John Snow: the man who understood cholera

2013 is the bicentenary of the birth of John Snow, a pioneer of anaesthetics and epidemiology.  In the 19th century he studied the distribution of cases of cholera in London and inferred that the disease was spread by contaminated water.  This was the first study using the of the distribution of a disease to highlight its cause: we now call this epidemiology and Snow is considered to be the father of this discipline.  Here is what I wrote about him for the Dorset-based Marshwood Vale Magazine:

Cholera is a deadly disease killing more than 100,000 people each year, mostly in the developing world.  Although cholera no longer affects the UK, the mid 19th century saw Britain ravaged by repeated waves of the disease with many thousands dying.  There was little understanding of the disease until John Snow, the Victorian medical pioneer showed how cholera could be contained and prevented; 2013 is the bicentenary of Snow’s birth.

In 1849, a new wave of cholera struck the UK.  Dorset was not spared and Fordington, then a village adjacent to Dorchester, suffered a serious outbreak of the disease.  Fordington was, at that time, a place of great deprivation.  There were many small cottages, mostly without gardens so that all waste, including sewage ended up in the open drain or the Mill Pond.  The Mill Pond was also where most people took water for washing and sometimes for cooking.

Five years later, in 1854, cholera was again on the rampage in the UK.  Millbank prison in London was badly affected and the authorities decided to move seven hundred “uninfected” convicts to a place of safety. Their chosen refuge was a disused cavalry barracks in Fordington.  The Mayor and townsfolk of Dorchester tried hard to resist the move, fearing the consequences, but the convicts duly arrived.  Although attempts were made to minimise contact with the new jail, two women in Fordington contracted to wash bedding from the prisoners. Within days cholera appeared in Fordington and thirty or more people eventually died.  The energetic and intelligent Vicar of Fordington, Henry Moule, worked with the sick and dying, burning contaminated clothing and bed linen, spreading help and sympathy.  He became convinced that poor sanitation was at the root of the spread of the disease.  He recounted how when he sat at the bedside of a dying man, the overflow of one privy shared by thirteen families trickled between him and the bed.  More than 100 miles away, in London, another energetic man, John Snow, had also been thinking about the role of poor sanitation in the spread of cholera.
John Snow

John Snow was born in York in 1813, the eldest of nine children from a poor family.  Snow was determined to be a physician and held three apprenticeships with medical practitioners in the North East where he saw his first cases of cholera.  At the age of 23 he moved to London to continue his medical education, qualifying as a practising physician in 1844.  He became an expert in anaesthetics showing how they could be used more safely and effectively during surgery.  One of his notable patients was Queen Victoria to whom he administered chloroform for pain relief during the birth of two of her children.

Snow was also very interested in infectious diseases.  At the time, the prevailing theory of infection was the “miasma” theory whereby infectious diseases were thought to be spread by poisonous gases emanating from sewers, swamps and decaying organic matter.   Snow did not believe these ideas and wondered if infections might be spread by invisibly tiny organisms.  He applied himself to understanding cholera and during the 1849 outbreak, proposed that the disease was caused by contaminated water.  At the time, no infectious organisms had been identified, so his ideas were not well received.

His greatest insights came during the 1853/4 outbreak.   The west London district of Soho, near where Snow lived, was densely populated; living conditions were poor and sanitation even poorer, reminiscent of Fordington but on a greater scale.  Soho was very badly affected by cholera at this time and many died early in the outbreak.  Snow noticed that many of the deaths occurred in the vicinity of a pump in Broad Street from which local residents obtained water.  He went to the Register Office, checked the records of the victims and found that of the 73 victims who lived close to the pump, 61 drank the water.  The pump became the prime suspect in the search for the culprit which Snow believed was a microbe in the water.  In support of his ideas, he noticed that incidence of cholera was much lower among people in the neighbourhood who used alternative water supplies such as residents of the local workhouse and employees of the local brewery. He convinced the authorities to remove the Broad Street pump handle until the outbreak had subsided.  It was eventually found that a leaking cess pool had been contaminating the water from the Broad Street pump, supporting Snow.  However, despite Snow’s efforts, most people still continued to believe in the miasma theory of infection.

There was, nevertheless, a gradual acceptance that the poor state of sanitation in the capital was a public health risk.   By the 1850s much of London’s sewage was ending up in the Thames which was essentially a very smelly open sewer as well as being the source of drinking water for many.  This was an obvious health hazard whether or not you believed the miasma theory.  Eventually, a vast network of new sewers was built so that the sewage could be diverted downstream of London in to the sea and diseases like cholera disappeared.

Snow died in 1858 and was gradually shown to have been correct about cholera:  in the 1860s, Louis Pasteur showed that diseases could be caused by microorganisms and in 1884 the cholera bacterium was discovered.  Most importantly, Snow was the first person to show that careful mapping of the incidence of a disease, epidemiology, could provide important clues to its cause.  Snow was the father of epidemiology and his work paved the way for other landmark studies such as the demonstration in the 1950s by Richard Doll and Austin Bradford Hill of the link between smoking and lung cancer.

2 thoughts on “John Snow: the man who understood cholera”

    1. Thanks for your comment, Emily, I am glad you enjoyed reading this. It’s good to have feedback.
      Snow’s story is an interesting one and it shows how difficult it is to change entrenched ideas.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s