John Snow (15 March 1813 – 16 June 1858) was a British physician and a leader in the adoption of anaesthesia and medical hygiene. He is considered to be one of the fathers of epidemiology, because of his work in tracing the source of a cholera outbreak in Soho, England, in 1854.
Snow studied in York until the age of 14, when he was apprenticed to William Hardcastle, a surgeon in Newcastle-upon-Tyne and physician to George Stephenson and family. William Hardcastle was a friend of Snow's uncle, Charles Empson, who was both a witness to Hardcastle's marriage and executor of his will. Charles Empsom also went to school with Robert Stephenson and it was probably through these connections that Snow acquired his apprenticeship so far from his home town of York. Snow later worked as a colliery surgeon. Between 1833 and 1836 he was an assistant in practice, first in Burnopfield, Durham, and then in Pateley Bridge, North Yorkshire. In October 1836 he enrolled as a student at the Hunterian school of medicine in Great Windmill Street, London. A year later, he began working at the Westminster Hospital and was admitted a member of the Royal College of Surgeons of England on 2 May 1838. He graduated from the University of London in December 1844, and was admitted to the Royal College of Physicians in 1850.
Snow was a skeptic of the then-dominant miasma theory that stated that diseases such as cholera or the Black Death were caused by pollution or a noxious form of "bad air". The germ theory was not widely accepted at this time, so he was unaware of the mechanism by which the disease was transmitted, but evidence led him to believe that it was not due to breathing foul air. He first publicized his theory in an essay On the Mode of Communication of Cholera in 1849. In 1855 a second edition was published, with a much more elaborate investigation of the effect of the water-supply in the Soho, London epidemic of 1854.
By talking to local residents (with the help of Reverend Henry Whitehead), 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 sample of the Broad Street pump water was not able to 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. Although this action has been popularly reported as ending the outbreak, the epidemic may have already been in rapid decline, as explained by Snow himself:
Snow later used a spot map to illustrate how cases of cholera were centred around the pump. He also made a solid use of statistics to illustrate the connection between the quality of the source of water and cholera cases. He showed that companies taking water from sewage-polluted sections of the Thames delivered water to homes with an increased incidence of cholera. Snow's study was a major event in the history of public health, and can be regarded as the founding event of the science of epidemiology.
In Snow's own words:
It was discovered later that this public well had been dug only three feet from an old cesspit that had begun to leak fecal bacteria. A baby who had contracted cholera from another source had its diapers washed into this cesspit, the opening of which was under a nearby house that had been rebuilt farther away after a fire had destroyed the previous structure, and the street was widened by the city. 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.
Public health officials today recognize the political struggles that reformers often get entangled in. During the Annual Pumphandle Lecture in England, members of the John Snow Society remove and then replace a pump handle to symbolize the continuing challenges that face public health advancements.
There is a plaque commemorating Snow and his 1854 study in the place of the water pump on Broad Street (now Broadwick Street) with a water pump with its handle removed, near what is now "The John Snow" public house, which is rather ironic, given that Snow was a teetotaler for the majority of his life. The spot where the pump stood is covered with red granite.
In York, there is a blue plaque to Snow on the west end of the Park Inn, a hotel in North Street.
John Snow was voted in a poll of British doctors in 2003 as the greatest physician of all time.
Snow is one of the heraldic supporters of the Royal College of Anaesthetists.
The public health consulting firm John Snow, Inc is named after him.