The Epidemiological Transition
Citation: United, Nations The Epidemiological Transition.
This descriptive account of the epidemiological transition begins by asserting that the process of mortality change from infectious to chronic diseases is well underway in every part of the world. In developed countries, about 90 percent of deaths are now due to non-communicable diseases. Although communicable diseases play a much larger role in developing nations, particularly in sub-Saharan Africa and India, they are generally becoming less important as the epidemiological transition proceeds. For instance, in China 73 percent of all deaths are due to non-communicable diseases; in Latin America, 56 percent.
Data for this report are taken from (1) the WHO's most recent estimates (1997) of deaths by cause for both developed and developing regions, and (2) the Global Burden of Disease Study (GBD)-a 5 year project initiated in 1992. A fundamental aim of the GBD was to derive estimates of mortality for 107 causes of death by age, sex and region. Some nations, primarily those with established market economies, have sophisticated vital registration systems that made this task relatively easy and accurate. But others, particularly those in sub-Saharan Africa, have no such information. Most nations fall somewhere between these extremes. For instance, sample registration systems exist in both India and China. Where gaps exist in vital registration systems, data were taken from samples, data from population laboratories (e.g., Matlab), epidemiological studies and cause of death models.
As the epidemiological transition has proceeded, life expectancy for the entire world has improved from 46.5 in 1950 to 64.3 in 1990. Gains in life expectancy have been especially impressive in developing nations, and the gap between developed and less developed regions fell from about 25.6 to 12.1 years. However, this overall improvement in developing regions masks important variation between poor nations. For instance, despite progress, child mortality remains high in some developing nations (e.g., 254 per 1,000 in Guinea) relative to others (e.g., 59 per 1,000 in Botswana). Generally speaking, India and sub-Saharan Africa still suffer from relatively high rates of infectious disease and childhood mortality, while China and nations in Latin America are leaders among developing nations in the epidemiological transition.
In addition to reductions in mortality, fertility rates have been declining for both developing and developed nations. This alters the age structure of the population from relatively young to relatively old, and therefore increases the burden of non-communicable disease mortality. "By the early 1990s, non-communicable diseases were responsible for close to 60 percent of deaths worldwide" (p. 105). Future gains in life expectancy-particularly in developed nations-depend on trends in chronic disease mortality at older ages. The report cautions against overconfidence in forecasting, but also suggests that declines in old age mortality are likely to continue.
Even where the epidemiological transition has made great progress, it is important to recognize that chronic disease profiles can vary greatly between nations/regions. For example, mortality from cerebrovascular diseases (especially stroke) is far more common in Asian nations than in North America or Europe, where cardiovascular disease is highly prevalent. These differences are likely due to different risk factor profiles among countries. Moreover, within nations, "the epidemiological transition appears to have occurred along socio-economic lines, with a growing prevalence of chronic and degenerative diseases of adulthood among the better off, while communicable diseases remain relatively more prevalent among the poor" (p. 107).