Snow viewed the second death as strong evidence of contagion. He suspected that the room had not been cleaned after Harnold's occupancy and that perhaps some cholera germs had remained in the bed linen.
As more cases appeared, Snow began examining sick patients. All of them reported that their first symptoms had been digestive problems. Snow reasoned that this proved that the disease must be ingested with polluted food or water. If the victims had absorbed cholera poison from polluted air, as the "miasma" theorists believed, then their first symptoms should have appeared in their noses or lungs -- not in their digestive tracts. Snow theorized that the extreme diarrhea that characterized the disease might be the mechanism that spread the germs from one victim to another.
Perhaps the fatal germs were lurking in the great volumes of colorless fluid that patients expelled. If just a few drops of that fluid contaminated a public water supply, the disease germs could be spread to countless new victims.
Snow discussed his theory with colleagues. He searched through medical journals and government reports about cholera looking for references to water conditions and sewer facilities, and he sent written queries about water conditions and sewer facilities to authorities in areas with high mortality from the disease.
In August of , during the second year of the epidemic, Snow felt obliged to share what he considered convincing evidence that cholera was being spread through contaminated water. At his own expense he published a pamphlet entitled On the Mode of Communication of Cholera. Thirty-nine pages in length, the essay contained both a reasoned argument and documentary evidence to support his theory. As one example he cited the case of two rows of houses in a London neighborhood that faced each other.
Since the definition by the CDC is complex, a reader can explore individual terms by clicking on each word to see the CDC definition. Epidemiologist in Public Health performs numerous roles including collection and analysis. Background Epidemiology is the study of how often diseases spread through a population.
This information can be used to help reduce the damage caused in future epidemics and also help to understand the best way to treat patients of a current epidemic. However nowadays epidemiology is not limited to diseases among human populations, epidemiology can now be the study of disease in any defined population. But five star exhibits will be displayed in prominence for their impact shaped the course of science.
First is John Snow who revolutionized the way medicine was conducted. Secondly there is Isaac Newton, who is dubbed the father of the scientific revolution. Rachel Carson is the next prominent exhibit.
John Snow is considered the father of the modern epidemiology. Epidemiological studies are applied to the control of health problems in populations. The first cholera epidemic in London struck in , when Snow was still an apprentice. Another large epidemic occurred in and lasted through The prevailing opinion was that cholera was spread either by miasmas or by person-to-person contact, Snow began examining the victims and found that their initial symptoms were always related to the gastrointestinal tract.
Snow reasoned that, if cholera was spread by bad air, it should cause pulmonary symptoms, but since the symptoms were gastrointestinal, perhaps it was transmitted by water or food consumption.
In fact, cholera is caused by the bacterium, Vibrio cholera, which is transmitted by the fecal-oral route, that is by ingestion of water or food that is contaminated with sewage. In August Snow published a paper entitled " On the Mode of Communication of Cholera " in which he presented his theory that the disease was acquired by ingestion of contaminated water, but his theory did not get much traction with the medical establishment.
The epidemic ended in , but Snow continued to collect data on the pattern of of disease and began finding evidence that linked cholera to specific sources of water. Many Londoners received their water from hand pump wells below that were located throughout the city. However, increasing numbers of businesses and homes had water piped from the Thames River by private companies. Snow learned from municipal records that two private companies supplied piped in water to the areas that were primarily affected by cholera.
The map of London below shows the areas of London supplied by these two water companies. Nevertheless, many were unconvinced by his findings, since Snow had not actually demonstrated that the water contained something that could cause cholera.
In late August of , cholera broke out in the Broad Street area, and the residents panicked and many began to flee. A hand pump was located right on Broad Street, and Snow was immediately suspicious. Water samples did not reveal gross contamination, but Snow persisted and began to collect detailed information on where the victims had gotten their drinking water.
He obtained the names and the addresses of the first 83 victims who had died by the end of the first week. WHO also reports cholera outbreaks making news in various regions of the world, and often includes a map of the outbreak site.
Andrew Hayward presents the history of cholera, including John Snow's contributions, in a Supercourse lecture. Morris on what was learned in England following the first cholera epidemic of , to help prepare for London's epidemics of and Snow was also prominent as an anesthesiologist. He administered chloroform to the Queen on two occasions. The story, Death in Bristol , started in February , four months before Snow's death.
It was his last published exchange, but involving anesthesiology rather than epidemiology. This section tells what happened and the location of the water companies that provided the exposure. Tufte has thoughts on John Snow and his visual display of Broad Street cholera cases. The authors of a July 1, article in The Lancet believe the story is more involved, and certainly more fascinating. Cartographer Tom Koch adds fuel to the myth-making fire by showing how depictions of Snow's map of the Broad Street pump outbreak have been altered over time.
The author of this article in the Journal of Medical Biography presents an interesting account of Farr, often viewed as the "father" of modern vital and health statistics. Farr during his lifetime had more scientific supporters but Snow eventually reached greater fame, arising from being right. Historian John Eyler authors a thoughtful article on the changing assessment of these two scientists, then versus now.
A plaque describes his link to the region and the reasons for his fame. John Snow. Deadly River book website.
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