If violence were a stuck problem, it would need new thinking. ‘You have to kind of start over,’ Slutkin said. So he did what any public health researcher would do: he looked at maps and graphs, he asked questions, he tried to understand how violence was happening. And that’s when he started noticing familiar patterns. ‘The clustering seen in maps of killings in US cities resembles maps of cholera in Bangladesh,’ he later wrote.[3] ‘Historical graphs showing outbreaks of killing in Rwanda resembled graphs of cholera in Somalia.’
Susannah eley liked to get her water delivered each day. After her husband had died, she’d moved from the bustle of London’s Soho to leafy Hampstead. But she still preferred the water from the pump in town. She thought it tasted better.
One August day in 1854, Eley’s niece visited her from the neighbouring borough of Islington. Within a week, they would both be dead. The culprit was cholera, an aggressive disease that causes diarrhea and vomiting. Left untreated, up to half of people with severe symptoms will die. The same day that Eley died from cholera, there were 127 other deaths from the disease, most of them in Soho. By the end of September, the outbreak would have claimed over six hundred lives in London. In this era before Koch’s work on germ theory, the biology of cholera was still a mystery. ‘We know nothing; we are at sea in a whirlpool of conjecture,’ wrote Thomas Wakley, founder of The Lancet medical journal, the year before the outbreak started. People were starting to realise that diseases like smallpox and measles were contagious, somehow spreading from person to person, but cholera seemed to be something else. Most believed the ‘miasma theory’, which said that cholera spread through bad smells in the air.[4]
But not John Snow. Originally from Newcastle, Snow had investigated his first cholera outbreak in 1831 as an eighteen-year-old medical apprentice. Even then, he’d noticed some odd patterns. People who should have been at risk from bad air weren’t getting ill, and people who supposedly weren’t at risk were. Snow eventually moved to London, building up a reputation as a talented anaesthetist, with Queen Victoria among his patients. However, when a cholera outbreak hit the city in 1848, he revived his old investigations. Who was catching the disease? When were they getting ill? What linked the cases? The following year, Snow published an article with a new theory: the disease spread from one person to another through contaminated water. The realisation had finally come when he noticed that patients would often share the same water company. It was a remarkable insight, not least because Snow had no idea it was actually microscopic bacteria that were casting cholera’s enormous shadow.
The 1854 Soho outbreak would prove a good match for Snow’s theory. There were the workers at the local brewery, with their diet of ale and imported water, who didn’t get sick. Then there was Susannah Eley and her niece, who had their water shipped from Soho to Hampstead and fell ill. As the outbreak grew, Snow decided it was time to intervene. Public health in Soho fell under the responsibility of a local Board of Guardians. He turned up uninvited at one of their meetings and presented his arguments. The board didn’t fully believe his explanation, but decided to remove the pump handle all the same. The outbreak ended soon afterward.
Three months later, Snow wrote up his theory in more detail. The report included what would become his most famous illustration: a map of Soho, with black rectangles showing each of the cholera cases. The cases clustered around Broad Street, near the pump. It was a pioneering work of abstraction, removing unnecessary details and diversions. Whereas abstract artists like Malevich and Mondrian would later paint blocks of colour to shun reality, Snow’s shapes brought cholera into focus.[5] His rectangles made a previously invisible truth – the source of infection – tangible.
Snow’s updated cholera map of Soho
Credit: John Snow Archive & Research Companion. The mark on the right-hand side is a tear in the original page
Yet on its own, the map was not clear evidence that the water was responsible. If the cholera outbreak had been the result of bad air around Broad Street, the pattern would have looked much the same. So Snow produced a second map, with a crucial addition. As well as plotting the cases, he worked out how long it would take to walk to different pumps, drawing a line to show the places for which the Broad Street pump was nearest. It illustrated the areas that would be most at risk if the pump were to blame. Just as his theory suggested, this was also where most cases were appearing.
Snow would never live to see his ideas vindicated. When he died in 1858, The Lancet published a two-sentence obituary, which failed to mention his work on outbreaks. Like an intellectual miasma, the concept of bad air continued to linger in the medical community.
Eventually the idea of contagious cholera did catch on. By the early 1890s, many had come to accept Robert Koch’s notion of germs that spread disease. Then, in 1895, Koch managed to infect a laboratory animal with cholera.[6] His postulates fulfilled, it was convincing evidence that bacteria was causing the disease, and that cholera was spreading through infected water rather than coming from bad air. Snow had been right.
We now think about infectious diseases in terms of germs rather than miasma, but Gary Slutkin argues that we haven’t made the same progress in our
