized by Hippocrates . and the Greek Physician Galen. There was a man who would prove this idea wrong, a man by the name of John Snow (and no, not the bastard child of Ned Stark).

John Snow was quite familiar with the disease cholera by the time of the great stink, as he had been working with people afflicted with it for over 20 years. At the time, the causal agent of the disease was not known but, as a surgeon’s apprentice, John Snow came across several patients afflicted by the earlier outbreaks. He went on to go to the Hunterian School of Medicine, and later graduated from the University of London with a medical degree.

The Broad Street Pump: History, Epidemiology, Landmarl

Picture of Broad Street water pump today: forever apart of the History of epidemiology. An important landmark of the London cholera outbreak

The third cholera outbreak occurred in August of 1845, particularly in an area of London that lacked a sewer system. Having quite enough of this outbreak, John Snow interviewed many people that lived in the area, mapped out cholera deaths and found that most of the cases centered around the Broad City Pump, which was supplying water from the river. He also found that those that were not getting sick were using water from local wells.

John Snow had a theory that the disease was coming from the water supplied by the pump and not from bad air, and somehow he was able to convince local officials to take the handle off the pump and cases dropped! As a sidebar, you can visit this pump in London today, I did! And if you need more motivation to go, it is located right in front of a pub!

Despite the cases of deaths dropping off, people were not convinced that water was the source of the disease. However, John would be able to show more proof of his theory soon, as another outbreak occurred in the following months. The area of London hit was serviced by 2 water companies. Both companies took water from the Thames river, Lambeth Company had water coming from the river more upstream, an area where the water was cleaner, while the Southwark and Vauxhall Company had water coming from an area that was heavily contaminated with sewage.

John Snow‘s investigation identified that people drinking and using water from the Southwark and Vauxhall company had fatality rates from cholera 14 times higher than people using the other companies' water during the first 4 weeks of the cholera outbreak. This may not have proven that the disease was coming from bacteria, but it clearly demonstrated that miasma was not the cause.

Although John Snow never knew, the causative agent of the disease was discovered that same year by an Italian physician, Filipo Puccini, it would go unnoticed until 1883 when Robert Koch was also able to isolate it. Don’t worry though, in 1960, Pucini was declared as the one to identify V. cholerae as the bacteria and so the name he gave the microbe is still used today.

The Birth Of Epidemiology

Through his work of investigation and statistics, John Snow developed the basis of Epidemiology, a branch of medicine that is used to determine the origins and patterns of disease and health. It is how we find the source of E. coli outbreaks coming from spinach, or how we try to determine which flu vaccines to develop each year.

Although the field utilizes more advanced techniques nowadays, some that were used by John Snow are still in practice! Fundamentally, John Snow was a contact tracer. During the COVID-19 outbreak, the disease was able to spread globally due to a lack of contact tracing. Since then, contact tracing has employed hundreds of people who are responsible for the safety and reducing the spread of the disease. Contact tracers, like John Snow, interview people who have the disease of interest to help determine who else might have been exposed and thus help curb the spread of the disease. So, if you know any contact tracers, thank them today! They are doing great work to help keep us safe. And if you are ever contacted by a contact tracer make sure to answer their questions as completely as you can. You could save someone's life, it’s that important!

Plaque at the broad city pump commemorating John Snow as the father of epidemiology

If you would like to read more about microbes in human history, check out our blog on Syphilis or our four-part piece on monstrous microbes.

Do you know any interesting facts about cholera, or is there a microbe that you think we should cover? Let us know by emailing us or leaving a comment below!

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