Monday, December 10

John Snow versus The Miasma UPDATED 6:05 AM ET

Miasma Theory of Cholera (bad air)

John Snow's map showing the cluster of cholera cases in the London epidemic of 1854

It's been an uplifting experience for me to learn about the doctors who took on the Miasma theory of disease to battle mass-death epidemics to a standstill; I hope it's been the same for those who've been reading my recent posts on the topic. Now to John Snow.

John Snow (15 March 1813 – 16 June 1858 was an English physician and a leader in the adoption of anaesthesia and medical hygiene. He is considered one of the fathers of modern epidemiology, in part because of his work in tracing the source of a cholera outbreak in Soho, London, in 1854. His findings inspired fundamental changes in the water and waste systems of London, which led to similar changes in other cities, and a significant improvement in general public health around the world. [...]
From two other Wikipedia articles:

The Broad Street cholera outbreak (or Golden Square outbreak) was a severe outbreak of cholera that occurred in 1854 near Broad Street (now Broadwick Street) in the Soho district of the City of Westminster, London, England, and occurred during the 1846–1860 cholera pandemic happening worldwide. This outbreak, which killed 616 people, is best known for the physician John Snow's study of its causes and his hypothesis that germ-contaminated water was the source of cholera, rather than particles in the air (referred to as "miasmata"). 
This discovery came to influence public health and the construction of improved sanitation facilities beginning in the mid-19th century.
Later, the term "focus of infection" started to be used to describe sites, such as the Broad Street [water] pump, in which conditions are good for transmission of an infection. Snow's endeavor to find the cause of the transmission of cholera unwittingly created a double-blind experiment.
From Germ Theory of Disease/John Snow: 

John Snow was a skeptic about the then-dominant miasma theory. Even though the germ theory of disease pioneered by Girolamo Fracastoro had not yet achieved full development or widespread currency, Snow demonstrated a clear understanding of germ theory in his writings. 
He first published his theory in an 1849 essay On the Mode of Communication of Cholera, in which he correctly suggested that the fecal-oral route was the mode of communication, and that the disease replicated itself in the lower intestines. He even proposed, in his 1855 edition of the work, that the structure of cholera was that of a cell.
[quotes from his essays]
Snow's 1849 recommendation that water be "filtered and boiled before it is used" is one of the first practical applications of germ theory in the area of public health and is the antecedent to the modern boil-water advisory.
In 1855 he published a second edition of his article, documenting his more elaborate investigation of the effect of the water supply in the Soho, London epidemic of 1854.
By talking to local residents, he identified the source of the outbreak as the public water pump on Broad Street (now Broadwick Street). Although Snow's chemical and microscope examination of a water sample from the Broad Street pump did not conclusively prove its danger, his studies of the pattern of the disease were convincing enough to persuade the local council to disable the well pump by removing its handle. This action has been commonly credited as ending the outbreak, but Snow observed that the epidemic may have already been in rapid decline.
Snow later used a dot map to illustrate the cluster of cholera cases around the pump. He also used statistics to illustrate the connection between the quality of the water source and cholera cases. He showed that the Southwark and Vauxhall Waterworks Company was taking water from sewage-polluted sections of the Thames and delivering the water to homes, leading to an increased incidence of cholera.
Snow's study was a major event in the history of public health and geography. It is regarded as one of the founding events of the science of epidemiology.
Later, researchers discovered that this public well had been dug only three feet from an old cesspit, which had begun to leak fecal bacteria. The diapers of a baby, who had contracted cholera from another source, had been washed into this cesspit. Its opening was originally under a nearby house which had been rebuilt farther away after a fire. The city had widened the street and the cesspit was lost.
It was common at the time to have a cesspit under most homes. Most families tried to have their raw sewage collected and dumped in the Thames to prevent their cesspit from filling faster than the sewage could decompose into the soil.
After the cholera epidemic had subsided, government officials replaced the handle on the Broad Street pump. They had responded only to the urgent threat posed to the population, and afterward they rejected Snow's theory. To accept his proposal would have meant accepting the fecal-oral method transmission of disease, which they dismissed.
They dismissed it because they still clung to the Miasma theory of disease -- against evidence piled up over centuries indicating the theory was nonsense. But how, then, did his findings inspire "fundamental changes in the water and waste systems of London"? To return to Wikipedia's biographical article about Dr Snow:
... It wasn't until 1866 that William Farr, one of Snow's chief opponents, realized the validity of his diagnosis when investigating another outbreak of cholera at Bromley by Bow and issued immediate orders that unboiled water was not to be drunk.

Farr denied Snow's explanation of how exactly the contaminated water spread cholera, although he did accept that water had a role in the spread of the illness. In fact, some of the statistical data that Farr collected helped promote John Snow's views.

Public health officials recognise the political struggles in which reformers have often become entangled. During the Annual Pumphandle Lecture in England, members of the John Snow Society remove and replace a pump handle to symbolise the continuing challenges for advances in public health. ...


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