It’s 1854 in London. The third major cholera pandemic was racing through the city. Spreading from the Ganges delta of India since 1837, it’s claimed over a million lives mostly among Asia, Europe, and North America.
Within the Soho district of Westminster, London, things weren’t looking good. The London sewer system had not reached Soho, but a large influx of people had. Animal droppings from cowsheds and slaughter houses lined the streets. Many cellars had cesspools underneath, formed from the sewage and filth seeping in from outside. Making matters worse, the London government was dumping waste into the River Thames and contaminating the water supply.
At the time, people generally thought that a noxious form of bad air called “miasma” (Greek for “pollution”) was at the heart of disease and the origin of epidemics. The thought was that decaying organic matter released miasmatic particles into the air.
One physician, John Snow, who is now known as the father of modern epidemiology, was skeptical of the miasma theory of disease. Snow thought that germ cells (unidentified at the time) was transmitted during ingestion of contaminated water and caused the illness. (Louis Pasteur did not propose germ theory until 1861.)
In August of 1854, 127 people living on or near Broad Street in Soho died in 3 days. A week later, 500 people were dead. After interviewing with the family of cholera victims, Snow found that nearly every case was clustered around a water pump at the corner of Broad and Cambridge streets.This water pump was supplied from the River Thames. Other pumps received water from another source other than the Thames and there were fewer deaths in those neighborhoods.
He collected water from the pump and saw “white, flocculent particles” in the water. This convinced him that the water source was the culprit behind the disease. Yet the microbe, Vibrio cholerae was not isolated until later that year by the Italian anatomist Filippo Pacini.
At the time, experts were doubtful of Snow’s findings and conclusions, siding with the favored miasma theory of disease. And while London authorities were skeptical, Snow convinced them to remove the handle from the pump to lock access. The outbreak ended.
Later, Snow used a dot map to plot the cluster of cholera cases and pump locations in Soho. Snow was able to connect the cholera cases with the pump and the water company that supplied water from the Thames.
(One exception: the Broad Street brewery near the pump. None of the workers contracted cholera as they were given an allowance of beer and did not consume the water.)
John Snow’s discovery and role in ending the Broad Street outbreak has many points of significance. It demonstrates shifting views from miasma theory of disease to the germ theory of disease and it’s considered the founding event of modern epidemiology.
