Thursday, November 12, 2009

The Birth of Epidemiology

Last week, I wrote about public health in Ancient Greece and Rome as part of my series on the history of public health. Today I’m bringing you the third installment in that series, about the 1854 cholera epidemic in London and the founding of the field of epidemiology.

Imagine that one day, while going about your life, you begin to “feel an odd sense of unease, accompanied by a slightly upset stomach. The initial symptoms themselves would be entirely indistinguishable from a mild case of food poisoning. But layered over those physical symptoms would be a deeper sense of foreboding. Imagine if every time you experienced a slight upset stomach you knew that there was an entirely reasonable chance you’d be dead in forty-eight hours. Remember, too, that the diet and sanitary conditions of the day... created a breeding ground for digestive ailments, even when they didn’t lead to cholera. Imagine living with that sword of Damocles hovering above your head—every stomach pain or watery stool a potential harbinger of imminent doom.”

–Steven Johnson, The Ghost Map, p. 32

In the summer of 1854, London was struck by a cholera epidemic. The disease took the city of more than 2 million by storm, sickening people overnight, causing large numbers to die, and compelling many more to evacuate their neighborhoods for fear of getting sick. No one seemed to know what would stop the disease: although many theories for the cause and spread of the disease had been proposed, they didn’t hold water, and most of the suggested remedies were ineffective.

One person who was particularly critical of the theories that had been proposed was a physician named John Snow, who practiced in the neighborhoods of London. Snow had for many years been interested in diseases, and was well known for his work in the field of anesthesiology. Although he was not confident about what was causing so many people to become ill, he had his own theories, and began making a careful record of cases of the disease as soon as it struck.

While visiting his patients, Snow made careful notes about who contracted the disease, and where these people lived. By marking the cases on a map, he soon discovered a pattern: he realized that the incidence of disease seemed to be related to where people got their water. He discovered that one pump in particular: the Broad Street pump, seemed to be causing a lot of people to become ill. In a letter to the Medical Times and Gazette, Snow wrote:

On proceeding to the spot, I found that nearly all the deaths had taken place within a short distance of the [Broad Street] pump. There were only ten deaths in houses situated decidedly nearer to another street-pump. In five of these cases the families of the deceased persons informed me that they always sent to the pump in Broad Street, as they preferred the water to that of the pumps which were nearer. In three other cases, the deceased were children who went to school near the pump in Broad Street...

Eventually, he came to believe that to stop the outbreak it was necessary to stop people from using water from the Broad Street pump. City officials were convinced to remove the handle of the pump, and this proved effective in stemming the spread of the disease. In the end, it was discovered that fecal bacteria had begun to leak into the well, and it became clear that the polluted water - caused by the abundance of fecal matter which spreads cholera - was the cause of the disease.

Snow's discovery of the role of polluted water in spreading disease demonstrates again the importance of sanitary measures, and the work of those who are instrumental in making our cities clean. Furthermore, Snow's work laid the foundation for our modern day understanding of how diseases spread, which continues to be important to ensuring the health of our communities.

For a fascinating, thorough account of this story I highly recommend reading The Ghost Map, by Steven Johnson. The book, which provided the information for this post, chronicles the outbreak and the efforts to solve the mystery and is an enjoyable read.

This is the part two in series on the history of public health which I am writing in anticipation of Public Health Thank You Day, a time when Research!America and other leading health organizations recognize public health heroes whose work helps keep our drinking water safe, air clean and children healthy. My hope is that these posts will help illustrate how far we've come, and how much more remains to be done.

To read the first post, which gives an overview of the history of public health history, click here.
To read the second post, about public health in Ancient Greece and Rome, click here.

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