John Snow Father Epidemiology Pioneering Research Analogy

¶ … John Snow father epidemiology pioneering research analogy containment cholera outbreak London 1800's. However, contributor, William Farr, provided substantial information data understanding etiology spread cholera research surveillance

John Snow is known as the founder of modern epidemiology. Summarize his works and findings, describing the premise on which his experiments were formulated. How did Snow explain that cholera's first symptoms were abdominal pains? How does his work demonstrate the scientific method?

Snow first examined the symptoms of cholera to trace the disease's likely epidemiological history. Because the first symptoms were abdominal pain and relieved by palliatives like opium, chalk or catechu, this seemed to indicate that cholera was caused by an ingested substance, like water. The first step of the scientific method is to form a hypothesis, based on research. Snow researched the transmission and spread of other contagious illnesses transmitted person-to-person like smallpox, cowpox and syphilis, and based his hypothesis about the likely cause of the epidemic on the initial location of the disease in the body in the area of the digestive tract (Eyler 2001:225).

Once he arrived upon his hypothesis, Snow attempted to prove it through empirical investigation and observation. First, he had to establish that it was possible to transmit the disease from a contaminated water supply to the digestive tract. He noted that a pump's water supply had been contaminated by washing the diapers of a child infected with cholera, and two people who drank from the pump who did not live in the area came down with the illness (Eyler 2001:225). This suggested that the illness was transmitted through ingestion, not through other means, such as inhalation.

While the Broad Street pump incident provided anecdotal evidence for the Snow hypothesis, broader epidemiological evidence was required. This was provided by a comparison of populations served by two water companies, that of the Southwark and Vauxhall vs. The Lambeth Waterworks corporations. Rates of cholera mortality were fourteen times higher in the population that drank from the less pure water source, that of the Southwark and Vauxhall supply (Eyler 2001:226). In contrast, the Lambeth Company received their water supply from an area free of the sewage of London (Morabia 2001: 223).However, because Snow's study did not have strict controls (many individuals drank from both water supplies, for example) it was far from conclusive and met with derision in some quarters (Eyler 2001:227).

Q2. What occupational position did William Farr hold? What significant information did Farr compile in relation to the cholera outbreaks? What were the factors he thought contributed to the spread and mortality of cholera? What was the vector (mode of transmission) that Farr attributed to the person-person spread of cholera?

Farr was the Statistical Superintendent of the General Register Office and had access to a massive amount of statistical and demographic data. Farr was more impressed by the geographical concentration of the epidemic than Snow, as costal districts had three times higher the mortality rate of inland districts. Farr believed that elevation could predict the likelihood of contracting cholera and attributed its spread to what he called the 'zymotic' material of cholerine. In Farr's experience, disease was most likely to spread in the close quarters of slum districts, prisons, and other areas where there was a considerable amount of cross-contamination of the same bad air. Demographically, the highest rates of mortality were consistent with districts of the lowest elevation, which Farr surmised had the worst air quality (Eyler 2001:228-229). Farr believed that sewage contained 'miasma' that transmitted disease but was not specifically the main carrier of the illness.

Q3. Briefly comment on the impact of Farr's work on Snow's and vice versa

Farr was intensely interested in Snow's work, and did note, during the epidemic of 1853 the change in water supply of the Lambeth Company. However, he believed initially that Snow's findings supported his original hypothesis, as contaminated water was supposed to be a transmitter of miasmic material that could enter the body through inhalation. Despite Farr's initial rejection of Snow's correct hypothesis, the more detailed and methodological approach of Farr was more persuasive to scientists of the day. Yet by the time of the next cholera outbreak in 1866, Farr had become converted to Snow's theory. Farr decided that the origins of the epidemic were linked to the fact that the East London Waterworks Company had changed the source of its supply to a much more contaminated area (Eyler 2001:230).

This provided the kind of large controlled study that Snow's initial hypothesis lacked to substantiate itself. Farr also had the ability to reference the data he had accessed as part of his profession to substantiate Snow's hypothesis that contaminated water was the primary method of transmission. However, he still clung to the belief that in some exceptional cases sewage vapor might cause cholera (Eyler 2001:230).