The term epidemiological transition refers to the shift in cause-of-death patterns that comes with the over-all decline of death rates. In European countries the fall in death rates, which began after the middle of the eighteenth century, came about because of a decline in infectious disease mortality (chiefly from cholera and tuberculosis). The victory over infectious diseases allowed people to live longer and hence to develop the chronic degenerative diseases that became the main causes of death during the twentieth century: heart disease, cardiovascular disease, and malignant tumors.

Idea comes from: Omran's Age of Pestilence and Famine

These stages go along with the demographic transition

Stages 1 and 2

Stage 1: "The Age of Pestilence and Famine when mortality is high and fluctuating, thus precluding sustained population growth" (Omran). Average life expectancy at birth is low and variable, in the range of 20 to 40 years.

The Black Plague was the most violent of the epidemics of stage one
http://en.wikipedia.org/wiki/Black_Death(external link)

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Stage 2: "The Age of Receding Pandemics when mortality declines progressively and the rate of decline accelerates as epidemic peaks become less frequent or disappear. The average life expectancy at birth increases steadily from about 30 to 50 years. Population growth is sustained and begins to describe an exponential curve" (Omran).

There are, however, still problems with pandemics (diseases that occur over a wide area). Many of these center in the industrial cities now being created that crowd people together.

Example:
John Snow and the cholera epidemic of London
http://en.wikipedia.org/wiki/1854_Broad_Street_cholera_outbreak(external link)

Video on John Snow and the epidemic
http://www.ted.com/talks/lang/eng/steven_johnson_tours_the_ghost_map.html(external link)

Stages 3 and 4
The stage after the transition, "The Age of Degenerative and Man-Made Diseases when mortality continues to decline and eventually approaches stability at a relatively low level. The average life expectancy at birth rises gradually until it exceeds 50 years. It is during that stage that fertility becomes the crucial factor in population growth" (Omran).

Stage 3
Major health issues
-heart attacks and cancer
-decline in infectious diseases thanks to widespread use of vaccines (examples, polio, measles)


Stage 4
The stage of delayed degenerative diseases. Same causes of death as stage three but widespread use of the latest medical advances and surgical operations causes a delay of death and extends longevity.

Possible Stage 5
-resurgence of epidemic diseases caused by antibiotic resistant strains and new diseases that come from animals (SARS, Avian bird flu, etc)

Reasons
Evolution of diseases because they are resistant to drugs or disease carrying insects that are now resistant to pesticides like DDT (mosquitoes resistant to DDT carry malaria)

Poverty- Long expensive treatments make TB an issue in LDCs but not MDCs. AIDs could be argued to be another example of this.

Improved Travel- Pandemics (diseases over a wide area) are now more likely because we travel so much more. H1N1, SARS and AIDs all traveled a great distance in a very short period of time.



http://www.novelguide.com/a/discover/epop_01/epop_01_00112.html(external link)