A world in transition

1
A world in transition

• Objectives of lecture
• To present the theory on epidemiological
  transition (Omran, 1971)
• To discuss the actual relevance and usefulness of
  Omrans theory

2
Population age structure USA, 1900 1995
Shift in population age structureDemographical
transition
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Expectancy of life

• Average life expectancy for a girl born in the
  Central African Republic and Japan is 48 years
  and 81 years, respectively
• Average life expectancy is projected to increase
  in many countries
• Today estimated 380 220 mill persons ? 65 yrs
  in developed developing countries, respectively
• In 2020, pop projected to reach 690 460 mill
  persons ? 65 yrs in developed developing
  countries, respectively
• This is mainly due to a decrease in infectious
  diseases pushed by better water sanitation,
  immunisation and a well functioning network of
  health services
• The price to pay is an increase in chronic
  conditions such as cancer, circulatory disease,
  muscolo-skelatal disease, chronic respiratory
  disease and mental disorders
• This is called the health transition or
  epidemiological transition (ET)

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Life expectancy by region, 1955-1997
Female
Male
Years
Years
Source GBD 2000
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ET Changes in fertility and mortality with
modernisation

• Abdel Omran The epidemiological transition A
  theory of the epidemiology of population change.
  Milbank Quarterly (1971) 49, 509-538
• Shift of focus of epidemiology from a single
  disease to the systems of disease

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Epidemiology - classic approach

• Psychiatric epidemiology
• Diabetes epidemiology
• Cardivascular epidemiology
• Cancer epidemiology
• Infectious disease epidemiology

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A change in focus

• Instead at looking at individual diseases, we
  need to look at the patterns of diseases

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Demographic transition
Preposition One Mortality is the fundamental
factor in the dynamics of population growth
Interplay between fertility and mortality
?When mortality drops this will subsequently be
followed by a drop in birth rates This interplay
takes place when population has started to grow
exponentially
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Demographic transition
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Q What are the possible reasons for a decrease
in fertility as a consequence of a drop in
overall mortality?
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Epidemiological transition (ET)
Preposition Two In ET, a long-term shift occurs
in mortality and disease patterns where pandemics
of infection are replaced by non-communicable and
man-made diseases (latter term later later
defined by Omran as radiation injury, mental
illness, drug dependency, traffic accidents,
occupational hazards) Omran found a very
consistent pattern - As the rate of infectious
diseases goes down, the population ages, one sees
an emergence of non-communicable disease
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Omrans classic (western) three-stage model on
mortality patterns (Preposition Two)

• Age of pestilence and famine
• Age of receding pandemics
• Age of degenerative and man-made disease

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I. Age of pestilence and famine
Characterised by high mortality rates, wide
swings on mortality rate, little population
growth and very low life expectancy (20-40
years), most people die of infectious diseases
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II. Age of receding pandemics
Epidemics become less frequent, infectious
diseases in general become less frequent, start
of exponential population growth, increase in
life expectancy from apx. 30 to 50 years, a slow
rise in degenerative/non-communicable diseases
begins to appear
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III. Age of degenerative and man-made disease
Low rate of infectious diseases, longer life
expectancy (gt 50 years), fertility becomes
driving factor in population growth, little death
caused by infectious disease, most people die of
degenerative/non-communicable diseases
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ET
Preposition Three As ET moves on, the most
pronounced changes in health are seen among
children and young mothers Preposition
Four The shifts in disease patterns during ET
are closely related to the demographic and
socio-economic transition which takes place due
to modernisation
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Preposition FiveThree ET modelsa) Classic
(Western)b) Acceleratedc) Delayed

• Age of pestilence and famine
• Age of receding pandemics
• Age of degenerative and man-made disease

Q According to Omran, what changes resulted in
a shift in the disease/mortality pattern from one
phase to the next in the classic, accelerated and
delayed model? - In mid/high-income
communities? - In low-income communities?
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(LaPorte, R., 2003)
?
Accidents
?
Diabetes (NID)
?
Coronary heart Dis.
Cancer
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Projected trends in cause of deaths in developing
countries
(Murray Lopez, 1996)
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(LaPorte, R., 2003)
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(LaPorte, R., 2003)
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Epidemiological transition as a theory - lets
take it apart.

• Q What are the limitations in this model based
  on a linear progression of phases (the 3 ages)?

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Urbanisation

• Another major driving factor in ET is
  urbanisation
• Urbanisation is of specific importance in
  developing countries
• During the time of modernisation a migration
  from rural to urban areas results in a shift in
  risk factors which again may result in a change
  in disease patterns and mortality ET
• Q What possible risk factors are related to
  urbanisation?
• - in developing countries?
• - in developed countries?

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Vietnam - Infant Mortality Rate
(Population Reference Bureau, Vietnam, 2001)
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Migration

• Within countries
• Between countries
• Within continents
• Between continents
• Causes
• Improved educational/economical opportunities
• War
• Political
• Biological/climatic

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New emerging communicable diseases
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Projected population age structure with without
AIDS, Botswana, 2020
Projected population structure with and without
the AIDS epidemic, Botswana, 2020
(US Census Bureau, World Population Profile 2000)
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The dynamics of ET will depend on differences in
population strata re SES, geography etc.

• In the urban areas, life expectancy will
  increase, people die of diseases driven by life
  style and age-related causes
• In the rural areas, many people (specifically
  children) still die of infectious diseases
• The double burden
• Can you think of other scenarios - beside the
  urban/rural setting - which will result in a
  double burden?

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Double burden the health system

• Emerging diseases with no former local history
  regarding
• Data on disease burden (monitoring prevalences,
  incidences, high risk groups/risk factors)
• Preventive measures (e.g. costs, strategies,
  means of health communication, target groups)
• Diagnostics (e.g. decision making, costs, staff,
  equipment)
• Treatment (e.g. decision making, costs, staff)
• Priorities in specific disease intervention in a
  low-income double-burden community?

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ET - case definitions?

• Q What are the limitations in a model which
  operates with two categories of disease
  (infectious non-communicable/chronic disease)?

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The division between infectious and
chronic/non-communicable disease

• From an intervention perspective, the division
  between infectious and chronic disease is not
  very useful
• Many of the risk factors and causes are closely
  interrelated
• Examples
• Some chronic illnesses such as certain types of
  cancer and rheumatic heart disease are caused by
  infections
• Long term physical illness caused by infectious
  diseases will often lead to psychological
  problems
• Psychological problems can directly
  (immuno-mediated?) and indirectly (socio-economic
  decline) increase the risk of acquiring other
  types of disease
• Therefore, when dealing with intervention the two
  types of disease must be addressed simultaneously

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ET - so what?

• The need for development of a systems approach to
  epidemiology
• I.e. a system or model which can describe and
  predict the interplay of factors that cause one
  disease to increase while another falls
• To understand the diseases in a community or
  country it is critical to begin to think in ET -
  where no disease stands alone but is part of a
  complex scenario of risk factors with often very
  specific geographical characteristics

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ET - a summary

• The epidemiological transition will result in a
  major global dramatic change in disease specific
  morbidity and mortality patterns
• Due to changes in age structure, urbanisation and
  the new life style related risk factors,
  developing countries will face new health
  problems of unseen dimensions
• Health authorities in developing (and developed)
  countries have to shift their focus and resource
  allocation from communicable to non-communicable
  diseases
• BUT at the same time they have to meet the need
  of the rural populations where millions of
  individuals will still suffer and die from simple
  preventive and curable infectious diseases
• The HIV/AIDS/TB epidemic is a very different
  story with unknown consequences