Epidemiological_demographic Transition_Theory_

Epidemiological and demographic transition theory

1. Epidemiological Transi tion Theory: Patterns, Factors, and Modern Relevance

2. Introduction to Epidemiological Transition The process of change in mortality rate, along with the change in causes of death, is termed as epidemiological transition Epidemiological transition describes the shift in disease and mortality patterns over time. The early periods of civilisation have witnessed more deaths caused by infectious diseases, natural calamities, and a lack of food supply. These factors were replaced by deaths due to other morbid conditions, such as lifestyle diseases and non-communicable diseases (NCDs). Proposed by Abdel R. Omran in 1971, to denote the change in disease patterns and causes of death within a population linking health, demography, and development.

3. Concept of Epidemiology Epidemiology- Derived from the Latin word : epi (upon), demos (people), logos (study) and refers to studying what ‘comes upon’ a population Focuses on patterns, causes, and effects of health and disease conditions in populations. Aims to control and prevent diseases by studying their distribution and determinants. There are two major components of the transition: (1) changes in population growth trajectories and composition, especially in the age distribution from younger to older, (2) changes in patterns of mortality, including increasing life expectancy and reordering of the relative importance of different causes of death

4. Omran’s Epidemiological Transition Theory (1971) It states that during the transition, a long-term shift occurs in mortality and disease patterns whereby degenerative and man-made diseases gradually displace pandemics of infection as the chief form of morbidity and the primary cause of death. The theory also emphasises the age and sex structure of the population , suggesting that during the epidemiological transition, the most profound changes in health and disease patterns happen among children and young women. Three main stages mark this transition process. He established that there exists a strong association between the mortality rate and the cause of death , especially in the form of diseases.

5. Mortality patterns distinguish three major successive stages of the epidemiological transition: Age of Pestilence and Famine – high, fluctuating mortality; the average life expectancy at birth is low and variable, fluctuating between 20 and 40 years. Age of Receding Pandemics – 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 years to about 50 years, with mortality declining. Age of Degenerative and Man-Made Diseases – characterised by continuous decline in mortality and eventually approaching stability at a relatively low level. The average life expectancy at birth rises until it exceeds 50 years. It is during this stage that fertility becomes the crucial factor in population growth .

6. Omran’s Model of Epidemiological Transition The graph shows mortality decline across three stages. X-axis: Time →, Y-axis: Mortality rate ↓ Curve demonstrates transition from infectious to degenerative diseases.

7. Models of Epidemiological Transition Classical/Western Model – describes the gradual, progressive transition from high mortality (above 30 per 1,000 population) and high fertility (above 40 per 1,000) to low mortality (less than 10 per 1,000) and low fertility (less than 20 per 1,000) gradual, socioeconomic-led transition (e.g., Europe). In the late phase of the classical transition, degenerative and man-made diseases displaced infections as the leading causes of mortality and morbidity.

8. Accelerated Model – describes the rapid mortality transition that occurred most notably in Japan. Rapid change due to modernisation . National and individual motivations favoured a controlled rate of population growth increase and provided the intense encouragement needed to lower fertility in a relatively short period of time. Contemporary/Delayed Model – incomplete, mixed transitions (e.g., developing countries). Public health measures through imported, internationally sponsored medical packages have been instrumental in lowering mortality in these countries while leaving Fertility at substantially high levels. However, infant and childhood mortality remain excessively high in most of these countries. Most of the countries in Latin America, Africa, and Asia fit this model

9. Horiuchi’s Five-Stage Model (2000s) Horiuchi proposed that each transition period is marked by a significant change in the cause of death. This change, according to him, is directly or indirectly related to the changes in industrial technology. The five major stages of epidemiological transition: 1. First epidemiological transition , which is marked by infectious diseases being the prime cause of death in populations. 2. Second epidemiological transition , where degenerative diseases became the main cause of death. 3. Third epidemiological transition, in which non-cardiovascular degenerative diseases were responsible for the maximum deaths. 4. Fourth epidemiological transition , which is a future stage in which a decrease in non-cardiovascular degenerative diseases like cancer is observed. 5. Fifth epidemiological transition , which marks another future stage wherein the natural ageing process is slowed down in the population .

10. Relation with Demographic Transition Both demographic and epidemiological transitions occur with modernisation . Demographic transition tracks fertility and mortality decline. Epidemiological transition explains the changing causes of death accompanying it. Demographic transition shows how birth rate and death rates are subsequently changed over the period of time and their impact on the age-sex structure of the population. Maternal and child health improved, reducing the infant mortality rate. This led to an increase in life expectancy of the population, thus, eventually, increasing elderly people in the population who are more prone to NCDs than younger people. Public health campaign, awareness, and socio-economic development helped to achieve high life expectancy https://youtu.be/JMRnWDhGWBg

11. Linking Demographic and Epidemiological Transiti ons Diagram shows overlapping curves of birth rate, death rate, and disease types. Highlights how mortality decline precedes fertility decline. Indicates rising NCDs as infectious diseases fall.

12. Factors Influencing Epidemiological Transition Demographic changes – These are changes in both mortality and fertility. improved survival and ageing populations. The young population will also be exposed to diseases that more frequently affect elderly people, such as cancer and cardiovascular diseases Changes in risk factors : The risk factors involved in epidemiological transition can be broadly categorised as biological factors (microorganisms, environmental factors, social, cultural and behavioural factors, and the practices of modern medicine The biological factors involve changes in microorganisms that enable them to cope with an increasingly hostile environment and are mainly clinical in nature, such as the development of new strains of influenza virus affecting all ages Environmental factors- environmental sanitation, particularly a clean water supply, sanitary disposal of waste and proper housing Social and behavioural factors – urbanisation , diet, lifestyle. Medical advancements – vaccines, antibiotics, public health systems.

13. Global Patterns and Variations Developed nations: chronic diseases and aging populations dominate. Developing nations: double burden of infectious and chronic diseases. Sub-Saharan Africa and South Asia lag due to persistent infections and poverty.

14. Regional Epidemiological Transitions Europe: major gains in life expectancy, dominance of CVDs. Central Asia: mortality fluctuations due to conflict and CVDs. Southeast Asia: NCDs rising with globalisation and urban lifestyles .

15. Epidemiological Transition in India India faces a dual burden—infectious and non-communicable diseases. Vaccination and public health have improved survival since the 1970s. NCDs like cardiovascular disease, diabetes, and hypertension now dominate mortality patterns.

16. Recent Trends in India MCCD (Medical certification of cause of death ) Report 2020 Circulatory diseases: 32.1% of medically certified deaths. Respiratory diseases: 10%; COVID-19: 8.9%. Higher male mortality in respiratory and injury-related causes.

17. Critiques and Limitations of the Theory Transition is not uniform or unidirectional. New infectious diseases (e.g., HIV, COVID-19) can reverse progress. Socioeconomic and environmental inequalities distort global patterns.

18. Impact of Globalisation Lifestyle changes (diet, inactivity) accelerate NCD growth. Urbanisation and migration increase mental health and pollution-related diseases. International health programs shape mortality trends in developing countries.

19. Public Health Implications Focus shifts from infectious disease control to chronic disease prevention. Health systems must address ageing populations and long-term care. Education and behavioural change campaigns are crucial.

20. Case Study: COVID-19 and Reverse Transition COVID-19 disrupted progress in mortality decline globally. Exposed vulnerabilities in health systems even in developed nations. Illustrates cyclical nature of epidemiological transition.

21. Key Takeaways Epidemiological transition links mortality, health, and societal development. Omran’s theory evolved with new models and global realities. Public health policies must balance infectious and chronic disease challenges. https://youtu.be/4oaQUAnA6nY?si=gPzLJwe_ApZqfc_v