Social DataViz: Cholera is Still With Us 165 Years after the 1854 Cholera Epidemic in London

Readers:

Back in 2013, I did a multi-blog post on the 1854 cholera epidemic in London. Most of the reference material I used was based on Steven Johnson’s riveting book, The Ghost Map: The Story of London’s Most Terrifying Epidemic–and How It Changed Science, Cities, and the Modern World (see book cover below)

What I want to discuss today are three key topics.

1. The World has Left Yemen to Die, which is excerpted from an article in National Geographic written by Nina Strochlic, a staff writer covering culture, adventure, and science for National Geographic magazine. And, Matteo Bastianelli, a documentary photographer, and filmmaker based in Rome, Italy. Many of his long-term projects center on the consequences of war. This is an exclusive story and photos which gives a rare look inside the country of Yemen, where civil war has trapped civilians in a life of violence and disease. [1]
2. I will revisit John Snow’s now famous Ghost Map, which showed how Dr. John Snow and Reverend Henry Whitehead were able to pinpoint the cause of the cholera epidemic in 1954 London. I will discuss the breakthroughs made by John Snow, but also discuss what he was not able to achieve. [2]
3. Finally, I will discuss the other less known mapping of cholera in England in 1854. This was excerpted from the book, All Over the Map, A Cartographic Odyssey, by Betty Mason and Greg Miller. The book discusses physician Henry Wentworth Acland who tracked an outbreak in Oxford that affected 290 people that year. His work, which resulted in the 170-page Memoir on the Cholera at Oxford and an accompanying map, was “perhaps the most comprehensive study of an urban disease of its day,” according to Koch. [3]
   

Best Regards,

Michael

Note: See references to the source material at the end of this blog post.

The World Has Left Yemen to Die (National Geographic)

In 2019, 165 Years after the 1854 cholera epidemic in London, which produced the now legendary Ghost Map, cholera still exists in our world. Since 2017, Yemen has seen more than a million suspected cholera cases—the worst outbreak in modern history (see the two maps from National Geographic below). [1] One NGO ordered a shipment of medication in July 2017. It didn’t arrive until April 2018.

In Yemen, doctors and other health workers at public hospitals haven’t been paid since 2016. Humanitarian groups are supporting the health ministry with salaries and supplies. But a Saudi-led coalition blockade on the country’s airports and ports in an attempt to stop supplies from reaching the rebels has arbitrarily delayed or diverted aid shipments, says Kristine Beckerle, with Human Rights Watch, adding that both sides “are weaponizing aid.”

If you are dying, one elderly man told Bastianelli, you have to pay to be pronounced dead.

Many of Yemen’s doctors have moved to private hospitals or fled the country, leaving a shortage of medical professionals. Those who stay behind train their neighbors to treat wounds in case of an emergency overnight, when it’s too dangerous to travel. The private clinics cost more than even a middle-class civilian can afford. If you are dying, one elderly man told Bastianelli, you have to pay to be pronounced dead. The other option is to drive across the front lines to one of the country’s two open airports. Few can afford the cost of fuel—or the risk. “They’re locked in Yemen. No country is giving them asylum or making a humanitarian corridor,” says Bastianelli. “They count the days and wait to die.”

The Ghost Map: The Story of London’s Most Terrifying Epidemic–and How It Changed Science, Cities, and the Modern World.

In 1831, cholera hit the United Kingdom and began killing tens of thousands during successive waves of terrifying outbreaks. The disease was fatal for as many as a quarter of its victims, often within just days of exposure. Many scientists of the day embraced the theory that epidemics were caused by the foul air, or miasma (from open cesspools, raw sewage, and rotting rubbish), that hung over large swaths of most major cities. Many people believed that cholera was an airborne disease that you contacted from breathing the air. An English doctor named John Snow documented an outbreak of cholera in his London neighborhood in 1854 that contradicted this theory.

Dr. Snow, with the help of Reverend Henry Whitehead, carefully mapped the locations of the victims’ homes and demonstrated that the deaths were clustered around a public water pump on Broad Street in the Soho district. By interviewing the victims’ families, they were able to trace nearly every case back to that water pump, bolstering Snow’s theory that cholera is a waterborne disease and convincing the local authorities to remove the pump’s handle. The story has become legendary, and Snow’s map is often portrayed as a breakthrough moment in both cartography and epidemiology.

However, history can be cruel in the way the truth is told. Dr. Snow did indeed do excellent work that helped advance the science, and his map still rightfully stands as a shining example of medical cartography. But it wasn’t until long after Snow’s death in 1858 that his theory was proved correct and his work was hailed as a turning point. “His map has become an icon and Snow himself an almost mythic figure,” writes medical geographer Tom Koch in Cartographies of Disease. “Few focus, therefore, on Snow’s failure to convince his contemporaries of his argument (Miasma Theory where it was an airborne disease versus Snow’s theory that cholera was a waterborne disease), the limits of his thesis in the context of his time.”

Dr. Snow wasn’t the only one mapping cholera in England in 1854. The physician Henry Wentworth Acland tracked an outbreak in Oxford that affected 290 people that year. His work, which resulted in the 170-page Memoir on the Cholera at Oxford and an accompanying map, was “perhaps the most comprehensive study of an urban disease of its day,” according to Koch.

The Topography of Disease

Many experts found Acland’s work more convincing than Snow’s, partly because of its breadth and thoroughness. But Acland’s research had another big advantage: Its conclusions supported the prevailing miasmatic theory of disease, which had been developed over centuries. Snow, on the other hand, was bucking the mainstream with his waterborne-disease theory.

While Snow’s analysis was focused on one possible explanation for the outbreak (it was a waterborne disease), and his argument rested on the visual clarity of his map, Acland took a more statistical approach that considered many potential disease factors. In addition to mapping victims, Acland included sites that had previously been deemed unhealthy (brown dots), those that had subsequently been cleaned up (brown circles), streams that were unpolluted, and those that had been contaminated (dashed lines), including point sources of the contamination such as outflows of raw sewage (see map below). Areas with poor drainage were shaded green.

Dr. Snow was content to stop mapping the cholera deaths that occurred after he thought his case had already been made. By contrast, Acland mapped the entire list of victims in 1854, as well as those of two previous outbreaks. He used different symbols for the locations of victims’ homes from 1832 (blue dots), 1849 (blue bars) and 1854 (black squares and bars). And, most important for his argument, Acland mapped the physical topography of the town with five-foot (1.5 meters) contour lines. His map, together with his statistical analysis, showed a clear correlation between elevation and the disease. In each of the three outbreaks, people in low-lying areas suffered a much higher rate of infection and death. Even the higher spots that had unhealthy brown dots fared better than the lowlands.

Acland failed to see the whole picture, making his a cautionary tale, she (Este Geraghty) says. “You have to determine what things mean, not just the outcome and the correlation.”

Acland’s map neatly backed up the miasmatic theory, suggesting that the toxic air would collect and remain in low areas with less wind. “His statistics are showing that he had an excellent argument and evidence,” says Este Geraghty, chief medical officer for the mapping software company Esri. But Acland failed to see the whole picture, making his a cautionary tale, she says. “You have to determine what things mean, not just the outcome and the correlation.” As data visualization journalist Alberto Cairo has noted in numerous presentations of his I attended, “Correlation does not necessarily equal causation.” I fondly remember he once said, “The sending of Christmas cards does not cause Christmas to occur.”

Note: Cairo is also the Knight Chair in Visual Journalism at the School of Communication of the University of Miami.

Acland saw polluted water as a potential contributor to pestilent air, not as a medium for the spread of an invisible agent of disease. Consequently, he hadn’t paid attention to sources of drinking water. Instead, like many of his contemporaries, he looked to the weather for clues to how elevation could be influencing the disease.

“That there is a connection between the state of the Atmosphere, or of the imponderable agents of the globe, and the existence of the Epidemic, is scarcely doubted by those who have carefully attended to its history,” he wrote.

Acland meticulously charted the timeline of the 1854 outbreak against a host of local climate variables, including temperature, barometric pressure, wind, rain, humidity, cloud cover and ozone levels (below). But he was unable to find anything that waxed and waned precisely with the number of new cholera cases. What Acland was able to demonstrate, with copious data, is that 1854 was an abnormal year for weather in Oxford. Comparing it with the 25 years prior, he found that rain was abnormally low, as was wind speed. The list of things that were abnormally high included temperature range, pressure, thunder and lightning, days with hail, and appearances of the northern lights.

He couldn’t quite put any of these variables together with elevation to form a reasonable explanation, especially considering that the previous outbreaks didn’t follow the same pattern. But Acland was still confident that if another epidemic were to occur, “the rapidly advancing science of Meteorology” would be able to use data to clarify which of the abnormalities played a role.

Acland’s study was more comprehensive, and, at the time, more convincing than Snow’s, but it had one glaring flaw: His conclusion was definitively wrong.

Acland’s study was more comprehensive, and, at the time, more convincing than Snow’s, but it had one glaring flaw: His conclusion was definitively wrong. “Like much of the science of every era, it missed an intervening vector,” Koch writes. What Acland failed to see was that at higher elevations, water typically came from wells or streams, while lower areas mostly relied on rivers that were often polluted with sewage. But, Koch notes, “the mapping—and here, the mapmaking—were clear, consistent, and, if ultimately incorrect, still rigorous.”

Snow’s theory was largely dismissed during his lifetime, but he ultimately triumphed long after his death. Conversely, Acland enjoyed recognition from his peers for his work on cholera but lived to see the theory it supported disproved. Still, his work is worth more than a footnote, argues Alberto Cairo.

“The myth of the hero who singlehandedly wrecked miasmatic theory obscures the fact that those who held onto it were also thoughtful fellows,” Cairo writes. “It is unfortunate that we don’t study them further, as we humans learn much more from our mistakes—both individual and collective—than from our successes.”

Sources:

[1] Nina Strochlic and Matteo Bastianelli, The World Has Left Yemen to Die, National Geographic Magazine, August 2018, https://www.nationalgeographic.com/magazine/2018/08/dispatches-yemen-health-crisis/.

[2] Steven Johnson, The Ghost Map: The Story of London’s Most Terrifying Epidemic–and How It Changed Science, Cities, and the Modern World, Riverhead Books, October 2, 2007, ISBN: 1-59448-925-4.

[3] Betty Mason, The Topography of Disease – A 19th-century doctor famously mapped cholera’s toll to try and understand its origin and spread—but that’s only part of the story, Scientific American, January 29, 2019, https://blogs.scientificamerican.com/observations/the-topography-of-disease/.