Introduction toIntroduction toEpidemiology

Muhammad Tahir, MPH,MSc E&B

Acknowledgments:Yasmin Parpio

Shair Muhammad

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ObjectivesObjectivesBy the end of this session, the students will be y ,

able to:

Define the term “Epidemiology”.p gyState the major objectives of Epidemiology.Discuss the various models employed in the fieldDiscuss the various models employed in the field of EpidemiologyExplain the stages of Natural History ofExplain the stages of Natural History of Diseases.Identify the three levels of prevention.Identify the three levels of prevention.

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Definition of EpidemiologyDefinition of Epidemiology

Epi : UponEpi : UponDemos: PeopleL K l dLogy: Knowledge

It is the study of how disease is distributed in population and of the factors that influencepopulation and of the factors that influence or determine this distribution

(Gordis 1996)(Gordis,1996)

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Definition of EpidemiologyDefinition of Epidemiology

Study of disease and other health-related phenomena in groups of personsphenomena in groups of persons

(Kramer,1990)

“The study of the distribution and determinants ofhealth related states in specified populations andth li ti f thi t d t t l h lththe application of this study to control healthproblems."

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G l / Ai f E id i lGoals / Aims of Epidemiology

Scientific research is the process of suggesting the relationship between cause and disease in a field that may be or not related to public health

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G l / Ai f E id i lGoals / Aims of Epidemiology

Evaluation research is concerned with the decision making process to implement the new strategies, continue the implemented strategies that may be or not in the public health field

To minimize or eradicate the diseaseTo prevent the re-occurrenceTo prevent the re-occurrence

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Uses of EpidemiologyUses of Epidemiology“To provide a clue to changes taking place over ti "time…"

“To identify subgroups in the population who are hi h i k f di "at high risk for disease."

“To determine the best or most appropriate types of primary and secondary prevention.' o Primary prevention prevents disease in the well

i di id l E l i tiindividual. Example: vaccination.

o Secondary prevention limits disease by early detention usually through screening programsdetention usually through screening programs

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Epidemiology & PreventionEpidemiology & Prevention

Why should we identify risk groupsWhy should we identify risk groups

o To identify risk groups and to identify the i t d ifi f t h t i tiassociated specific factors or characteristics

that put them in the risk group.

o Early identification of disease through screening program to prevent the burden of disease on the risk group and to be able to provide the best available intervention

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Specific Objectives of EpidemiologySpecific Objectives of Epidemiology

To identify the causes of disease and the risk f tfactors

To identify the extend of the disease found in the communitycommunity

To determine the health status of population

To study natural history and prognosis of disease

To evaluate new preventive and therapeutic measures and new modes of health care deliverymeasures and new modes of health care delivery.

To provide the foundation for developing public health and regulatory decisions relating tohealth and regulatory decisions relating to environmental problems.

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Components of EpidemiologyComponents of Epidemiology

Identifying both patternDescriptive Epidemiology

Identifying both pattern and frequency of health related events

Focuses on determinantsAnalytical Epidemiology

Focuses on determinants of health outcomes

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Cycle of Epidemiologic AnalysisCycle of Epidemiologic Analysis

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Epidemiological TriadEpidemiological TriadThe cause of any disease whether communicable or non-

communicable are determined by the interactions between the agent, the host and the environment.

Agent

HostEnvironmentAnsari MA,1997

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Epidemiological TriadEpidemiological Triad

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The AgentIs an organism or substance the presence or lackIs an organism or substance, the presence or lack of which may initiate disease process.

Non LivingoNutrients

Classification of AgentoNutrients

Fats, Vitamins, minerals etc.

oChemicalLiving or Biological

Lead, Arsenic, Alcohol etc.

oPhysical

oBacteriaoFungiP t Atmospheric 

pressure, Radiation, Sound, b

oProtozoa oViruses etc.

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Vibrations etc.

Host EnvironmentThe Host is the man himself and his

Acts as a reservoir for the agents ofhimself and his 

characteristics. e.g. age, sex, and race (ethnicity) socio

for  the agents of disease.

(ethnicity) socio economic status, life style.

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The Host ‐ Environment Interaction

“Virtually all chronic diseases have multi‐factorialetiologies” many may have infectious components

Enteroviruses Type I diabetes

etiologies  ‐‐many may have infectious components.

ypEpstein Barr virus B-cell lymphomasChlamydia pneumoniae Heart diseaseChlamydia pneumoniae Heart diseaseHelicobacter pylori Peptic ulcersHepatitis B and C Liver cancerBorna disease virus Schizophreniap

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Wheel ModelWheel Model

Wheel model is another approach to depicting h i t l tihuman environment relations.

o Definition: The wheel consists of a hub thatrepresents the host with all of its humancharacteristics such as genetic make up,personality and immunity The surrounding wheelpersonality, and immunity. The surrounding wheelrepresents the environment and comprises ofbiological, social and physical dimensions.g , p y

o The relative size of each component in the wheel depends on the health problem being analyzed.depends on the health problem being analyzed.

(Mary To Clark, 1992)

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Wheel Model

Genetic core

18Mausner, J. S. & A. K. Bahn. 1974. Epidemiology. Sanders, Philadelphia.

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ClassificationClassification

Physical: Is the space around man containingPhysical: Is the space around man containing gases (air) liquids (water) and solids.

Biological: All living things that surrounds man. Both animals and plants.p

Social: The customs habits culture educationSocial:  The customs, habits, culture, education and the living standards.

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The Web Of CausationThe Web Of Causation

The web of causation views a health condition not ao The web of causation views a health condition not athe result of individual factors, but of complexinterrelations among multiple factors i.e. one factormay lead to others which in turn lead to others all ofmay lead to others, which in-turn lead to others, all ofwhich may interact with one another to produce thehealth condition.

Features:

o It also includes environment, host, and agent factors. , , g

o It allows for interaction between different components.

o It suits chronic diseases and environmental effectso It suits chronic diseases and environmental effects.

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Web Of Causation

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Phases of EpidemiologyPhases of Epidemiology

Descriptive Epidemiology:o It is concerned with disease distribution and

frequency. It asks: what is the problem its f h i i l d Wh d hfrequency, who is involved. Where and when.

l l lAnalytical Epidemiology: 

o Attempts to analyze the causes or determinants of diseases by testingdeterminants of diseases by testing hypotheses. By asking how and why questions.questions.

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Phases of EpidemiologyPhases of Epidemiology

E perimental EpidemiologExperimental Epidemiology:Used to answer questions about the ff ti f th d f t llieffectiveness of new methods for controlling

disease or for improving under lying conditionsconditions.

Evaluation Epidemiology:Evaluation Epidemiology:It attempts to measure the effectiveness of different health services and programsdifferent health services and programs.

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Epidemiological ApproachEpidemiological Approach

The information required can be approached through a series of questions.

What Is the health program/disease?Wh I ff t d d i l l ?Who Is affected age, sex, and social class?Where Does the problem occur?When I t f d th d ?When In terms of days, months, seasons, and years?How Health Problem occurs, specific causative agent?

Why Does it occur reasons for its occurrence?Why Does it occur, reasons for its occurrence?

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Series of QuestionsWhat is the health problem?

Who is affected with reference to age sex social class ethnic groupWho is affected, with reference to age, sex, social class, ethnic group, occupation, heredity and personal habits?

Where does the problem occur, in relation to place of residence, hi l di t ib ti d l f ?geographical distribution and place of exposure?

When does it happen, in terms of day, months, seasons or years?How does the health problem or disease occur?How does the health problem or disease occur?

Why does it occur, in terms of the reasons for its persistence or occurrence?

What interventions have been implemented as a result of the information gained and what was their effectiveness?

Have there been any improvements in health status?26

Natural History of DiseaseOnset of Usual time of

Exposure

Pathologic

Onset ofsymptoms

Usual time of diagnosis

Pathologicchanges

Stage ofsusceptibility

Stage ofsubclinical

disease

Stage of clinical disease

Stage of recovery,

disability ordisease disability or death

Primary Prevention Secondary

Prevention Tertiary P ti

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Prevention

The Natural History of DiseaseThe Natural History of Disease

Stage 1: SusceptibilityStage 1: Susceptibility

Description: Ri k f t hi h i tDescription: Risk factors which assist the development of disease exist, but diseasedisease exist, but disease has not developed

Example: Smoking

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The Natural History of Disease(cont’d)

St 2Stage 2: Pre-symptomatic disease

Description: Changes have occurred to lead toward illness but disease is not yetdisease is not yet clinically detectable

Example: Alveoli deteriorate

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The Natural History of Disease(cont’d)

Stage 3: Clinical Disease

Description: Detectable signs and/or t f di i tsymptoms of disease exist

Example: Emphysema detected by pulmonary function test

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The Natural History of Disease(Cont’d)

Stage 4: DisabilityStage 4: Disability

Description: Di h dDescription: Disease has progressed to the point of causing a residual effect

Example: Person has difficulty p ybreathing

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Levels of PreventionLevel: Primary

Description: Promote general healthDescription: Promote general healthand avoid risk factors fordisease --- Utilize protective pmeasures to prevent susceptibility and pre-symptomatic diseasepre symptomatic disease

Example: Stop smoking or chooseExample: Stop smoking or choose not to start; avoid areas where people are smoking

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Levels of Prevention(Cont’d)

Level: SecondaryDescription: Early detection and

timely treatmentExample: Routine pulmonary

function tests for those at risk; medicine to help patients breath more easily; smoking cessationeasily; smoking cessation programs if patient smokes

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Levels Of Prevention(cont’d)

Level: Tertiary

Description: Rehabilitation and prevention of further pdisease or disability

Example: Oxygen therapy; facilitating ambulation gwith technical devices

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Prevention Approachespp

Population‐Based Approach:

Preventive measure widely applied to an entire population (public health approach)p p (p pp )

Strive for small absolute change amongStrive for small absolute change among many persons

Must be relatively inexpensive and non-invasive

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Prevention Approachespp

High‐Risk Approach:

Target group of individual at high risk

Strive for strong risk factor control

Often times requires clinical action to identify the high risk group and to motivateidentify the high risk group and to motivate risk factor control.

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L l f P tiLevels of Prevention 

Primary Prevention

Prevention of disease by controllingPrevention of disease by controlling risk factors (e.g., non-smoking

promotion)

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Levels of PreventionLevels of Prevention 

S d P tiSecondary Prevention

Reduction in consequences of disease byReduction in consequences of disease by early diagnosis and treatment

(e.g., cervical cancer screening)

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Levels of Prevention 

Tertiary PreventionTertiary Prevention

Reduction in complications of diseaseReduction in complications of disease(e.g., MV crashes and ICU)

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Group AssignmentGroup Assignment

Group 1 : Epidemiological Triad for Scabies

Group 2: Wheel Model for Drug addiction e g C biGroup 2: Wheel Model for Drug addiction e.g. Cannabis

Group 3: Web of Causation of Malnutrition

Group 4: Natural History of Hypertension

Group 5: Level of Prevention for IHD [Ischemic heart Disease]

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