The epidemiological transition

Overview

Epidemiological transition and double burden of disease.

What you need to know

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Questions from this subtopic

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1. 1

   What is the epidemiological transition?

   Model answer

   It is the long-term shift in the dominant causes of death and illness in a population as it develops: away from infectious and parasitic diseases, malnutrition and famine, which kill mainly infants and young children, and towards chronic and degenerative diseases — heart disease, stroke, cancers, diabetes, dementia — which kill mainly older people. It is a statement about what people die of, and at what age, rather than about how many of them die.

2. 2

   Distinguish between the demographic transition and the epidemiological transition.

   Model answer

   The demographic transition is about rates: how many births and deaths there are per thousand people per year, and therefore how fast the population grows. The epidemiological transition is about causes: which diseases dominate mortality, and at which ages the deaths fall. The two are linked, because the retreat of epidemic and infectious disease is a large part of why the death rate falls in stage 2 of the demographic transition. But they are not the same thing and must not be treated as versions of one another: a falling death rate is a demographic fact, while a change in what people die of is an epidemiological one. A country can be entirely settled demographically, with birth and death rates both low and stable, and still be moving through further epidemiological change. Conflating the two is the single commonest error on this material.

3. 3

   Describe the stages of the epidemiological transition.

   Model answer

   The age of pestilence and famine: mortality is high and fluctuates violently with epidemics such as plague, cholera and smallpox, with famine and with war; life expectancy is low, roughly between 20 and 40 years, and infant and child deaths make up a very large share of all deaths. The age of receding pandemics: epidemics become less frequent and less lethal as water supply, sanitation, nutrition, housing and later vaccination improve; mortality falls steeply and life expectancy rises to around 50, with the survival of children improving most of all. The age of degenerative and man-made diseases: infectious disease is no longer the principal killer, and deaths are dominated by cardiovascular disease and cancers and by conditions linked to diet, smoking, alcohol, inactivity and pollution; deaths concentrate at older ages and life expectancy exceeds 70. Many writers add a fourth stage, the age of delayed degenerative diseases, in which the same conditions still dominate but treatment and prevention push them to later and later ages, so life expectancy continues to rise into the eighties; treat that fourth stage as a later addition rather than part of the original scheme.

4. 4

   Why do infectious diseases decline first?

   Model answer

   Because they respond to collective public health measures rather than to individual medical treatment, and those measures are comparatively cheap and fast-acting. Piped clean water and sewers break the transmission of cholera, typhoid and dysentery; better and more reliable nutrition raises resistance to infection; better housing reduces overcrowding and the spread of respiratory disease; vaccination removes specific diseases outright. None of these requires a hospital system or an expensive drug regime, and all of them protect children most, which is why infant and child mortality fall earliest and fastest.

5. 5

   Explain why degenerative diseases become the leading causes of death as a country develops.

   Model answer

   Partly by arithmetic and partly by lifestyle. The arithmetic is that once people stop dying of infection in childhood, they live long enough to reach the ages at which heart disease, stroke, cancer and dementia occur; these conditions become dominant in part simply because people are no longer dying of something else first. The lifestyle element is that development itself brings diets high in fat, salt and sugar, smoking and alcohol, sedentary work and motorised travel, obesity and urban air pollution, all of which raise the risk and bring these diseases forward in life. That is why they are labelled man-made as well as degenerative: they are not purely a consequence of growing old.

6. 6

   Can the epidemiological transition stall or run backwards?

   Model answer

   Yes, and treating it as a one-way process is a recognised weakness of the original scheme. The spread of HIV and AIDS through parts of sub-Saharan Africa from the 1990s raised deaths from infectious disease sharply and cut life expectancy by many years in the worst-affected countries. Drug-resistant tuberculosis and malaria remain leading killers. New pandemics can raise infectious mortality anywhere, including in countries long past the receding-pandemics stage. And war, the collapse of health systems and the interruption of vaccination allow old diseases to return. Some writers therefore describe a further stage of emerging and re-emerging infectious disease.

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