Lessons from the ghost of John Snow

200 years ago this week, John Snow was born. Here at Public Health Perspectives, we’re pretty big fans of his.

If I’da known you were coming, I’da baked a cake

Stephen Johnson, who wrote a book about Snow’s 1854 cholera investigation called The Ghost Map, walks us through the story in a TED talk. Go ahead and watch. I’ll wait.

Snow has been called the father of modern epidemiology, and his map praised by no less than Edward Tufte. His story wasn’t remarkable in any single respect (he wasn’t even the first to map cholera deaths in Victorian London) but it brings together so many important aspects of public health that we’re still learning from today. Here are my top three:

1. Data visualizations can make powerful arguments for change

In 1854, the same year as Snow’s cholera outbreak, war broke out in the Crimean peninsula. Florence Nightingale was a nurse to the wounded there, and created these famous polar area diagrams depicting causes of death among the soldiers. Preventable diseases dwarfed battle wounds in mortality:

Florence Nightingale’s depiction of causes of mortality among soldiers. Blue represents deaths from preventable disease, red from wounds, black from other causes.

John Maindonald writes in the Journal of Statistics Education that Nightingale “made strong, consistent and carefully argued cases for enlightened and data-based public decision-making.” The charts were a big part of that.

Today, we rely on visualizations like Snow’s. The World Health Organization has a big pile of cholera maps, and it’s totally no big deal. Disease mapping is still fertile ground for innovation, though: doctors can now mark patients on outbreak maps with their iPhones, and social media can be data-mined to show how disease spreads.

2. Microbes have been under our nose all this time

While John Snow was arguing that there was something harmful in the water on Broad Street, Filippo Pacini was staring through his microscope in Italy at the germ later named Vibrio cholerae.


Vibrio cholerae

Although we got a pretty good handle on pathogens in the 19th century, we’re still learning about the good guys under the microscope. The Human Microbiome Project is one major effort to figure out just what species we’re carrying around, whether we all carry the same ones (and, if not, what the differences mean) and what all this has to do with our health.

We now have evidence that microbes regulate blood pressure, contribute to obesity, affect brain function, and train our immune systems, just to name a few. The ones that cause or prevent acne are literally under our nose.

3. Sanitation and clean water are (still!) really important.

Many of the world’s worst diseases are passed through the fecal-oral route. It’s the way those germs evolved: get the host to poop you out, and you’re on your way toward a free ride into the next person’s gut.

Preventing that mode of transmission means separating the water you drink (and the food you eat) from, as Water.org delicately puts it, “yesterday’s dinner.” Billions of people lack adequate sanitation. According to Water.org’s numbers, more people worldwide have a cell phone than a toilet, and diarrheal diseases kill more children than malaria, AIDS, and measles combined.

Stephen Johnson mentions in his talk that when cholera next broke out in London, officials told those in the affected area to boil their water; sewers were already under construction. That, he says, was the last major outbreak in the city.

Today, the challenge is getting clean water to, and waste away from, people mainly in rural areas in developing countries. Among the newest efforts: the Sanitation App Challenge (winners to be announced next week). Contenders include apps like the Trashmaster and the Ladies Room Finder.


The difference between now and 1854 is: we’re aware of all this stuff. We have giants’ shoulders to stand on. And yet, the supply of public health puzzles is probably infinite. So let’s get back to work after toasting the man who made, as Stephen Johnson put it, “a map of deaths that ended up creating a whole new way of life.”

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Lessons from the ghost of John Snow by Public Health, unless otherwise expressly stated, is licensed under a Creative Commons Attribution 3.0 Unported License.

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2 Responses to Lessons from the ghost of John Snow

  1. Pingback: John Snow, data journalist | Simon Rogers

  2. Lisa Hirsch says:

    That’s Steven Johnson, not Stephen; otherwise, great posting and very informative.

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