John Snow, Cholera Outbreak, 1854

John Snow.  Snow on cholera : being a reprint of two papers. Rare and Distinctive Collections, CU Boulder Libraries.

Doctor John Snow conducted his epidemiological work during the mid-1800s. Trying to better understand the transmission dynamics, he produced maps regarding the cholera outbreak in London, 1854. The map included here, centered around Broad Street where the disease affected the most people, was arguably his most popular work. Within this map, Snow primarily visualized two different variables: cholera decedents and water pump stations. Information regarding building location and roads were also included. Inside of each building, Snow marked the number of cholera-related deaths, in an attempt to show the clustering around the Broad Street water pump. Since Snow decided to look at these variables from a spatial perspective, he could better determine some sort of relationship. However, he fell short in the supplemental evidence needed to prove his theory and therefore his work was largely considered speculative.

The work of Dr. John Snow is highly regarded now in the fields of epidemiology and public health. Falling short just a few years earlier, Snow was eager to prove his theory that cholera was a waterborne disease and therefore could be traced. Specifically, he “suspected contamination of the water pump in Broad Street” (Snow, 2004) to be the source of spreading cholera in the Soho neighborhood. The maps he created were an effort to support his claim and help to show the spatially explicit nature of the outbreak. Yet, the evidence used doesn’t hold much more depth than this and Snow “believed his argument so utterly convincing he did not need to consider carefully the alternate theories others put forward in separate studies” (Koch, 2009, 1250) and therefore undermined any sort of validity for his work. It was through this disregard of a proven methodology that he lost credibility. Thus, Snow’s idea was easy to challenge and during the epidemic, many people chose to uphold the longstanding theory of miasma – “bad air” – rather than exploring Snow’s work. These people believed that “bad air” originating from “a 1665 plague burial site on which housing had been built and under which new sewers had been laid might be a source of [the] cholera contagion” (Koch, 2009, 1247). Additionally, others also believed that the bad odors were created and carried by the sewer themselves. While Snow was quick to dismiss these alternative views, another critique he received was that no other analysis was completed on other water pump areas around the city. He fell short in the methods chosen to conduct his study. It seemed that, given the evidence he presented, “[not] any one can feel that even a tolerable case is made out in favour of Dr. Snow's opinion” (Parkes, 1855).

Despite being highly opposed, other works still corroborated Snow’s ideas and highlighted the importance of his work to the contribution of a better understanding of not only cholera, but the entirety of disease transmissions. Koch and Denike, in their 2009 journal article, explored the criticisms using a variety of statistical and spatial methods. Their findings validated “how much greater the risk for the Broad Street pump service population was compared to the remainder of the population” (Koch, 2009, 1250). During and shortly after the height of the epidemic, Snow’s work was explored by Henry Whitehead as well. Being a local church leader, Whitehead knew this community and, in 1855, he helped to publish a report that acted partially as a testimonial to the work Dr. Snow completed during the cholera outbreak of 1854. Whitehead, embracing the credibility he held within the community, confirmed that in “Dr. Snow’s report, the number of daily attacks is also fully and carefully reckoned” (Cholera Inquiry Committee, 1855, 23). Whitehead was able to recognize the importance of the map Snow created and found it valuable to share his results.

While Snow’s critics did hold validity in their concern for his work, the accuracy of Snow’s findings are evident now. His map correctly identified the spatial relationship between cholera-related deaths and water supplies, all while creating an easily digestible visualization of the outbreak. The work of Dr. John Snow and this one map in particular, serve as a foundation for the fields of Epidemiology and Geographic Information Science (GIS).