Issue 3 Article 2

Dr John Snow and the Curious Case of the Water Pump Poisonings

25/3/20

By:

Lee Zhe Yu, Nathan

Edited:

Wu Yuxuan

Tag:

Anatomy and Pathology

It is the mid-19th century, and a large wave of immigrants is settling into London. This is particularly problematic for the Soho district, as the city’s sewer system has not yet reached the area. Consequently, the rudimentary sewage system becomes contaminated with animal droppings and rotting fluids from the various cowsheds and slaughterhouses that line the streets. With wastes overflowing from the sewers, the London government decided to dump the waste into the River Thames. This contaminated water supply caused cholera outbreaks in 1839 and 1842 that claimed more than 14000 lives.

Two Main Theories

At that time, there were two main schools of thought regarding what caused cholera in humans. One was the miasma theory, which purported that “bad air” consisting of contaminated particles from decomposing matter and / or other dirty organic sources was to blame for cholera. A proponent for this theory was Dr William Farr, the commissioner for the 1851 London census and a member of the General Register's Office. He claimed that miasmatic particles were released from the soil around the River Thames by decaying organic matter into the London air, causing cholera.

On the other hand, germ theorists believed that cholera was principally caused by a germ cell that had not been identified yet. Our main protagonist of this story, Dr John Snow, was a fierce advocate for this theory, hypothesising that a disease-causing agent was transmitted through the consumption of contaminated water. Despite his conviction, germ theory had not been officially proposed yet, with Louis Pasteur only doing so in 1861.

His ideas did not receive universal acclaim, however. Other than the aforementioned Dr Farr, another John, Sir John Simon, was a notable critic. While displaying an understanding for John Snow’s ideas, the pathologist and the lead medical officer for London was doubtful about its link to cholera.

Already Proven

Actually, scientific proof of Dr John Simon’s idea had emerged the year that tragedy struck -- 1854. That was also the year when Italian physician Dr Filippo Pacini discovered the bacterium Vibrio cholerae, the pathogen that causes cholera. Unfortunately, the then-dominant miasma theory prevented its acceptance in the scientific community, despite it being effective proof of the germ theory.

Tragedy

On 31 August 1854, after a year riddled with cholera outbreaks, “the most terrible outbreak of cholera which ever occurred in this kingdom”, quoting Dr John Snow, happened in Soho. 127 people on or near Broad Street died within the next 3 days, and around 75% of the area’s residents fled during the next week. By 10 September 1854, more than 500 people had died and in some parts of Soho the mortality rate reached 12.8 deaths per 1000 people, which correlates to 1.28%. At the end of the outbreak, 616 people had met their demise.

The Hero Acts

In the midst of the loss and tragedy, Dr John Snow set himself to the task of tackling the root of the problem. He identified the main source of contamination to be the Broad Street public water pump at Cambridge Street after conversing with local residents. In addition, on 61 occasions he was informed that the cholera victim used to drink water occasionally or constantly from the Broad Street water pump. While his analysis of the patterns of illness and death exhibited by the Soho residents were convincing enough for the local authorities to disable the water pump, his chemical and microscope examination of a water sample was unable to conclusively prove its danger.

Data and Stats

Undeterred, he proceeded to create a dot map of how the cholera cases occurred around the pump. His efforts to connect the cholera cases with potential geographic sources resulted in a diagram now known as a Voronoi diagram*, which partitions a plane area into different regions based on their proximity to each selected point (in this case, water pumps). This allowed him to identify the closest water pump to each cholera case. From his diagram, he was able to conclude that the areas in the city where the Broad Street pump was the closest available source of water included those with the highest incidence of cholera cases.

Holes in the Theory

However, his theory suffered a slight snag. The Workhouse at Poland Street, used for housing inmates, suffered a shockingly low death rate of 5 out of 535 inhabitants to cholera despite being 75% surrounded by houses with cholera victims. To complicate matters further, the Broad Street brewery near the water pump registered no deaths out of its seventy-men strong workforce.

Explaining the abnormalities

Upon further investigation, however, Dr John Snow was able to resolve both these peculiarities. First, the Workhouse at Poland Street had its own pump well to complement the supply of water from other waterworks, and hence the inmates were never sent to the Broad Street pump for water. Hence, they did not consume water from the main contamination site, resulting in a correspondingly low death rate. Next, the workers at the Broad Street brewery received an allowance from the beer brewed from the brewery, which had its own water well. To brew the beer, the water would have undergone a boiling process, and the bacterium would have thus been killed at the high temperatures. The resulting beer would hence be safe to drink. With the workers solely relying on beer rather than water from the public pumps, they unsurprisingly remained cholera-free. In short, the outbreak of cholera was contained to the people who drank water from the aforementioned public pump.

A disappointing ending

With the dominance of the miasma theory at that time, it was almost inevitable that government officials would reject Dr John Snow’s theory. Socially, it would have been untenable to convey to the public that cholera was transmitted orally via consumption of faecal matter, and scientifically, the lack of understanding of statistical methods meant that his results were not easily understood. Another outbreak of cholera occurred soon afterwards, and Dr John Snow once again proved that contaminated water was the cause of the outbreak again. The Board of Health had conducted their own investigations and found evidence of “vibriones”, or particles, in water. Despite doing so, the Board of Health concluded that these vibriones did not cause cholera and attributed the 1854 cholera outbreak to miasma.

Modern Impact

This understanding of the germ theory precipitated the development of public health infrastructure. With diseases being attributed to specific pathogens rather than general foul air, the importance of robust public health systems and proper sewage treatment was highlighted. This led to significant public health reform that resulted in improved urban sanitation and reduced the occurrence of water-borne diseases in cities, including London.

In addition, his methodology of using statistical data analyses and hypothesis testing continue to be used in modern epidemiology. Today, from Mpox to COVID-19, Dr John Snow’s principles still remain fundamental in studies tracking such infectious disease outbreaks.

Redemption, in a way

It was only in 1883 when international recognition for the definitive identification and growth of a cholera-causing pathogen was given, to the eminent German epidemiologist Robert Koch11. With the germ theory proven and the miasma theory disproved, Dr John Snow’s work eventually received recognition as a founding event of epidemiology during the following years. However, by that time, the man himself was long dead, having suffered a stroke in 1858 aged 45.

*Today, Voronoi Diagrams are used in various fields, from designing windows, to crystal growth and modelling animal territories.

References:

Image Credit

https://en.wikipedia.org/wiki/File:Snow-cholera-map-1.jpg

Issue 4 - Apr 2025

Dr John Snow and the Curious Case of the Water Pump Poisonings