(Intro)

These days, most people are like me.  They hear the name Jon Snow and they think of Game of Thrones or they think of that British news anchor, but before there was Jon Snow the news anchor and before there was Jon Snow the fan-beloved brother of the Night's Watch, there was John Snow with an H, a 19th century medical doctor from England, but Dr. John Snow has a few claims to fame, including developing early anesthetics and administering anesthesia for the queen while she delivered two of her kids, but mostly, he is remembered for the way he fought cholera.

In the 1850s, his timely action and clever thinking stopped an outbreak, and even though he was never recognized during his lifetime, he's now considered one of the founders of epidemiology.  Our story begins in mid-19th century London, which was, in a word, gross.  In two words, super gross!

Like many cities in the 1800s, London saw a huge increase in population and with that came a huge increase in poop, which nobody knew quite how to deal with.  Sewer systems hadn't quite spread to the entire city, so in places like the SoHo district, people sloshed their waste into the streets, dumped it into overflowing cesspools, or trucked it over to the Thames River, the river that notably also served as the city's primary water supply.

During this period, maybe unsurprisingly, London and the rest of Europe were also being plagued with persistent outbreaks of cholera, a highly infectious, sometimes deadly, diarrheal illness, and there was considerably disagreement over why.  We didn't know that bacteria and viruses were at the root of most infectious diseases, so the prevailing idea was miasma theory, which said that they were passed around by bad air.  

This is where John Snow came in.  He had encountered cholera before in mining populations and had come to believe the disease was not spread by air but by ingesting stuff contaminated with human waste.  After all, the miners brought their meals to work, didn't have a bathroom down there, and probably didn't wash their hands before eating.  Gross.

When Snow observed the situation in London, he therefore concluded that cholera was being spread by tiny fecal particles in the water, and in 1854, he got a chance to prove it.  The year before, a new cholera outbreak reached a London borough near Snow's home and it killed more than 500 people in a matter of weeks.  Based on the area, Snow was suspicious of one water pump on Broad St, specifically after his sample of the water turned up visible white flecks of organic material.  

So he obtained a list of some people who had been killed by the outbreak and began talking to their families and ultimately, he found the common factor was where those victims had gotten their water: that pump on Broad St.  Snow then took his evidence to the local officials, who agreed to take the handle off the pump to prevent people from using it, but even then, nobody really believed Snow about why, including Britain's general board of health.  It's possible that his sample size wasn't enough to convince them or maybe it was the fact that he couldn't prove what in the water was causing the illness.

In any case, Snow was confident enough in his findings that when other cholera outbreaks appeared, he continued trying to find the contaminated water behind them, and ultimately that led him to a more city-wide discovery.  At some point, Snow realized all the districts in London affected by the outbreaks had their water piped in from one of two suppliers, one that got their water from upstream of London and one that got it from downstream.

He suspected the downstream water, as you might also suspect, had a bunch of sewage in it, so cholera should have been more common in the neighborhoods that drank it.  To prove this, he began rifling through hundreds of parliamentary death records and he found that areas with downstream water had 14 times more deaths from cholera during the outbreak.  

Now to you and to me, that might seem like pretty conclusive evidence that sewage = cholera, but for various reasons, the idea still didn't catch on, and that was the end of that, or at least it was Snow's last published attempt at convincing the medical community that sewage caused cholera.  He did continue to investigate it privately and do other kinds of research, but unfortunately, he died prematurely only a few years after these events.  

The thing is, though, Snow was very right.  Cholera is typically a waterborne illness spread by sewage-contaminated water.  It just took a few more decades of work and proof that microbes can cause diseases for scientists to finally prove and accept that.  Thankfully for all of us, though, Snow's methods didn't fade into obscurity.  Even if his work was rejected in the 1850s, his outbreak management strategies are still in use today.  

His idea to map the origin of cases is a technique that is currently saving lives and it was so unique that it was a foundation of modern epidemiology.  Looking back, Dr. John Snow may not have had a sword.  He may not have had an army at his command, but he did wield mass health information and helped shape a major field of science.

So even though Snow wasn't celebrated during his lifetime, there's a lot to celebrate about him today because in the end, there's no doubting that his contributions have helped save millions of lives.

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