Exactly 150 years ago London was in the grip of a cholera epidemic but within the space of a week in early September a doctor changed medical thinking forever.
By Nick Triggle
BBC News Online health staff
Dr Snow was ridiculed for saying cholera was a waterborne disease
Today cholera is indelibly linked with water. However, 150 years ago it was much different.
At the end of August 1854 London's third big cholera outbreak was beginning.
The accepted thinking was that it was an airborne disease.
Within a week London physician John Snow had changed the perceived wisdom - but only after hundreds of people had died.
Dr Snow, who was 41 at the time, had already set out his water theory at conferences in 1849 and 1853 but the medical establishment was still not convinced.
During late August the outbreak was just beginning.
By the end of the month, the disease, which causes severe diarrhoea and vomiting, really took hold with more than 50 cases being reported on the night of 31 August.
During the next four days another 400 came to light.
With the public authorities paralysed by indecision, Dr Snow set about proving he had been right for years.
Analysing the deaths, he soon realised the outbreak was centred around a water pump at the junction of Broad Street, renamed Broadwick Street in 1936, and Cambridge Street in Soho.
He examined it on 3 September but only found minimal evidence of contamination.
Instead, he went to the register of deaths and started to research where the victims lived.
Of the 89 who had died in the first two days of the outbreak all but 10 were served by the pump.
But it was those that did not live near the pump that proved Dr Snow right.
Two ladies from Hampstead, which was five miles away and was not hit by the outbreak, were among the victims.
It turned out that the pair, an aunt and niece, had water regularly transported from the Broad Street pump to drink.
Allied with the information, Dr Snow met with the local parish board of guardians.
On 8 September, in one of the most symbolic gestures in the history of public health, the pump handle was removed and within days new cases had dried up.
A year later the physician published a 139-page text, On the Mode of Communication of Cholera, setting out how the disease spread.
Vibrium cholerae, the cholera-causing bacteria
He paid for the document, an updated version of one he first wrote a few years earlier, out of his own pocket.
Dr Ros Stanwell-Smith, honorary secretary of the John Snow Society, said Dr Snow's work during the first week of September 150 years ago changed the way the world thought about cholera.
"Before he proved it was waterborne, the general opinion was that it came from bad air, the miasma theory.
"Using analytical methods, he was able to demonstrate that it was the sewage contaminating the water that was causing cholera. He probably stopped the second wave of the epidemic.
"For me he is one of the greatest doctors in history. He gave the UK a head start in cleaning up our water supply, which then lead to the developing of the sewage system.
"I guess he was a bit of a maverick, he was ridiculed by some, but stuck to his theory and was proved right."
But for some his legacy goes beyond the field of epidemiology.
He became the first doctor to give a member of the royal family an anaesthetic during the birth of Queen Victoria's son, Prince Leopold, in April 1853.
Cholera: The facts
There are still more than 140,000 cases of cholera a year
The symptoms include severe diarrhoea and vomiting
Rehydration salts and clean water can cure cholera
Cases in the UK are rare, barely more than a handful each year
There have been seven cholera pandemics
The latest started in Indonesia in 1961
Professor Martyn Evans, principal of the John Snow College at the University of Durham, named after the doctor who was born nearby in North Yorkshire, said his expertise crossed several medical fields.
"For us he is an inspirational figure not just for his work in epidemiology but also obstetrics and as an anaesthetist.
"He was one of the country's greatest doctors although he is now more well known in the US than here."
Last year his achievements were recognised when he was voted the greatest doctor of all time in a poll by the Hospital Doctor magazine.
However, it was his work on cholera that remains his lasting legacy.
Dr Snow died before the revolution in public health he had campaigned for for so long took place.
There was another cholera epidemic in 1866 - eight years after his death.
Fellow epidemiologist Dr William Farr, who had at first disputed Dr Snow's theory, provided further evidence water was carrying the disease.
Within years great engineering projects were started in many cities to collect and treat sewage, ultimately eliminating the disease in industrialised countries, including the UK.
A girl takes her first dose of the cholera vaccine in Sudan
A spokeswoman for the Health Protection Agency said: "Cholera is not a really a problem in Britain now. There are only a handful of cases each year and these tend to be brought back by travellers."
However, the disease still remains a killer in the developing world.
The world has been fighting the seventh cholera epidemic since it was identified in Indonesia in 1961.
It soon spread across Asia, Russia and the Middle East and Africa with cholera cases topping 140,000, including 4,500 deaths, in 2002, according to World Health Organisation figures.
The WHO said: "Poor sanitation and food hygiene are the major causes of cholera in the developing world."
And with vaccines now available, the 21st century tragedy is that people are still dying from cholera.
Less than 1 in 100 cases result in death in countries with access to modern medicine but in some third world countries the death rate can top one in two.