One-hundred-fifty year old lessons of John Snow still relevant today

08/27/04

Michigan State profs write comprehensive biography of British medical legend John Snow

EAST LANSING, Mich. It was 150 years ago this September that a London physician named John Snow urged officials in his city to shut down a well-used water pump in the heart of the Soho district, a move that may have helped to hasten the end of a deadly cholera epidemic that had killed hundreds of people.

What Snow correctly suspected was that the water coming from that pump was carrying particles or what he called "special animal poisons" that caused the disease, an idea scoffed at by most of the medical community of that time, most of which believed that diseases were spread primarily through the air.

It was that type of thinking that has made Snow one of the most revered figures in the history of medicine, and what prompted five Michigan State University professors who call themselves the "snowflakes" to spend six years writing a comprehensive biography on the life and times of John Snow.

Titled "Cholera, Chloroform, and the Science of Medicine: A Life of John Snow," the recently published book is what the authors call a "scientific biography" of the man who was a pioneering figure in the fields of epidemiology, anesthesiology, and medical geography.

"We came together because of his legacy," said co-author Michael Rip, an assistant professor in MSU's James Madison College.

"He brilliantly integrated insights from different types of scientific thought, from molecular to population, and he marshaled all scientific tools available to him, often with great ingenuity," wrote co-author Nigel Paneth, a professor of epidemiology who has written a piece about Snow that will appear in the September issue of the journal Epidemiology.

Howard Brody, a professor of family practice and a co-author, said in doing research for the book he was constantly amazed at Snow's ability to think beyond what was already known.

"It was as if I was reading something written by a contemporary, very direct and logical and to the point," he said. "Somehow Snow managed to be both of his time and ahead of his time."

Perhaps Snow's greatest contribution to medicine was his hypothesis that cholera and other diseases could be spread by means other than the air. In the mid-19th century, it was believed that if a disease-causing agent found its way into water, it would soon become diluted and essentially harmless.

Even more amazing, said Stephen Rachman, associate professor of English and co-author, was that Snow formed his conclusions nearly 30 years before Louis Pasteur work with germ theory.

"It's interesting to note that Snow came to his conclusions before germ theory and that he didn't even use that concept," he said. "Indeed, he called the agents that caused diseases like cholera 'special animal poisons.' To me, that makes his work all the more impressive."

Although Snow knew his way around a laboratory, in this case it almost didn't matter.

"Snow said even if we can't identify whatever this thing is that causes cholera, we have enough information at our disposal to prevent further spreading of the disease," said Peter Vinten-Johansen, a history professor who served as lead author. "The circumstances are such that we can undertake a reasonable set of public health precautions that are going to be effective."

These epidemiologic lessons remain true today, said Paneth, who founded MSU's Department of Epidemiology. He said it's not uncommon to first discover the way in which a disease is transmitted, act on that, and then do the lab work necessary to totally wipe it out.

"Once the mode of communication of a disease is established, preventive measures nearly always follow, a principle as true for SARS in the 21st century, as it was for AIDS in the 20th century and cholera in the 19th," he said.

Rachman said Snow realized that disease-causing agents didn't distinguish between the rich and poor. Many at that time believed cholera was a disease that only attacked the poor.

"He practiced on a diverse population, from the poor and indigent to the well-to-do," Rachman said. "His sense of cholera as a waterborne agent that could strike anyone was very modern in a time when most people and physicians tended to make distinctions along class lines."

Most of the book focuses on the later years of Snow's short life he died in 1858 at the age of 45 partly because very little is known of his early days. However, said Vinten-Johansen, the book does give a good feel for the times.

"We were able to find the diary of someone who was apprenticed around the same time just down the street from where Snow practiced," he said. "We also found the diary of a London medical student from that time too."

In addition to capturing many of Snow's accomplishments, the book also serves to bust a few myths about him.

It had long been thought that Snow himself removed the handle that would shut down the Broad Street pump, thus single-handedly ending the epidemic (he didn't). It was also reported that Snow had taken a map of the cholera-infected area, marked the houses in which cholera deaths had occurred, and in that way figured out that the water from the Broad Street pump was the culprit.

While he was able to pinpoint the Broad Street pump as the source of the epidemic, he did it by much simpler means. He interviewed survivors and relatives of those who had died from cholera. Those who were sick or died got their water from that particular pump.

"The map was used merely to illustrate that many cases were nearer to the Broad Street pump than to other pumps," Paneth said. "But he had concluded that the pump was the problem well before he drew the map."

The book was published by Oxford University Press.

Source: Eurekalert & others

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