Tucked away in the lanes of Soho is a typical Victorian pub, complete with wood panelling and wrought-iron lamps, and popular with local office workers and tourists.

Its name, though, is distinctly untraditional. Most people have never heard of the reclusive 19th-century doctor called John Snow, who lived near by, or his connection with the replica water pump on the other side of the street. Yet Snow is now regarded as one of medicine’s most ground-breaking pioneers who cracked the mystery of a deadly disease but whose ideas went unrecognised for nearly 20 years while millions across the world continued to die. My book, The Medical Detective:

John Snow and the Mystery of Cholera, which was this year’s winner of the Medical Journalists’ Association award for communicating medical information to lay people, relates his tale.

His story begins in autumn 1831 when the disease known as cholera morbus, previously unknown in Britain, broke out in the filthy alleys of the Sunderland quayside. By Christmas, it was on its way into Scotland and then south to London and most of England’s towns and cities. Snow was then a 19-year-old surgeon’s apprentice and his first encounter with the disease set him off on a quest to conquer it.

However, when, as a qualified doctor, he tried to interest his colleagues in his theories, he was ignored and then dismissed. The Royal College of Physicians pronounced his work “untenable”, while a group of leading scientists said that after careful inquiry they found nothing to support his views.

That first cholera epidemic killed 32,000 people in Britain. In 1848, 52,000 lost their lives; six years later, 20,000 died. Not until 1866 and after 4,000 more deaths in the East End of London was it finally realised that Snow had been right all along.

Even at a time when deadly epidemics were commonplace, cholera was a shock disease, capable of killing within two to three hours and sometimes striking so fast that its victims collapsed as if hit with a club. The symptoms — violent vomiting, litres of cloudy water pouring from the bowels, cramps that could leave a corpse still twitching after death, dark-blue shrivelled skin and blood turned to thick, black jelly — added to its fearsome reputation. Worst of all, though, was cholera’s habit of exploding without warning, felling hundreds or even thousands simultaneously.

“The cholera was something outlandish, unknown, monstrous,” one doctor recalled. “Its tremendous ravages, so long foreseen and feared, so little to be explained, its insidious march over whole continents, its apparent defiance of all the known and conventional precautions against the spread of epidemic disease, invested it with a mystery and a terror which thoroughly took hold of the public mind and seemed to recall the memory of the great epidemics of the Middle Ages.”

Prevention was impossible because no one could work out how it was spreading. Its long trek from the Ganges delta in India across Asia and Europe, following the travel routes, seemed to indicate that it was contagious, but there were countless cases in which people caring for the sick — breathing their air, washing their bodies, cleaning up their vomit — emerged unscathed. Perhaps the “cholera poison”, as it was called in those pre-Pasteur days, emanated from beneath the earth? Or was it the result of an electrical disturbance, possibly caused by the new railways? Or did its victims succumb because they had too much carbon in their bodies? There were countless theories but many doctors thought “miasma”, the odours given off by rotting organic matter, had to be a culprit.

When the disease broke out in London in 1832, therefore, the surgeon and miasmatist Thomas Calley came up with an ingenious plan. His “ready and easy means of preventing the dreadful destruction” was to disinfect the city’s air by firing off bags of gunpowder from cannons at Greenwich, the Tower of London and the Temple Gardens. Florence Nightingale was a staunch believer in miasmatism. “The very first canon of nursing . . . the first essential to the patient, without which all the rest you can do for him is as nothing . . . is to keep the air he breathes as pure as the external air without chilling him,” she wrote.

But in 1849 Snow uncovered the first clues to this disease when he studied the deaths of two sailors in a back-street dosshouse. He found more evidence in an outbreak at an infamous Victorian child farm, where scores of sick and dying pauper children were discovered four to a bed, lying in their own vomit. Gradually he began to piece together a theory that would eventually explain all of cholera’s maddening contradictions. Then, when 24 residents of a middle-class London street died within days of each other, he found the proof that convinced him he must be right.

The medical establishment, however, obsessed with miasma, refused to listen to this shy loner without money or position.

Snow carried out his definitive piece of research in summer 1854 when he took to the streets of South London and began weeks of door-to-door inquiries to produce the statistics he was sure would put his ideas beyond doubt. In so doing, he founded the modern science of epidemiology. Epidemiologists, known as medical detectives, are concerned with two questions: who gets sick and why? They are at the forefront of the battle to understand and to prevent modern epidemics such as bird flu.