Basic terminology

• Mortality: levels of (and causes of) death in a population
• Morbidity: levels of (and causes of) illness (rather than death) in a population
• Infectious and parasitic diseases (caused by transmissible agents)
• Chronic and degenerative diseases: (for example, cancers and heart disease)
• Epidemiology: the branch of medical science concerned with disease causation, distribution, occurrence and control

The Epidemiological Transition

• The ‘theory’ of epidemiology transition was first proposed by Abdel Omran
• Levels of illness and death tend to fall with changes in economic development

5 key propositions that underpin the model

• Proposition 1: Mortality is a fundimental factor in population dynamics
• Proposition 2: The transition is characterised by a long term shift through three stages of mortality
• Stage 1: The age of pestilence and famine
• In the richest parts of the world this continues into the 19^th century
• In the poorest parts of the world this continues into the 20^th century
• The period up to 1750 is very reflective of the age of pestilence and famine as there are many infectious diseases
• Stage 2: The age of receding pandemics 1750-1990
• Decline in mortality from infectious diseases, but growth in importance for chronic diseases
• Clear long-term decline in mortality rate
• Stage 3: The age of degenerative and man-made diseases
• Mortality from infectious diseases has depleted
• Increase in mortality from cancers and mental illnesses
• Example: New york showing rise in heart disease and cancer and decline in infectious diseases
• Proposition 3: The epidemiological transition is bias at different moments in time: Favours the young over the old, Favours males over females, favours more affluent members of society
• Proposition 4: Different factors drive the epidemiological transitions at different times
• Proposition 5: Distinctive variations in the pattern, pace, the determinants, and the consequences of population change differenciate 4 basic models of the epidemiological transition.

• 1. The classical or Western model - transition in western societies over past 200 years from high death rates (30 per 1000) to low death rates (10 per 1000), and high birth rates (30 per 1000) to low birth rates (20 per 1000). Gradual mortality decline due to better nutrition and hygiene. During transition, epidemics and infectious diseases declined and degenerative diseases increased. Transition was through all three stages of epidemiological transition.
• 2. Accelerated variant of the classical model - Japan, Eastern Europe and the Soviet Union. Relatively short transition. Mortality began to drop in the 20th century (shift from stage 1 to 2, which is late) due to general social improvements and wide use of abortion. 
• 3. The delayed model - Transition in many poorer countries. Mortality decline delayed until 1930s, 40s 0r 50s. Mortality decline influenced by modern medical technology made avaliable through international agencies (e.g. WHO)
• 4. The transitional model - Transition in some developing countries such as Korea, Hong Kong and Jamacia. Rapid mortality decline in 1940. Introduction of efficient and effective family planning from 1970s, leading to a decline in fertility, suplimented by policies for social development. As a consequence, mortality decline has not slackened in the manner witnessed in the delayed model

Stage 4: Age of delayed degenerative diseases

• Recognises the increase in life expectancy ith improvements in the medical treatment of degenerative diseases 
• Developments are largely concentrated among middle and older age groups, prolonging peoples life spans
• Raises questions regarding quality of life

Stage 5: Age of remerging and re-emerging diseases 

• Recognises the resurgence of infectious and parasitic diseases as a major health threat in the economically developed countries
• Re-emergence of diseases such as tuberculosis, with the bacteria becoming resistant and therefore harder to treat

John Caldwell (1993) proposes 'health transition' rather than 'epidemiological transition'

• Focus on health and survival rather than death
• Suggests that health and mortality are not directly controlled by economic status
• Other factors that may have an effect on the health advances of a country rather than the economy: 1. Educational levels of women of maternal age 2. Family planning practices 3. Educational levels of males
• UN estimate - each additional year of mother's schooling reduces child mortality by at least 3.4%

• In 2015 56% of all deaths were from infectious diseases
• Lower income countries have a higher percentage of deaths by infectious diseases, whereas the higher income countries have more chronic or degenerative deaths
• Thailand has moved through the transition a lot slower than the rest – Thailand has a very large area (574,000) so therefore different parts of the country are moving at different rates through the model

Life expectancy in Hong Kong

• From 1971 to 1990 there is a high increase in the life expectancy for both males and females
• The difference between the life expectancy of males and females becomes smaller – showing how the transitional model is bias to males  

Two touchstone diseases of epidemiological transition

• Pulmonary tuberculosis (infectious disease)
• Cardio-vascular disease (chronic illness)

Coefficient of variation

• Increasing CV: increase in the country to country variability of mortality 
• Decreasing CV: decrease in the country to country variability of mortality

• Through the 20^th century country became increasingly similar in the mortality rates of cardio-vascular disease. But became increasingly variable in the mortality rates of Tuberculosis. 
• D.R.Philips (1994) "Does epidemiological transition have utility for health planners" - 3 Key Points: 1. The theory of epidemiological transition is of only limited utility in the detailed planning of health and health care delivery. 2. The utility of the theory of epidemiological transition increasingly calls for a consideration of patterns of morbidity as well as mortality in a population. 3. Within any developing country, there may be a variety of epidemiological transitions in operation, dependent on the area of the country, the social class of the population, levels of urbanisation etc.
• Phillips argues: In developing countries, epidemiological transition culd provide a practical framework for discussions with agencies involved in the provison of assistance in health and health-related areas. Epidemiological transition may form the basis for shifts in health sector resource allocation. By implication, epidemiological transition may be used to plan for changes in the training of medical personnel and the manufacture of medicines and equipment.
• Mechanisms that ‘drive’ the transition (Omran refers to the ‘modernization complex’. But what causes the changes (sanitary reform, public health, diet and nutrition, etc.)? LIMIT TO THE PREDICTIVE POWER OF THE MODEL – the model is too general
• Can the transition ever be considered to be complete (as reflected in the various extensions to the original model)?
• The model is limited by the availability and quality of the mortality data available for many geographical areas.
• Patterns of morbidity differ to patterns of mortality in a population – EPIDEMIOLOGICAL TRANSITION MAY NOT BE APPLICABLE TO PATTERNS OF ILLHEALTH (AS OPPOSED TO DEATH) IN A POPULATION.

The Epidemiologic Transition: A Theory of the Epidemiology of population change

• Degenerative and man made diseases displace pandemics of infection as the primary causes of morbility 
  
• There is a gradual change in the mortality from younger to older ages
• The first epidemiological tranisiton occured 100 centuries ago when man moved towards the agricultural society. As cities grew, and exploration of the surrounding world increased, man spread deadly diseases in ever-greater numbers - the age of pestilence and famine. Some developing countries are still in this stage
• The second epidemiological transition began around 200 years ago, with the industrial revolution. Fertility rates are high so population is growing rapidly. 
• Little population growth in the third stage. Such a long life expectancy also means a relatively long period of morbidity. Increased demand for health care related to diseases of older people

Evolution of the "fourth stage" of epidemiologic transition in people aged 80 years and over: population based cohort study using electronic health records

• In middle- and low-income countries, the emergence of HIV-related mortality and the impact of war and civil conflict show that changes in mortality are not always consistent with the direction of theory 
• Morbidity, the incidence of diseases and health conditions, have generally been omitted from direct consideration
• Data were obtained from the Clinical Practice Research Datalink which has been shown to be representative of the UK population with respect to age, gender, and geographical distribution.
• 300,000 participants
• Cause-specific proportional hazards models were used to estimate hazard ratios for incidence rates over time.
• Between 1990 and 2014, the male-to-female ratio among individuals aged 80 to 95 years increased. A lower risk of coronary heart disease, stroke and chronic obstructive pulmonary disease was observed among 80–84 year-olds in 2010–2014 compared to 1995–1999. By contrast, the risk of type II diabetes, cancer, dementia, cognitive impairment, and musculoskeletal pain was greater in 2010–2014 compared to 1995–1999.
• Redistribution of the over-80 population to older ages, and declining age-specific incidence of cardiovascular and respiratory diseases in over-80s, are consistent with the “fourth stage” of epidemiologic transition, but increases in diabetes, cancer, and age-related impairment show new emerging epidemiological patterns in the senior elderly.