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Why treat people….
…without changing what makes them sick?
Why
does a disease
develop
in some people
and not in others?
Epidemiology
Dr Prasanna Thirunavukkarasu
Premise	
  underlying	
  Epidemiology
Disease, Illness, and Ill health
are not randomly distributed in human populations
Each of us has certain characteristics
that predispose us to, or protect us against
a variety of different diseases
These characteristics
may be primarily genetic in origin or
may be the result of exposure to certain environmental hazards
Perhaps most often, an interaction of genetic and environmental factors
Epidemiology
Study of the distribution and determinants
of health-related states or events
in specified populations
and the application of this study
to control of health problems
Study of how disease
is distributed in populations and
the factors that influence or
determine this distribution
Epidemiology
Epidemiology
Study of the distribution and determinants
of health-related states or events
in specified populations
and the application of this study
to control of health problems
Three closely interrelated components
Frequency
Distribution
Determinants
Three closely interrelated components
Frequency
Distribution
Determinants
Frequency
Disease / Disability / Death
Health related Events / States
Developing definition of disease
Instituting mechanism for counting cases
Determining the size of the population
Rates / Ratios
Three closely interrelated components
Frequency
Distribution
Determinants
Distribution
Person, Place, Time
Variation / Patterns
Descriptive Epidemiology
Generates hypotheses
Three closely interrelated components
Frequency
Distribution
Determinants
Determinants
Determinants
Tentative explanation for an observation - hypothesis
Analytical Epidemiology
Tests hypothesis
Three closely interrelated components
Frequency
Distribution
Determinants
Fourth Component - Unique to Epidemiology
Human Population
Population
Common Identifiable Characteristic
Denominator
Three closely interrelated components
Frequency
Distribution
Determinants
Fourth Component - Unique to Epidemiology
Human Population
Fifth Component - Application
Disease Control / Prevention
Disease Control / Prevention
Continuous Monitoring
Objectives of Epidemiology
1 to identify the etiology or cause of a disease and the relevant risk
factors—that is, factors that increase a person’s risk for a disease
2 to determine the extent of disease found in the community
3 to study the natural history and prognosis of disease
4 to evaluate both existing and newly developed preventive and
therapeutic measures and modes of health care delivery
5 to provide the foundation for developing public policy relating to
environmental problems, genetic issues, and other considerations
regarding disease prevention and health promotion
Aims of Epidemiology
1. to describe the distribution and magnitude of health and
disease problems in human populations
2. to identify aetiological factors (risk factors) in the pathogenesis
of diseases
3. to provide the data essential to the planning, implementation
and evaluation of services for the prevention, control and
treatment of disease and to the setting up of priorities among
those services
Ultimate Aim of Epidemiology
• to eliminate or reduce the health problems or its consequences
• to promote the health and well-being of society as a whole
A Multistep Process
	
  Epidemiologic	
  Reasoning
The first step is to determine whether an association exists between
exposure to a factor (e.g., an environmental agent) or a characteristic of
a person (e.g., an increased serum cholesterol level) and the
development of the disease in question.
The second step is to try to derive appropriate inferences about a
possible causal relationship from the patterns of the associations that
have been found
Epidemiologic Reasoning
• Process begins with the suspicion
• Possible influence of a particular factor
on the occurrence of the disease
Suspicion may arise from
Clinical Practice
Examination of Disease Patterns
Observations from Laboratory Research
Theoretical Speculations
Epidemiologic Approach
Asking Questions
Making Comparisons
Asking Questions
Related to Health Events
What is the event?
Where did it happen?
When did it happen?
How much is the magnitude ?
Why did it happen ?
So, what is to be done?
Asking Questions
Related to Health Action
What can be done to reduce the problem and its consequences?
How can it be prevented in the future?
What action should be taken by the community? By the health
services? By other sections? Where and for whom these activities be
carried out?
What resources are required? How are the activities to be organised?
What difficulties may arise, and how might they be overcome?
Making Comparisons
Between
Two subgroups in the population
Affected and Not Affected
Exposed and Not Exposed
Intervention and Without Intervention
Comparability
Standarisation
The Epidemiologic Approach
How does the epidemiologist proceed to identify the cause of a disease?
Epidemiology often begins with descriptive data
The first question to ask when we see
differences between two groups or two regions or over time is,
“Are these differences real?”
Are the data from each area of comparable quality?
Before we try to interpret the data, we should be satisfied that the data are valid.
If the differences are real, then we ask,
“Why have these differences occurred?”
Are there environmental differences between high-risk and low-risk areas, or
are there differences in the people who live in those areas?
This is where epidemiology begins its investigation!!
Subspecialties
• Disease-Specific
Reproductive Epidemiology, NCD Epidemiology, Infectious Disease Epidemiology, Cancer
Epidemiology, Psychiatric Epidemiology
• Exposure-Specific
Environmental Epidemiology, Behavioural Epidemiology, Nutritional Epidemiology
• Population-Specific
Geriatric Epidemiology
Determinants - Molecular Epidemiology, Genetic Epidemiology
Vs. Social Epidemiology (Biological / Societal level)
Psycho Endo Neuro Immunology
Study of the interaction between psychological
processes and the nervous and immune systems
of the human body
Introduction to Epidemiology
Social Inequity - Psychobiological Mechanism - Illness
People’s perception & experience of their place
in social hierarchies
Stress from the ‘Social Environment’
Affects Neuroendocrine functions
Alters host susceptibility
Increases human’s vulnerability to disease
Epidemiology
Dr Prasanna Thirunavukkarasu
Assistant Professor
IGMCRI
(Govt. of Puducherry)
+919843172412
drprasanmail@gmail.com

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Introduction to Epidemiology

  • 1. Why treat people…. …without changing what makes them sick?
  • 2. Why does a disease develop in some people and not in others?
  • 4. Premise  underlying  Epidemiology Disease, Illness, and Ill health are not randomly distributed in human populations Each of us has certain characteristics that predispose us to, or protect us against a variety of different diseases These characteristics may be primarily genetic in origin or may be the result of exposure to certain environmental hazards Perhaps most often, an interaction of genetic and environmental factors
  • 5. Epidemiology Study of the distribution and determinants of health-related states or events in specified populations and the application of this study to control of health problems
  • 6. Study of how disease is distributed in populations and the factors that influence or determine this distribution Epidemiology
  • 7. Epidemiology Study of the distribution and determinants of health-related states or events in specified populations and the application of this study to control of health problems
  • 8. Three closely interrelated components Frequency Distribution Determinants
  • 9. Three closely interrelated components Frequency Distribution Determinants
  • 10. Frequency Disease / Disability / Death Health related Events / States Developing definition of disease Instituting mechanism for counting cases Determining the size of the population Rates / Ratios
  • 11. Three closely interrelated components Frequency Distribution Determinants
  • 12. Distribution Person, Place, Time Variation / Patterns Descriptive Epidemiology Generates hypotheses
  • 13. Three closely interrelated components Frequency Distribution Determinants
  • 15. Determinants Tentative explanation for an observation - hypothesis Analytical Epidemiology Tests hypothesis
  • 16. Three closely interrelated components Frequency Distribution Determinants Fourth Component - Unique to Epidemiology Human Population
  • 18. Three closely interrelated components Frequency Distribution Determinants Fourth Component - Unique to Epidemiology Human Population Fifth Component - Application Disease Control / Prevention
  • 19. Disease Control / Prevention Continuous Monitoring
  • 20. Objectives of Epidemiology 1 to identify the etiology or cause of a disease and the relevant risk factors—that is, factors that increase a person’s risk for a disease 2 to determine the extent of disease found in the community 3 to study the natural history and prognosis of disease 4 to evaluate both existing and newly developed preventive and therapeutic measures and modes of health care delivery 5 to provide the foundation for developing public policy relating to environmental problems, genetic issues, and other considerations regarding disease prevention and health promotion
  • 21. Aims of Epidemiology 1. to describe the distribution and magnitude of health and disease problems in human populations 2. to identify aetiological factors (risk factors) in the pathogenesis of diseases 3. to provide the data essential to the planning, implementation and evaluation of services for the prevention, control and treatment of disease and to the setting up of priorities among those services
  • 22. Ultimate Aim of Epidemiology • to eliminate or reduce the health problems or its consequences • to promote the health and well-being of society as a whole
  • 23. A Multistep Process  Epidemiologic  Reasoning
  • 24. The first step is to determine whether an association exists between exposure to a factor (e.g., an environmental agent) or a characteristic of a person (e.g., an increased serum cholesterol level) and the development of the disease in question. The second step is to try to derive appropriate inferences about a possible causal relationship from the patterns of the associations that have been found
  • 25. Epidemiologic Reasoning • Process begins with the suspicion • Possible influence of a particular factor on the occurrence of the disease Suspicion may arise from Clinical Practice Examination of Disease Patterns Observations from Laboratory Research Theoretical Speculations
  • 27. Asking Questions Related to Health Events What is the event? Where did it happen? When did it happen? How much is the magnitude ? Why did it happen ? So, what is to be done?
  • 28. Asking Questions Related to Health Action What can be done to reduce the problem and its consequences? How can it be prevented in the future? What action should be taken by the community? By the health services? By other sections? Where and for whom these activities be carried out? What resources are required? How are the activities to be organised? What difficulties may arise, and how might they be overcome?
  • 29. Making Comparisons Between Two subgroups in the population Affected and Not Affected Exposed and Not Exposed Intervention and Without Intervention Comparability Standarisation
  • 30. The Epidemiologic Approach How does the epidemiologist proceed to identify the cause of a disease?
  • 31. Epidemiology often begins with descriptive data The first question to ask when we see differences between two groups or two regions or over time is, “Are these differences real?” Are the data from each area of comparable quality? Before we try to interpret the data, we should be satisfied that the data are valid. If the differences are real, then we ask, “Why have these differences occurred?” Are there environmental differences between high-risk and low-risk areas, or are there differences in the people who live in those areas? This is where epidemiology begins its investigation!!
  • 32. Subspecialties • Disease-Specific Reproductive Epidemiology, NCD Epidemiology, Infectious Disease Epidemiology, Cancer Epidemiology, Psychiatric Epidemiology • Exposure-Specific Environmental Epidemiology, Behavioural Epidemiology, Nutritional Epidemiology • Population-Specific Geriatric Epidemiology Determinants - Molecular Epidemiology, Genetic Epidemiology Vs. Social Epidemiology (Biological / Societal level)
  • 33. Psycho Endo Neuro Immunology Study of the interaction between psychological processes and the nervous and immune systems of the human body
  • 35. Social Inequity - Psychobiological Mechanism - Illness People’s perception & experience of their place in social hierarchies Stress from the ‘Social Environment’ Affects Neuroendocrine functions Alters host susceptibility Increases human’s vulnerability to disease
  • 36. Epidemiology Dr Prasanna Thirunavukkarasu Assistant Professor IGMCRI (Govt. of Puducherry) +919843172412 drprasanmail@gmail.com