John Snow: Cholera

John Snow's approach to explaining cholera and how it spread consisted primarily of morbid poison entering the alimentary canal through means of contaminated water consumption. Snow believed this to be the basis of how cholera was contracted by individuals and believed improper sewage filtration was to blame as well as a means of spreading the disease from person to person. However, previous explanations of how cholera was contracted consisted of the theory of airborne infection. This theory proposed that cholera was contracted by inhaling air at low levels of altitude by such people as workers in slaughterhouses and bone merchants. This theory also proposed that the foul-smelling odors associated with these occupations were closely correlated with transmission. Having had previous knowledge of respiratory physiology, Snow dismissed the idea of cholera spreading by means of airborne infection because it had no relevance of what he already knew of inhalant anesthetics. Snow backed up his position by pointing out that if inhaling air in a workplace such as a slaughterhouse were the means in which the transmission of cholera occurred, then the workers in them would be primary targets in contracting the disease. Since this was not the case, Snow continued to stick with his theory of cholera being transmitted by swallowing "morbid matter" specific to the disease. (Snow)

Snow further attempted to prove his theory of waterborne transmission of cholera by conducting studies in various London sub districts in August of 1848. In this study he found that homes whose water was supplied to them by the Lambeth Water Company had few incidents of cholera, whereas homes whose water was supplied to them by the Southwark and Vauxhall Water Company had high incidences of cholera. Snow concluded that the reasons for various cholera incidents involving different water companies had to do with where the companies drew their water supply. Snow believed Lambeth Water Company customers had few incidents with cholera because their water came from the upper reaches of the Thames River ("water free from heavy fecal contamination of the lower reaches of the Thames"), whereas Southwark and Vauxhall Water Company had high incidences of cholera because their water came from the lower reaches of the Thames River (water with heavy fecal contamination). (Snow) Although this study shows strong correlation involving contaminated fecal water and cholera, people were still hesitant in believing Snow's theory of cholera victims becoming infected by swallowing other people's fecal matter. Thus, most people continued to support the airborne infection theory.

In what would later in time be acknowledged by society as strong convincing evidence in support of Snow's theory of cholera; Snow yet again conducted a study in which he correlated mortality with the source of water. This time his study was far less vague than his previous study and accurately linked the outbreak of cholera in Golden Square to the water pump on Broad Street. Snow went about conducting his study by interviewing all the residents of Broad Street; the majority of which complained of smelling an unpleasant odor coming from the water pump on Broad Street. Based on interview complaints alone, Snow then sought out statistics concerning cholera deaths in the Soho area. The results Snow found correlated strongly with his initial belief of how cholera was spread. These results indicated that the majority of cholera deaths occurred in the vicinity of the Broad Street water pump. Although Snow's findings initially provoked the board of governors of the local St. James Parish to remove the Broad Street pump handle, the medical board of London were not entirely convinced and ordered the pump handle to be replaced.

Although Snow was never able to convince his peers early on of his theory that ingestion of contaminated water was the cause of cholera, he did recommend actions that could be taken in the presence of cholera and for preventing the disease from spreading. These actions Snow provides in his pamphlet, "On the Mode of Communication of Cholera" consists of twelve measures society can perform in the presence of cholera and in preventing cholera and other diseases that are communicable in the same manner from spreading. The basis of the measures Snow suggests are strict cleanliness when dealing with sick individuals, proper preparations and filtration of water, and isolation between individuals that are sick and those who are not. Snow's measure of strict cleanliness consisted of people exhibiting proper hygiene skills when dealing with disease stricken individuals by means of correct hand washing techniques, proper disposal of infected garments, and appropriate means of food handling. Snow was also an advocate