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SEMINAR

EPIDEMIOLOGYDEFINITION , SCOPE ,APPROACH ,MEASUREMENTS

Presented by:

Dr Nikita Sharma

Assisstant Professor

Dept .of Community

Medicine,MGMCH,Jaipur

Epidemiology is the basic science of Preventive

and Social Medicine.

• Epidemiology is scientific discipline of public

health to study diseases in the community to

acquire knowledge for health care of the society.

(prevention, control and treatment).

Epidemiological principles and methods are applied in

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- Clinical research,

- Disease prevention,

- Health promotion,

- Health protection and

- Health services research.

• The results of epidemiological studies are also used

by other scientists, including health economists, health

policy analysts, and health services managers.

DEFINITION

“The study of the distribution and determinants of health-

related states or events in specified populations, and the

application of this study to the prevention and control of

health problems”

As defined by John M. Last (1988)

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DISTRIBUTION

• Distribution of disease occurs in a PATTERN.

• PATTERN- Time, Place, Person

. • PATTERN – Hypothesis for Causative/Risk factor –

Etiological Hypothesis. • Descriptive Epidemiology.

PERSON

• AGE

• SEX

• RACE

• SOCIO ECONOMIC STATUS

• RESIDENCE

• MARITAL STATUS

• OCCUPATION

BIMODALITY

There may be two separate peaks instead of

one in the age incidence curve of a disease.

This is known as bimodality as seen in

Hodgkin’s lymphoma, breast cancer.

It indicates that there are two different sets of

causative factors even though the clinical and

pathological manifestations of the disease is

the same in all ages

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PLACE

• International

• National

• Urban/rural difference

• Localised pattern of disease

MIGRATION STUDIES

The use of migrant studies is a way of distinguishing

genetic and environmental factors.

Carried out in 2 ways-

1) Study of genetically similar groups but living

under different environmental conditions. Eg: Twins

2) Study of genetically different groups living in a

similar environment.

Eg: Men of Japanese origin living in USA have higher

rate of coronary heart disease than the Japanese in

Japan

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COMMON SOURCE EPIDEMICS

1) Single exposure-

It can occur due to an infectious agent or as a result of

contamination of the environment and develops within

one incubation period.

Eg: Bhopal gas tragedy, Minamata disease

The epidemic curve rises and falls rapidly, usually has

one peak

It tends to be explosive (i.e. clustering of cases within a

short time)

CONTINUOUS EXPOSURE

It is when the exposure from the same source is

prolonged and the epidemic continues over more than

one incubation period.

The epidemic reaches a sharp peak, but tails off

gradually over a longer period of time.

Eg: A well of contaminated water or nationally

distributed vaccine(polio vaccine) or food; water borne

cholera.

PROPAGATED EPIDEMICS

Types- person to person, arthropod, animal

The epidemic shows gradual rise and tails

off over a much longer period of time

It is more likely to occur where there is

i) regular supply of new susceptible

individuals- Births, Immigrants

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PERIODIC FLUCTUATIONS

1) Seasonal trend- Seasonal variation is

characteristic of many communicable diseases.

Eg: Measles, upper respiratory tract

infections(seasonal rise during winter), Malaria,

etc.

Non-infectious diseases and conditions may

sometimes exhibit seasonal variation.

Eg: Sunstroke, hay fever.

2) Cyclic trend- Some diseases occur in cycles

spread over short periods of time (days, weeks,

months or years) .

Eg:

Influenza pandemics are known to occur at

intervals of 7-10yrs due to antigenic variations.

Non-infectious conditions may also occur in this

trend. Eg: Automobile accidents in the US are

more frequent on weekends.

C) LONG TERM TRENDS /SECULAR

TRENDS

It refers to changes in the occurrence of

disease over a long period of time.

Eg: Coronary disease, diabetes showing

consistent upward trend and

a decline in TB, polio in developed countries

during the past 50 yrs.

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DETERMINANTS

• Identifying the causes and risk factors for diseases.

• Testing the Hypothesis

• Analytical Epidemiology

SCOPE OF EPIDEMIOLOGY

1. Causation of the disease.

• 2. Natural history of the disease.

• 3. Health status of the population.

• 4. Evaluation of Interventions.

CAUSATION OF THE DISEASE.

• Most of diseases are caused by interaction

between genetic and environmental factors.

(Diabetes)

• Personal behaviors affect this interplay.

• Epidemiology is used to study their influence

and the effects of preventive interventions

through health promotion.

EPIDEMIOLOGICAL TRIAD OF TBA cause of a disease is an event,

condition, characteristic, or

combination of these factors which plays

an important role in producing the

disease. •

A cause could be sufficient

or necessary

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HEALTH STATUS OF THE POPULATION

• Epidemiology is often used to describe the

health status of population.

• Knowledge of the disease burden in

populations is essential for health

authorities.

• To use limited resources to the best possible

effect by identifying priority health

programmes for prevention and care.

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EVALUATION OF INTERVENTIONS

• To evaluate the effectiveness and efficiency of health

services.

• This means determining things such as – -

- Impact of Contraceptive use on Population Control.

- -the efficiency of sanitation measures to control

diarrheal diseases and

- the impact of reducing lead additives in petrol.

EPIDEMIOLOGIC APPROACH

1. Identify a PROBLEM –determine the extent and

magnitude of problem

2. Formulate a HYPOTHESIS ( asking the right

question ) ; ; good hypotheses are: Specific, Measurable,

and Plausible

3. TEST that HYPOTHESIS( assumptions vs. type

of data )

4. always Question the VALIDITY of the result(s) :

: Chance ; Bias

Asking questions Related to Health Events

. What is the event? (Problem)

2. What is magnitude?

3. Where did happen?

4. When did happen?

5. Who are affected?

6. Why did it happen?

Related to Health Action

1. What can be done to reduce the problem?

2. How can be prevented in future?

3. What action should be taken by community?

4. What resources required?

5. How activities to be organized?

6. What difficulties may arise?

Epidemiology is “a means of learning by asking questions

and getting answers that lead to further questions.”

TOOLS OF MEASUREMENTS

Basic tools are –

• 1. Rate

• 2. Ratio

• 3. Proportion

• Used for expression of disease magnitude.

RATE

• A “Rate” measures the occurrence of some

specific event in a population during given

time period.

• Example

Death Rate = total no of death in 1 yr / Mid-

year population x 1000.

ELEMENTS – Numerator, Denominator,

time & multiplier.

CATEGORIES OF RATE

A)CRUDE RATE- These are the actual observed

rates such as birth and death rates. Crude rates are

also known as unstandardized rates.

B) SPECIFIC RATES –These are actual observed

rates due to :

specific causes(e.g Tuberculosis) or

occuring in specific group(eg. Age, sex groups)

or during specific time period

(eg. Annualy , monthly ,weekly)

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STANDARDIZE RATES-These are

obtained by direct or indirect method of

standardization or adjustment . Eg. Age

and sex standardized rate

RATIO

• Ratio measures the relationship of size of two

random quantities.

• Numerator is not component of denominator.

• Ratio = x / y

Example-

- Sex – Ratio

- Doctor Population Ratio.

PROPORTION

• Proportion is ratio which indicates the

relation in a magnitude of a part of whole.

• The Numerator is always part of

Denominator.

• Usually expressed in percentage.

NUMERATOR AND DENOMINATOR

• Numerator – Number of times an event has

occurred in a population during specified time

period . (sickness, birth)

• Denominator –

1.Total population - Mid-year population -

Population at risk

2. Total events

MEASURING DISEASE FREQUENCY

INCIDENCE AND PREVALENCE

• These are fundamentally different ways of

measuring disease frequency.

• The incidence of disease represents the

rate of occurrence of new cases arising in a

given period in a specified population, while

• prevalence is the number of existing

cases (old+ new) in a defined population at a

given point in time

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INCIDENCE

“Number of new cases occurring in

defined population during specified period

of time”

• Incidence = Number of new cases

during given period / Population at risk x

1000

PREVALENCE

• Prevalence is total no of existing

cases ( old + new) in a defined

population at a particular point in time

or specified period.

• Prevalence = Total no of cases at

given point of time / Estimated

population at specified time x 100

RELATION BETWEEN INCIDENCE &

PREVALENCE

Prevalence = Incidence x Mean duration of d/se.

P = I x D

Example – if, I= 10 cases per 1000 per year.

D = 5 years.

P = 10 x 5

That is 50 cases per 1000 population

1. Point Prevalence

Prevalence for given point of time. •

2. Period Prevalence

Prevalence for specified period.

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SCOPE OF MEASUREMENTS IN

EPIDEMIOLOGY

MEASUREMENTS IN EPIDEMIOLOGY

1. Measurement of mortality.

2. Measurement of morbidity.

3. Measurement of disability.

4. Measurement of natality.

5. Measurement of presence or absence of attributes.

6. Measurement of health care need.

7. Measurement of environmental & other risk

factors.

8. Measurement of demographic variables.