John Snow Pub, London Snow’s second investigation reexamined buy minocycline no prescription  data from the 1854 cholera outbreak in London.

During a cholera epidemic a few years earlier, Snow had noted that districts with the highest death rates Pharmacorp 24 minocycline  were serviced by two water companies: the Lambeth Company and the Southwark and Vauxhall Company.

At that time, both companies obtained water from the Thames River at intake points that were downstream from London and thus susceptible to buy minocycline online  contamination from London sewage, which was discharged directly into the Thames.

To avoid contamination by London sewage, in 1852 the Lambeth Company moved its intake water works to a site on the Thames well upstream from London.

Over a 7week period during the summer of 1854, Snow compared cholera mortality among districts  that received water from one or the other or both water companies.

1 Mortality from Cholera in the Districts of London Supplied by the Southwark and Vauxhall and the Lambeth Companies, July 9August 26, 1854 — —1r1 Districts with Water Supplied By:Population (1851 Census)Number of Deaths from CholeraCholera Death Rate per 1,000 Population Southwark and Vauxhall

1 show that the cholera death rate was more than 5 times higher in districts served only by the Southwark and Vauxhall Company (intake downstream from London) than in those served only by the Lambeth Company (intake upstream from London).

Interestingly, the mortality rate in districts supplied by both companies fell between the rates for districts served exclusively by either company.

These data were consistent with the hypothesis that water obtained from the Thames below London was a source of cholera.

Alternatively, the populations supplied by the two companies may have differed on other factors that affected their risk of cholera.

To test his water supply hypothesis, Snow focused on the districts served by both companies, because the households within a district were generally comparable except for the water supply company.

In these districts, Snow identified the water supply company for every house in which a death from cholera had occurred during the 7week period.

2 Mortality from Cholera in London Related to the Water Supply of Individual Houses in Districts Served by Both the Southwark and Vauxhall Company and the Lambeth Company, July 9August 26, 1854 Water Supply ofPopulationNumber of DeathsCholera Death Rate per Individual House(1851 Census)from Cholera1,000 Population Southwark and

This study, demonstrating a higher death rate from cholera among households served by the Southwark and Vauxhall Company in the mixed districts, added support to Snow’s hypothesis.

It also established the sequence of steps used by currentday epidemiologists to investigate outbreaks of disease.

Based on a characterization of the cases and population at risk by time, place, and person, Snow developed a testable hypothesis.

He then tested his hypothesis with a more rigorously designed study, ensuring that the groups to be compared were comparable.

After this study, efforts to control the epidemic were directed at changing the location of the water intake of the Southwark and Vauxhall Page 110 Company to avoid sources of contamination.

Thus, with no knowledge of the existence of microorganisms, Snow demonstrated through epidemiologic studies that water could serve as a vehicle for transmitting cholera and that epidemiologic information could be used to direct prompt and appropriate public health action.

19h and 2(fh centuries In the mid and late1800s, epidemiological methods began to be applied in the investigation of disease occurrence.

At that time, most investigators focused on acute infectious diseases.

In the 1930s and 1940s, epidemiologists extended their methods to noninfectious diseases.

The period since World War II has seen an explosion in the development of research methods and the theoretical underpinnings of epidemiology.

Epidemiology has been applied to the entire range of healthrelated outcomes, behaviors, and even knowledge and attitudes.

The studies by Doll and Hill linking lung cancer to smoking6and the study of cardiovascular disease among residents of Framingham, Massachusetts7 are two examples of how pioneering researchers have applied epidemiologic methods to chronic disease since World War II.

During the 1960s and early 1970s health workers applied epidemiologic methods to eradicate naturally  occurring smallpox worldwide.

This was an achievement in applied epidemiology of unprecedented proportions.

In the 1980s, epidemiology was extended to the studies of injuries and violence.