medical history

The DO Book Club, June 2020: The Ghost Map: The Story of London’s Most Terrifying Epidemic

Dr. John Snow’s discovery that bacteria-contaminated water caused cholera saved countless 19th-century Londoners and changed public health forever.


Welcome back to The DO Book Club! For June, I read The Ghost Map: The Story of London’s Most Terrifying Epidemic — and How it Changed Science, Cities and the Modern World by Steven Johnson. If you’ve read this one, please share your thoughts in the comments below. And if you’d like to write a book review for a future month, please email Andy Brown at

Plot summary

In the early 1850s, London had extremely population-dense living conditions, which came with high levels of human waste. Getting rid of that waste was a cost only some could afford, which led to “artificial ponds of raw sewage” (p. 11) that frequently accumulated, and even overflowed, in working-class neighborhoods.

Recurring cholera outbreaks were a natural consequence of these living conditions, but at that time, their cause was a source of major debate. Most scientists and physicians incorrectly believed cholera could be traced to rancid smells, but Dr. John Snow, who also played a major role in the development of modern anesthesiology and medical hygiene, was convinced that bacteria-contaminated water was to blame after rigorously studying stool samples and sewage records for years.

In 1854, Dr. Snow’s theory finally reached the surface. A mother washed her baby’s used diaper in a bucket of water, then dumped the bucket in a sewage pond near her house, which fed into the area’s primary well. Hundreds who pumped their water from there soon fell ill, and 616 eventually died.

We know the cause to this level of detail thanks to the tireless efforts of Dr. Snow. He approached the problem from a bird’s-eye view, examining the patterns of those that lived near the well and became ill or died. The map he put together, marking as many deaths and cases as he could, told an abundantly clear story. It showed that cholera cases radiated from a single point, directly following patterns of street traffic: the contaminated well.

This overwhelming evidence was enough to convince the London Board of Governors to cut off public access to the well, which undoubtedly saved thousands of lives. Sadly, Dr. Snow passed away just four years later and did not live to see the full impact of his work, both locally (a decade later, London completely redesigned its water and waste system), and globally (his methods provided the foundation of modern disease tracking, and have often been replicated with great success).

Interesting tidbits for DOs

Johnson provides many interesting details on the epidemiology of cholera, explaining how the bacteria that causes it, V. cholerae, following unconscious, adaptive instincts, alters its approach to attacking its host based on the possibility for transmission nearby.

“In environments where the risk of transmission is low, the better strategy is to pursue a low-intensity attack on the human host: reproduce in smaller numbers, and keep the human alive longer, in hopes that over time some bacterial cells will find their way to another intestine. … A dense urban settlement with contaminated water supplies eliminates V. cholerae’s dilemma. There’s no incentive not to reproduce as violently as possible—and thus kill your host as quickly as possible—because there’s every likelihood that the evacuations from the current host will be swiftly routed into the intestinal tract of a new one” (p. 43).

He also provides a grim look at the quality of medical communications in the 1850s. Doctors would often make definitive, yet confusing public statements with little sign of any peer review. Remember from January’s Book Club that for much of the 19th century, most physicians didn’t believe germs existed. And none of these statements provided the simple advice all cholera patients needed: rehydrate.

One letter to the editor of a London newspaper illustrates the public’s frustration:

“If the doctors who write to the papers would agree in their prescriptions for cholera, the public might feel grateful for the trouble taken, but when one medical man’s ‘infallible medicine’ is another man’s ‘deadly poison,’ and the specific of to-day is denounced as the fatal drug of tomorrow, we are puzzled and alarmed at the risk we run in following the doctors’ contradictory directions” (p. 50).

Notable quotes

Though Johnson’s book covers a significant leap in medical knowledge, his perspective on the blind spots that often predate advances is thought-provoking:

“The history of knowledge conventionally focuses on breakthrough ideas and conceptual leaps. But the blind spots on the map … carry their own mystery as well. How could so many intelligent people … ignore so much overwhelming evidence that contradicted their most basic theories? These questions, too, deserve their own discipline—the sociology of error” (p. 15).

Johnson’s insights on the historical significance of epidemics are also compelling, especially right now, while we’re grappling with a global pandemic:

“Most world-historic events are self-consciously historic to the participants living through them. They act knowing that their decisions will be chronicled and dissected for decades or centuries to come. But epidemics create a kind of history from below: they can be world-changing, but the participants are almost inevitably ordinary folk, following their established routines, not thinking for a second about how their actions will be recorded for posterity” (p. 32).


I was a little disappointed by how the book was organized. It was a very compelling story that will make any reader think, regardless of their experience level in medicine. For that reason alone, I recommend it. But Johnson went down a few too many rabbit holes on urbanization and false cholera theories for my liking, when I was hoping for a deeper dive into the incredible life of Dr. Snow.

That said, outside of a book on the 1918 influenza pandemic (which this book club may someday read—stay tuned!), I think you’d be hard-pressed to find an easy-reading history book better suited for COVID-19. 166 years later, this incredible story is proof that even if things seem bleak and unsolvable, there is always room for medical innovation.

July’s book

For July, The DO Book Club will be reading The Body Keeps the Score: Brain, Mind, and Body in the Healing of Trauma by Bessel A. van der Kolk, MD. We encourage all who are interested to read along! If you are unable to get out to a local library or bookstore due to COVID-19, we recommend checking out eBook options for rent or purchase.

As a reminder, if you read The Ghost Map or any previous Book Club selection and want your reflections to be shared in future posts, or want to write your own book review for a future month, please leave a comment below or email

Happy reading!

Related reading:

The DO Book Club, May 2020: This is Going to Hurt: Secret Diaries of a Medical Resident

The DO Book Club, April 2020: The Body: A Guide for Occupants

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