Basic Concepts in Epidemiology 2

8/11/2019 Basic Concepts in Epidemiology 2

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Basic Concepts in Epidemiology

Agnes Segunda F. Gerasmo M.D. DPAFP


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Topics

I Disease Causation

II Some Useful Concepts in Epidemiology(The Natural History of Disease)

III Ways of Classifying Ill or DisabledPersons


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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.


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Epidemiology

* Etiology- Cause or causes of disease.

* Importance of Causality:1. To understand disease occurrence

and outcome.

2. To identify the links in the chain ofcausality that are amenable to

intervention.


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Definition of Terms

1. Causebrings about effect.

2. Causal Association- a relationship betweencategories of events or characteristics in

which an alteration in the frequency or

quality of one category is followed by a

change in another.


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Definition of terms

3. Statistical Association ( association in the

scientific sense)- the dependence between 2

or more events or characteristic. An

association is present if the probability of

occurrence of an event, depends upon the

occurrence of one or more other variables.


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Steps to determine statistical Relationship


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Statistical Association

1. Positive Association-

occurrence of higher values of one variable isassociated with the occurrence of higher

values of the other.

2. Negative Association-

occurrence of higher values of one variable isassociated with lower values of the other.


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Definition of Terms

Non-causal ( Secondary) statistical Association-

results from the association of both variables

of interest with an extraneous variable.


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Guidelines for Assessing Causal Association

A. Prototype Criteria/ Guidelines

Henle- Kochs Postulates:

1. The organism is always found in the disease in

question.

2. The organism is not found in any other disease.

3. The organism, isolated from one who has the

disease, and cultured through several generationsto produce disease (Animals).


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B. Statistical considerations in

assessing Causation

1. Association and Causation

2 categories of events (exposure and

disease:

1. Statistical Association

2. Non- statistical association

( Not statistically associated)-independent.


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2 Categories

1. Statistically Associated

a. No Casual Association

B. Causal Association

Indirectly AssociatedDirectly Associated


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2 Categories:

2. No statistical association- Independent


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2.2. Defining Variables in Association

1. Independent variables and Dependent

Variables

2. Confounding Variables

3. Intermediate Variables


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Variable

Variablecharacteristic of a person, object or

phenomenon that can take on different

values.

Numerical Variables- the values of these

variables are expressed in number.

Categorical Variables- the values of these

variables in catergories.


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Variables

Independent variable- the variables that areused to describe or measure the factors thatare assumed to cause or at least to influencethe problem.

- the cause

Dependent variables-use to describe or

measure the problem under study.- the effect


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Variable

A study of the relationship between smoking

and lung cancer.

Smoking-independent variable

Lung cancer- dependent variable


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Variable

Confounding variable- a variable that isassociated with the problem and with apossible cause of the problem.

It may either strengthen or weaken theapparent relationship between the problemand the possible cause.

Ex. A STUDY ON LOW LEVEL OF MOTHERSEDUCATION AND MALNUTRITION.


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Variable

Intermediate variable- in between the

independent and dependent variable.


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2.3 Commonly Used Measures of

Association

1. Ratio measures of Association:

a. Rate Ratio

b. Risk Ratio

c. Odds Ratio

2. Difference measures of Association:

a. Rate Differences

b. Risk Differences

c. Attributable Fraction


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Evidence of Causality

A. Experimental Evidence

B. Non-experimental Characteristics


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Non- experimental Characteristics:

1. Temporal Sequence

2. Strength of Association

3. Dose-response to biologic agent

4. Similar Association

5. Plausible

6. Absence of Explanations


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Other Concepts

1. Necessary cause versus Sufficient Cause

2. Risk Factor and Risk Indicator


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II Some Useful Concepts

( The Natural History of Disease)

Natural History of Disease-

the process by which disease occur andprogress in human host.


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Agent

A factor whose presence causes a disease or whose

absence cause disease.

Categories:

Physical, Chemical, Nutrient, Biologic, Genetic and

Psychological agents.

Infectious Agents:

infectivity, pathogenicity, virulence.


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Agents

Non-infectious

Chemical- concentration, toxicity

Physical agents- size, shape, and intensity.Psychological agents- chronicity and

suddenness.

Genetic Agents- homo or heterozygocity.


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Environment

All external conditions and influences affecting

the life of living things.

Physical, Biological and Socioeconomic.

Provides reservoirs where agents can reside orreproduce and modes of transmission.


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Host

The individual human whom an agent produces

disease.

Disease can occur to host that is susceptible.

Lack of susceptibility maybe due:

a. Immunity

b. Inherent Resistance


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Host

Immunitya. Humoral

b. Cellular

a. Passive

B. Active

Inherent Resistance

a. anatomic or physilogic

b. Genetic or Acquiredc. Permanent

d. Temporary


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Relevant Concepts in Disease

Causation

A. Biologic Considerations

Models of disease Causation ( Ecologicmodels:

1. Epidemiologic Triangle


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Models of Disease Causation

2. Epidemiologic Lever and Fulcrum


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Models of Disease Causation

3.Wheel


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Web of Causation


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The Disease Process

2 periods:

1. Prepathogenesis

a. Susceptibility

B. Adaptability

2. Pathogenesis

a. Early disease

b. Early clinical Phase

c. Late clinical Phase


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Natural History of Disease


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Levels of Prevention

1. Primary Prevention

2. Secondary prevention

3. Tertiary Prevention


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Primary Prevention

Aimed at intervening before the pathological changesoccur.

Seeks to keep the agent away from contact with thehost to eliminate or reduce host susceptibility.

Accomplished: General Health Promotion and Specific

Protection.


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Secondary Prevention

to detect disease early, treat promptly and curedisease at its earliest stage.

When cure is not possible to slow progression,prevent complications and limit disability.

Screening the most common form.


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Tertiary Prevention

To limit disability and rehabilitation of persons

for whom residual damage exists.

Activities are focused on the middle to later

phases of disease, when irreversible

pathological damage produces disability.


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Comparison of Prevention for

Infectious and Non-infectious

Prevention of Infectious Dse:

Primary Prevention for communicable dse:

1. Preventing the spread of the infectious agent.

2. Increase host resistance.

Secondary Prevention

1. surveillance program

2. isolation

3. specific treatment


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Comparison of Prevention

Prevention of Non-infectious

Primary Prevention-Agent is destroyed to

prevent the illness to happen or agent is

removed from the environment.

Secondary Prevention-


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Thank You

Basic Concepts in Epidemiology 2

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