John Snow and the Beginning of Epidemiology

Those of us, who toil in obscurity, should take heart.  Good ideas are eventually acknowledged.  I’m working on the changes for the sixth edition of my book Health Economics and Policy and am discovering interesting facts almost daily. 

Public health as a modern-day science can trace its roots back to 19th century England and the pioneering work of young British surgeon, John Snow.  Responsible for advances in anesthetic surgery, Snow is best known for his work in epidemiology during London’s worst outbreaks of cholera between 1848 and 1854. 

The first cholera outbreak in Britain in the modern era occurred in 1831, killing over 23,000 inhabitants.  The government response was minimal, but the aftermath did see an increase public awareness on improving sanitary conditions of the poor and working class.  A white paper was ultimately published in 1842 providing momentum for the passage of the first public health bill in 1848, known unofficially as the Cholera Bill. 

A second cholera outbreak occurred in 1848, followed by another one year later, resulted in 250,000 cases and 53,000 deaths.  During these two outbreaks Snow observed particularly high death rates in the Soho area of London.  The commonly-held scientific belief of the day assumed that cholera was an airborne disease.  But Snow did not accept any of the many miasma, or bad air, theories of transmission.  He argued that because the symptoms were intestinal, it was likely that cholera was a waterborne disease and entered the body through the mouth. 

At the time of the second and third epidemics, there were two water companies serving the Soho district, Southwark and Vauxhall Waterworks and Lambeth Water Company. Both had their water intake source in the tidal basins of the Thames River, downstream from the major population areas.  Using basic spatial analysis to prove his hypothesis, Snow mapped the cholera deaths and identified patterns associated with the water sources available in the neighborhoods. 

In 1854 another cholera outbreak occurred, providing Snow with another opportunity to advance his theory.  This time, however, he was provided with a perfect natural experiment to test his hypothesis.  In 1852 Lambeth moved its water source upstream in an area of the Thames that was not affected by the tidal waters and was thus much less polluted.  Moving house to house, he spent several months mapping the occurrence of the disease and noted the difference in the death rates between the customers of the two water companies.  Lambeth customers had a death rate of 180 per 100,000 customers while the death rate for Southwark and Vauxhall customers was 916 per 100,000, over five times as high.  

Snow was able to convince the local water authorities to take the handle off the water pump on Broad Street (now Broadwick Street) that was the source of contaminated water for many of the local residents, and cholera cases diminished immediately.  He documented his research in a book entitled On the Mode of Transmission of Cholera in 1855.  But the cholera problem did not end there.  Unfortunately most of the scientific community continued to hold to the miasma theory of cholera transmission for several decades.  It was not until Koch and Pasteur developed the germ theory of disease long after Snow’s death that his theory of transmission was substantiated.