So I ran across an infographic the other day that was basically a breakdown of how Ebola spreads (created by the MPH program at USC). My first reaction to the infographic was “Ewww. That’s nasty!” My second was to wonder how they had figured all of this out. Well, the answer is “Epidemiology”. It’s gross. It’s weird. It’ll make you afraid to touch anything. And because I firmly believe in shared misery, I am going to share about the interesting and fascinating history of epidemiology.
Epidemiology is a surprisingly old discipline. Hippocrates of Kos, considered by many to be the father of western medicine, was probably the first person to sit down and get serious about it. In his day (460 B.C.E.-370 B.C.E.) people generally had this idea that if you got sick it was basically because the gods thought it was funny.
Hippocrates apparently did not have the kind of sense of humor that tended to get him invited to Olympus to chill with the gods. This being the case he sat down and gathered around a few of his Greek buddies for a chat. It basically went something like this.
Hippocrates: Hey guys. So listen. About this whole illness thing, I’m confused.
Buddies: What confuses you about it, Hippocrates?
Hippocrates: You tell me that illness is caused by the gods?
Buddies: Well, yes Hippocrates. They have a terrible sense of humor and worse temper. Zeus is a mean drunk.
Hippocrates: But how can we be certain that this is true? I have been ill several times but have never encountered a god.
Buddies: Well, we know it is true because we haven’t found a better explanation.
Hippocrates: If only there were a method we could use to study how disease is spread and progresses. Woe is me!
Buddies: Why don’t you try that new invention that Aristotle guy from next door created?
Hippocrates: You mean Logic?
Buddies: Yes, Hippocrates. It is a wonderful method by which we apply reason to the facts in order to find the connections between them.
Hippocrates: Well, we’ve already stolen Socrates’ method of dialogue, we might as well steal Aristotle’s logic too.
With this, Hippocrates sat down and began to study diseases using logic as his guide. The result was him coming to the belief that illness was the result of environmental conditions and human behaviors. He coined two terms used today in epidemiology to this day to describe two different types of mass disease, endemic (diseases specific to some locations and not others) and epidemic (diseases that seem to appear and disappear over time). The gods had little to do with it.
Of course, he didn’t get it all right. He also concluded that the environmental factors and human behaviors that brought on diseases did this by unbalancing the levels of body fluids a person has. You can thank this belief for the concept of bleeding a patient. Still, he got us started with the idea of being able to trace the origin and path of disease.
It’d be almost two more millennia before the next big move came along. In the 1500s people had come up with this idea that disease was caused by bad air. At that point in time two things had been going on. Europe was finally starting to recover from a series of plagues, and city dwellers had the habit of leaving their trash in the streets. This led people to conclude that the nasty smelling air caused by rotten trash in the streets were what spread disease.
Fortunately for epidemiology (and for us) a particular bright young Veronan named Girolamo Fracastoro figured this really wasn’t what was up.
“Look,” he said, “I am quite aware of the fact that trashing our streets makes things stink. Trust me, I live here. We need to clean this mess up. But believe me, breathing air doesn’t kill you. Kind of the opposite, in fact.”
Girolamo proceeded to develop the idea that diseases actually were the result of really small things in the air, not the air itself. Based on this he developed the idea that if people, you know, washed their hands, bathed, and did other hygiene related things they won’t get sick as often. Most of Europe (and its colonies) thumbed their noses at him and laughed, but hygiene became fairly popular in the Italian principalities. Funny thing… it worked. Girolamo’s ideas about little bitty things causing diseases and how you catch them actually proved to be correct.
At this point it simply came down to refining the idea and figuring out the specifics for individual diseases. Several people began working on this over the ensuing years, but it was up to a Brit named John Snow. In 1854, an outbreak of Cholera was laying waste to a portion of Soho in London. In three days 127 people died from the disease. After only twelve days the death toll was around 500.
Snow, like most Northern and Western Europeans, was not familiar with Girolamo. He was, however, convinced that cholera was not caused by bad air. More importantly, he was arrogant enough to believe he could find out what did cause it. As the body count rose he packed his bags, headed to Soho, and started asking everyone in the neighborhood a lot of very nosy questions.
He took what he learned of the habits of the locals as well as the locations where victims lived or work might be and jotted them down on a map of Soho. Through this he discovered three things.
The one part of the neighborhood to not have anyone get sick were a group of monks.
The monks drank beer. And only beer.
Everyone else in the neighborhood drank water from the same well.
With a little more snooping around he discovered the well was right next to an old cesspit, and that the diapers of a baby suffering from a separate outbreak of cholera had been dumped in the pit. I’ll not elaborate, but you can guess what was happening. Armed with these facts he proceeded to convince the authorities to disable the well. Low and behold, the outbreak stopped.
Snow had just conclusively demonstrated that disease had a vector, that the vector could be traced, and that knowing the vector could end an epidemic. While a number of people still had doubts, including later convert Florence Nightingale, Girolamo and Snow had basically managed to create the foundation of epidemiology, the idea that itty bitty things caused disease, that you could find out what circumstances allowed them to do it, and that you could trace them back to the source and stop them.
These days we have far more advanced equipment. Our understanding of germ theory and of contagion has expanded well beyond anything that Hippocrates knew. We’ve managed to formalize the process, test the findings scientifically, and codify how it all works.