Cholera and the Power of Data Driven Insights
The year is 1854 and there is a stench hanging over London. At this point in history, the River Thames is a fetid mass of sewage, a thick scum floating on its surface. Smaller ancient rivers, long forgotten and sealed beneath the city, carry refuse directly into the river. The smell of sewage is so strong that Parliament in London is closed and moved out to the countryside. The famed engineer Joseph Bazalgette is still working on his monumental project to revolutionise the city’s ancient and inadequate sewer system.
Unknown to the population, the terrible and much feared disease, cholera, is about to strike again. The disease is a terrifying one. It causes a gastrointestinal nightmare and leaves the victim dehydrated and weak. It appears to strike without warning and can kill within hours.
The ‘miasma’ theory of disease transmission is the prevailing theory of the time. Air particles rise up and infect those who can detect the scents. The focus is on avoiding or removing of the smells. Even Bazalgette’s sewer project was founded on the theory that it will remove the smell and therefore reduce disease. But one man, John Snow, looks at the situation differently. From 1849, through the cholera outbreak in 1854 through to 1855, he carries out a series of data-driven investigations into the causes behind the outbreaks.
Patiently and painstakingly, he investigates cholera across the city, focusing especially on the growing outbreak centred in what is now the Soho district of London. Tabulating data and carefully analysing the habits and behaviours of people who do and do not become sick, he begins to build a terrifying new picture. One that implies that cholera is not transmitted through the air, but through contaminated water.
His attention centres on Broad Street. In that winding warren of streets and tenement buildings, he tracks every case. Later plotting them onto a single map, a startling insight comes to light. With pumps scattered in several locations, the cluster of deaths is largest around a single pump; the Broad Street Pump.
In his own words:
“…On proceeding to the spot, I found that nearly all the deaths had taken place within a short distance of the 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 pump which was nearer…
…The result of the inquiry then was, that there had been no particular outbreak or increase of cholera, in this part of London, except among the persons who were in the habit of drinking the water of the above-mentioned pump-well.
…I had an interview with the Board of Guardians of St. James's parish, on the evening of Thursday, 7th September, and represented the above circumstances to them. In consequence of what I said, the handle of the pump was removed on the following day…”
From: John Snow - On the Mode of Communication of Cholera, 1855
Whether the removal of the pump handle or the natural ebb of the disease contributed more to the decline, a new data-driven theory was being born.
The focus of so much of the story is on the climatic moment. The removal of the pump handle and the decline of the disease. However, there is a deeper insight in John Snow’s work. In parallel to tracking the disease and the habits of those inflicted, John Snow was also tracking who supplied the water to the various pumps and houses. He carefully linked the various pumps back to the water providers throughout the city: the Southwark and Vauxhall Company, the Lambeth Water Company, the New River Company and the Chelsea Company.
Instead of just focusing on the effects, he used the derived from a natural city-scale experiment, to try to identify the root causes of cholera. Through a painstaking analysis across dozens of tables and pages of reasoning, he set out the foundation for a water borne theory of cholera.
I’d love to say that the political and medical community accepted the insight with open arms. However, it took time and debate for John Snow’s ideas to eventually overtake the theory of miasma. John Snow didn’t live to see the impact of his thinking. He died of a stroke 16 June 1858, a scant few years after his updated pamphlet on cholera was published. He never lived to see the vast improvements in water quality, and the corresponding reduction in disease brought about by Joseph Bazalgette’s grand sewer project.
All of this makes me think about the current rise of story-driven thinking. Make no mistake, I know that stories are compelling. There is a deserved increase in the focus of how narratives shape our individual lives, those around us and society at large. Under it all though, John Snow’s data-driven investigation is a powerful reminder that a thoughtful exploration of data can yield sometimes confronting new insights. These insights may in turn need a powerful narrative to explain them, but without the data they are just rhetoric.
Though it seems like a disease from another age, cholera still kills between 28,800–130,000 people a year. It is one type of the many waterborne illness that does so. Analysis of modern data suggests that cholera is prevalent in areas where people find it difficult to access clean drinking water. Basically, it affects the people who are lack the funds or resources to access the most basic and humanitarian necessities of life. I wonder what insight we can draw from that.
BBC (2003) Seven Wonders of the Industrial World. BBC Documentary.
Snow, John (1855) On the Mode of Communication of Cholera.