John Snow: A Legacy of Disease Detectives

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Snow cholera map
Map of cholera cases in Soho, London, 1854. Source: Wikimedia Commons.

John Snow, known as the father of epidemiology, was born on March 15, 1813. This week, we honor the birthday of the first true disease detective.

The Story of the Broad Street Pump

London, 1854: A cramped Soho neighborhood teems with people and animals living in cramped and dirty quarters. A deadly outbreak of cholera is spreading. Doctors and scientists believe it’s caused by “miasma,” or bad air. They theorize that particles from rotting matter and waste are getting into the air and making people sick.

Enter John Snow. An accomplished physician, he becomes convinced that something other than the air might be responsible for the illness. Through carefully mapping the outbreak, he finds that everyone affected has a single connection in common: they have all retrieved water from the local Broad Street pump.

On September 8, 1854, Snow tests his theory by removing the pump’s handle, effectively stopping the outbreak, proving his theory, and opening the door to modern epidemiology.

Valuable Lessons for a Modern Age

In 1854, John Snow was the first to use maps and records to track the spread of a disease back to its source. Today, his ideas provide the foundation for how we find and stop disease all over the world.

We have better, more modern tools now for identifying and tracking illness, like access to state-of-the-art labs and computer systems. We have in-depth knowledge of germs and how they spread. But when we train today’s disease detectives, we still return to the basics. CDC disease detectives are trained to look for clues by asking:

  • WHO is sick?
  • WHAT are their symptoms?
  • WHEN did they get sick?
  • WHERE could they have been exposed to the cause of the illness?

We live in a world where disease can travel across the globe in a matter of hours. This means we must not only apply these basic lessons of epidemiology, but we must constantly be looking for ways to find better answers, faster.

Disease Detectives Make a DifferenceEpidemic Intelligence Service

When outbreaks or other threats emerge, CDC’s disease detectives, some of whom are trained through our Epidemic Intelligence Service (EIS), are on the scene. These boots-on-the ground staff, called EIS officers, support over 100 public health investigations (Epi-Aids) each year in the U.S. and worldwide.

CDC’s disease detectives have been instrumental in tracking down threats like:

Anthrax: During the 2001 anthrax outbreak among U.S. postal workers, disease detectives investigated the route of contaminated envelopes and how workers became infected.

E. coli: For the first time, disease detectives conclusively showed that flour was the source of a 2016 E. coli outbreak. Millions of pounds of flour were taken off the shelves, including flour-containing products like bread, cake, and muffin mixes.

Seoul virus: Disease detectives have been working to track and stop an outbreak of Seoul virus, an emerging rodent-borne hantavirus, involving home-based rat breeders this year. The outbreak was first identified after two Wisconsin rat breeders became ill in December and, as of March 13, the investigation has so far included rat-breeding facilities in 15 states, with 17 people infected in seven states.

Like Snow’s map that revealed cases of cholera congregated around the Broad Street pump, we must keep tabs on where and how disease is spreading. Once the source of disease is identified, it is crucial to develop and implement interventions to help prevent people from getting sick. We must remain innovative and creative, like Snow when he removed the handle of the Broad Street pump to stop disease at the source.


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7 comments on “John Snow: A Legacy of Disease Detectives”

Comments listed below are posted by individuals not associated with CDC, unless otherwise stated. These comments do not represent the official views of CDC, and CDC does not guarantee that any information posted by individuals on this site is correct, and disclaims any liability for any loss or damage resulting from reliance on any such information. Read more about our comment policy ».

    As a public health officer JS’s method is still valid in low income countries.However, technology has gone milestones but can not do without JS’s expertise.
    Now on a separate note l am interested to embark on an EIS course. ANY ADVISE PLEADE

    As a public health officer JS’s method is still valid in low income countries.However, technology has gone milestones but can not do without JS’s expertise.
    Now on a separate note l am interested to embark on an EIS course. ANY ADVISE PLEASE

    Also didn’t John Snow discover that in one neighborhood of Soho the people did not have the same outbreak because they drank more beer and less water. The brewery was in that same neighborhood.

    Not trying to be funny here, I believe this is a fact? Please correct me if I am wrong. This came to me from an MBA study on epidemiology many years ago.

    Eventually we know that JS’s method are used long time ago and we have advanced techniques of diseases detection but still the origin of the methods still valid as it was invented by JS’s !!! I am a field epidemiologist who greatly inspired with his contributions for public health and I believe no scientific knowledge will be evident today if he is not been there some 200+ years ago !

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Page last reviewed: March 14, 2017
Page last updated: March 14, 2017