What is the epidemiological transition, and how is it measured?

The epidemiological transition is a shift in the pattern of health and disease due to societal and technological changes.

The epidemiological transition theory, first proposed by Abdel Omran in the 1970s, describes how the cause of death in a population changes as a society develops. It is a part of the broader demographic transition model, which looks at how birth and death rates change over time due to development.

In the first stage of the epidemiological transition, often referred to as the 'Age of Pestilence and Famine', mortality is high and fluctuating, life expectancy is low and variable, and the main causes of death are infectious and parasitic diseases. This stage is typically associated with pre-industrial societies.

The second stage, the 'Age of Receding Pandemics', sees a gradual decline in mortality as improvements in sanitation, nutrition and medicine lead to a decrease in infectious and parasitic diseases. Life expectancy increases and the population begins to grow rapidly.

The third stage, the 'Age of Degenerative and Man-Made Diseases', is characterised by a further decline in mortality and a shift in the leading causes of death from infectious diseases to chronic and degenerative diseases, such as heart disease and cancer. This stage is associated with industrialised societies.

Some scholars propose a fourth stage, the 'Age of Delayed Degenerative Diseases', where life expectancy continues to increase due to medical advances that delay the onset of chronic diseases. Others suggest a fifth stage, where infectious diseases re-emerge as major health threats due to factors such as antibiotic resistance and globalisation.

The epidemiological transition is measured using health data, including mortality rates, cause of death statistics, and life expectancy figures. These data can be analysed to identify patterns and trends, and to compare different societies and periods. For example, a society in the first stage of the epidemiological transition would have a high mortality rate, a low life expectancy, and a high proportion of deaths from infectious diseases, while a society in the third stage would have a low mortality rate, a high life expectancy, and a high proportion of deaths from chronic diseases.