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Getting a Handle on Public Health

Friday, February 16, 2007

Steven Johnson’s new book shows how we beat cholera, and what we can learn from the experience.

Ghost Map coverThe Ghost Map: The Story of London's Most Terrifying Epidemic—and How It Changed Science, Cities, and the Modern World, by Steven Johnson (Riverhead Hardcover, October, 2006)

In 1854, two men—Dr. John Snow and the clergyman Henry Whitehead—unraveled the mystery of cholera, one of the 19th century’s most feared diseases. Steven Johnson’s The Ghost Map presents their work as an engrossing medical detective story, with impressive command of the historical material and magazine-style prose. The book is quite enjoyable, if somewhat pompous at times. The pacing is strong, and manages to keep the reader interested throughout. At about 250 pages, the book can be easily and profitably read in a weekend.

Today, the connection between microbes and disease seems self-evident. But for most of the 19th century, urban diseases occupied the mental space now reserved for shadowy terrorist networks—lethal, invisible, and unpredictable. Ironically, the bacteria that cause cholera, Vibrio cholerae, are asymptomatic or mild in most human infections, though they are still transmissible. They spread through the ingestion of food or water contaminated with human waste.  About 1 in 20 cases display the severe diarrhea that is the disease’s classic symptom.

Fluid loss in these cases can lead to extreme dehydration and death within hours, though cholera can be easily treated through rehydration therapy. At its most severe, the untreated disease can produce fatality rates of 50 percent or higher. In the 19th century, physicians understood neither how the disease spread nor how it killed.

By 1854, Snow had reached the pinnacle of the medical profession, but had lost none of his drive to expand the boundaries of medical science.

What physicians did have, however, was the “miasma” theory of disease. Dating back to the Greeks, the theory held that illness resulted from an imbalance in the four internal “humours” (fluids) of the body, and that these fluids could be affected by atmospheric disturbances—storms, humidity, even bad smells. 

When cholera made the jump from its natural home in India to Europe in 1817, and to England in 1832, miasma was blamed. The deadly ailment was assumed to be the result of the filth, smells, and “unclean living” that afflicted industrial London’s working class.

Snow was the right man in the right place at the right time to puncture the miasma myth. He had risen from humble beginnings to become one of London’s medical elite, in part by standardizing the dosage and delivery of new anesthetics like ether and chloroform. In 1853, no less than Queen Victoria asked for Snow to administer chloroform during the birth of her eighth child. By 1854, he had reached the pinnacle of the medical profession, but had lost none of his drive to expand the boundaries of medical science.

While it’s unclear what brought Snow’s powerful mind to bear on cholera, he quickly became dissatisfied with the miasma theory. If cholera spread through the air, like a gas, why did it strike randomly, even among those who shared the same environment? During his investigation of a severe outbreak in London in 1848-49, Snow thought he had the answer: the disease followed London’s water-supply routes. Snow published his theory, but it was greeted by polite skepticism. The London Medical Gazette challenged Snow to test his theory decisively:

The experimentum crucis would be, that the water conveyed to a distant locality, where cholera had been hitherto unknown, produced the disease in all who used it, while those who did not use it, escaped.

When, in 1854, a new cholera outbreak struck the London working class neighborhood of Soho, Snow found within walking distance of his office the test case he needed to prove his theory.

As the epidemic raged, Snow walked through Soho and, Johnson says, “drew lines of connection between individual pathology and the wider neighborhood…shifted perspective seamlessly from doctor to sociologist to statistician. He drew maps in his head, looking for patterns, looking for clues.”

The pattern Snow found led cholera back to its contaminated source, a water pump on Broad Street in Soho. Later, at an emergency meeting of the Board of Governors of St. James Parish, Snow persuaded the authorities to remove the pump’s handle—a “historical turning point,” Johnson rightly observes, since “for the first time a public institution had made an informed intervention into a cholera outbreak based on a scientifically sound theory of the disease.”

When, in 1854, a new cholera outbreak struck the London working class neighborhood of Soho, Snow found within walking distance of his office the test case he needed to prove his theory.

But Snow still couldn’t demonstrate how cholera had first infected the pump. For that task, he needed the assistance of someone even more familiar with the neighborhood than he was. Reverend Henry Whitehead’s parishioners were decimated by the Broad Street epidemic, and he later served on the St. James Parish committee investigating it. Initially, unconvinced by Snow’s theory, he set out to debunk it. Instead, he helped make it ironclad. 

Whitehead’s intimate knowledge of the area and his friendship with its residents helped him trace the epidemic back to its “index case,” its patient zero: an infant girl who had fallen ill in a house near the Broad Street pump just days before the epidemic exploded. Her mother had washed the child’s diapers in warm water and then discarded the water into a cesspool in front of the house that leaked directly into the Broad Street well.

Working from Whitehead’s findings and other data, Snow created a “Ghost Map” in 1855 that tracked the precise course of the Broad Street epidemic using “true street level knowledge.” In years to come, Snow’s map would become a textbook example of epidemiological research. 

Today, computer technologies allow epidemiologists to rapidly model, map, and track disease outbreaks on a global scale. Together with new advances in medicine and genetics, the invisible war between man and microbe is slowly but decisively shifting in mankind’s favor.

The Ghost Map also chronicles a subtle shift in modern society and politics. Alexis de Tocqueville, writing in the 1840s, praised America’s federal institutions for distributing decision making down to the local level, creating a more engaged and responsible citizenry. For most of the 20th century, however, power seemed to flow in the opposite direction, away from local institutions and toward unelected experts and bureaucrats who sought to remake urban landscapes according to their own utopian plans.

Top-down urbanism eroded urban civic culture precisely because local knowledge was excluded from the governing process; as a result, a real miasma—this time of crime, poverty, and urban blight—settled on America’s cities and has taken decades to unravel.

America’s recent urban renaissance was accomplished by policymakers who championed the importance of local knowledge. They valued the perspectives of ordinary people who live and work in neighborhoods and cities. The emergence of the Internet and an increase in networking will accelerate this trend, and herald a world where ordinary citizens have a growing voice in the media and public policy.  

“Increase the knowledge that the government has of its constituents’ problems, and increase the constituents’ knowledge of the solutions offered for those problems, and you have a recipe for civic health that goes far beyond the superficial appeal of ‘quality of life’ campaigns,” Johnson concludes. In our emerging networked world, flatter and smaller than ever, the street-level view of the amateur has become indispensable for the truly informed expert.

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