Download IDSP Module 7

Uses of epidemiology
Presenter : Ranjana
Moderator : Dr Abhishek
Framework
• History of epidemiology
• Definition
• Uses of epidemiology with examples
Definition of epidemiology
Epidemiology is the study of the distribution
and determinants of health-related events or
states in population groups and the application
of this study to the control of health problems
(Last JM ed. Dictionary of Epidemiology, Oxford University Press, 1995)
• 'Epidemiology is that field of medical
science which is concerned with the
relationship of various factors and conditions
which determine the frequencies and
distributions of an infectious process, a
disease, or a physiologic state in a human
community' (Lilienfeld 1978).
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Comparing the job of a clinician
and the job of an epidemiologist
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The clinician
Deals with patients
Takes a history
Conducts a physical
Makes a diagnosis
Proposes a treatment
Follows up the patient
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The epidemiologist
Deals with populations
Frames the question
Investigates
Draws conclusions
Gives recommendations
Evaluates programmes
Uses of epidemiology
1. Examine causation
2. Study natural history
3. Description of the health status of
population
4. Determine the relative importance of
causes of illness, disability and death
5. Evaluation of interventions
6. Identify risk factors
Uses of epidemiology
1. Examine causation
Genetic
factors
Good health
Environmental factors
(Biological, chemical,
physical, psychological
factors)
Ill health
Life style
related factors
To study historical rise and fall of
disease in the population
• The diseases wax and wane (tuberculosis )
new ones appear (encephalitis,
lethargica,asbestos poisoning ,LSD psychosis)
old ones are eradicated (smallpox) or just
fade away (chlorosis-greenish yellow
discoloration of skin-female adolescent
caused by IDA,miner’s nystagmus).
Number of countries with smallpox,
1967-1978
A Pertussis by 5-Year Age Groups
B. Pertussis by <1, 4-Year, Then 5-Year
Age Groups
Lung Cancer Rates in the United States,
1930–1999
Lung Cancer Rates in the United
States, 1930–1999
Infant Mortality Rates for 2002, by
Race and Ethnicity of Mother
Place
Attack rate of acute hepatitis by zone of
residence, Baripada, Orissa, India, 2004
Attack rate
0 - 0.9 / 1000
1 - 9.9 / 1000
10 -19.9 / 1000
20+ / 1000
Underground water supply
Pump from river bed
Common Source (Vehicle), Single
(Point) Exposure
Outbreak of Cholera, London, AugustSeptember , 1854
Common Source, Continued exposure :
Common Source, interrupted
exposure :
A common source, but the source
introduces the infection into the vehicle only
interruptedly.
• Pseudomonas aeroginosa infection in
urological ward
• A curve will show an increase in frequency
but the curve will be almost flat with
occasional irregular waves coinciding with
the periodic introductions of infection.
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Propogated source
Seasonal fluctuations :
• Malaria and JE are commoner during
immediate post monsoon season.
• Asthma shows highest incidence during
spring and autumn suggesting specific
environmental factors in its causation
Secular trend
Searching for causes and risk factors
• Theories in Primitive and Middle Ages
• “supernatural causes”e.g. being possessed
by evil spirits, wrath of gods, punishment for
evil deeds during previous births and so on).
“bad air”
• contagion theory
• William Farr -“miasma” theory
• Germ Theory -Henle-Koch postulates)
• Epidemiological Wheel Theory
• The Theory of “Necessary” and Sufficient”
cause
Role of the host, the agent and the
environment in the occurrence of disease
Biologic,
Chemical,
Physical (injury, trauma)
Social
Psychological
AGENT
VECTOR
Genotype
Nutrition
Immunity
Behaviour
HOST
Sanitation
Weather
Pollution
Socio-Cultural
Political
ENVIRONMENT
Causes of tuberculosis
Syndrome identification
• Epidemiologists are called “lumpers and
splitters”
• The differentiation of hepatitis A from
hepatitis B and the distinction between
several varieties of childhood leukemia.
• “lumping” include the identification of
many manifestations of tuberculosis.
• Patterson-kelly syndrome of association
between dysphagia and iron deficiency
anaemia but when association was tested by
epidemiological studies , it was not found.
Individual risk and chances:Life tableThe ‘risks’ the average male in England
and Wales
Measures of disease frequency
• Prevalence
 Number of cases of a disease in a defined
population at specified point of time
• Incidence
 Number of new cases, episodes or events occurring
over a defined period of time
Incidence rate
I=
Number of people who get
the disease or condition
in a specified time
Total population at risk
X Factor
Prevalence
P=
Number of people with
the disease or condition
at a specified time
Total population at risk
X Factor
Identify those sections of the population
which have the greatest risk from
specific causes of ill health
Factors associated with
anemia among pregnant women, Orissa, 2004
Characteristics
Univariate
odds ratio
(95% CI)
Adjusted odds
ratio
(95% CI)
Hookworm infestation
12 (5-29)
10 (4-24)
Consumption of IFA < 90 days
4.1 (2-8)
2.7 (1-7)
4 (3-7)
2.3 (1-4)
3.6 (2-6)
1.9 (1-4)
Education below middle school *
Number of pregnancy > 2
* Middle school = Seventh class in Orissa
Community diagnosis :
• The definition of indicators is a pre-requisite
Indicators - to estimate the burden of illness
and the strategies for control.
• The main health indicators are expressed in
terms of crude age-adjusted or age-specific
mortality rates (such as infant mortality
rates, mortality for children under 5, or
maternal mortality rates), disease-specific
morbidity rates, and life expectancy at
birth.
3. Study natural history
Death
Good health
Sub-clinical
disease
Clinical
disease
Recovery
Natural history of disease timeline
4. Evaluation of interventions
Treatment,
Medical care
Good Health
Ill Health
Health promotion
Preventive measures
Public health services
Planning
• Health service administrators should not only
always think of these simple routine
questions, but should be alert to less obvious
potential gaps in coverage.
• For example, the census will state the
numbers of elderly persons who live alone. Is
all or only a small portion of these known to
the public health nurses and others who
provide home surveillance and care?
• Are all needed services available,
accessible, and used appropriately?
Evaluation
• Evaluation is the process of determining, as
systematically and objectively as possible,
the relevance, effectiveness, efficiency, and
impact of activities with respect to
established goals.
• Effectiveness refers to the ability of a
program to produce the intended or
expected results in the field; effectiveness
differs from efficacy, which is the ability to
produce results under ideal conditions.
• Efficiency refers to the ability of the
program to r produce the intended results
with a minimum expenditure of time and
resources.
Description of the health status of
population
Prevalence of anemia among adolescent girls,
Mandla, MP, India 2005
Age in years
12-13
Hemoglobin <12 g%
Number
(%)
71
93.4
Total
76
14-15
88
93.6
94
16-17
71
97.3
73
18-19
27
77.1
31
Total
257
93.8
274
Cumulated bar chart for the breakdown
of many totals in proportions
Proportion (%)
Estimated and projected proportion of
deaths due to non-communicable
diseases, India, 1990-2010
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Injuries
Communicable
diseases
Non communicable
diseases
1990
2000
Year
2010