A Map Stops Cholera

John Snow's Map of London

A picture of a crowded London street, easy prey for cholera in the 1850s.
'A Court for King Cholera', 1852. A scene typical of the crowded, unsanitary conditions in London slums. Cholera first appeared in Britain in 1831, and outbreaks occurred regularly in London in the mid 19th century. Cartoon from Punch. (London, 25 September 1852). (Photo by Ann Ronan Pictures/Print Collector/Getty Images)

In the mid-1850s, doctors and scientists knew there was a deadly disease called the "cholera poison" rampaging through London, but they weren't sure how it was being transmitted. Dr. John Snow used mapping and other techniques that would later be known as medical geography to confirm that the transmission of the disease occurred by swallowing contaminated water or food. Dr. Snow's mapping of the 1854 cholera epidemic has saved countless lives.

The Mysterious Disease

While we now know that this "cholera poison" is spread by the bacterium Vibrio cholerae, scientists in the early 19th century thought it was spread by miasma ("bad air").  Without knowing how an epidemic spreads, there is no way to stop it.

When a cholera epidemic occurred, it was deadly. Since cholera is an infection of the small intestine, it results in extreme diarrhea. This often leads to massive dehydration, which can create sunken eyes and blue skin. Death can occur within hours. If treatment is given quickly enough, the disease can be overcome by giving the victim a lot of fluids -- either by mouth or intravenously (directly into the blood stream).

However, in the 19th century, there were no cars or telephones and so getting quick treatment was often difficult. What London -- and the world -- really needed was someone to figure out how this deadly disease spread.

The 1849 London Outbreak

While Cholera has existed in Northern India for centuries --  and it is from this region that regular outbreaks are spread -- it was the London outbreaks that brought cholera to the attention of British physician Dr. John Snow.

In a 1849 cholera outbreak in London, a large proportion of the victims received their water from two water companies.

Both of these water companies had the source of their water on the Thames River, just downstream from a sewer outlet.

Despite this coincidence, the prevailing belief of the time was that it was "bad air" that was causing the deaths. Dr. Snow felt differently, believing that the disease was cause by something ingested. He wrote down his theory in the essay, "On the Mode of Communication of Cholera," but neither the public nor his peers were convinced.

The 1854 London Outbreak

When another cholera outbreak hit the Soho area of London in 1854, Dr. Snow found a way to test his ingestion theory.

Dr. Snow plotted the distribution of deaths in London on a map. He determined that an unusually high number of deaths were taking place near a water pump on Broad Street (now Broadwick Street). Snow's findings led him to petition the local authorities to remove the pump's handle. This was done and the number of cholera deaths was dramatically reduced.

The pump had been contaminated by a dirty baby diaper that had leaked the cholera bacteria into the water supply.

Cholera Is Still Deadly

Although we now know how cholera is spread and have found a way to treat patients who have it, cholera is still a very deadly disease.

Striking quickly, many people with cholera don't realize how serious their situation is until it is too late.

Also, new inventions such as airplanes have aided the spread of cholera, letting it surface in parts of the world where cholera has otherwise been eradicated.

According to the World Health Organization, there are up to 4.3 million cases of cholera each year, with approximately 142,000 deaths.

Medical Geography

The work of Dr. Snow stands out as one of the most famous and earliest cases of medical geography, where geography and maps are utilized to understand the spread of a disease. Today, specially trained medical geographers and medical practitioners routinely use mapping and advanced technology to understand the diffusion and spread of diseases such as AIDS and cancer.

A map is not just an effective tool for finding the right place, it can also save a life.