introduction to basic epidemiology_jan_2014

8/21/2019 Introduction to Basic Epidemiology_JAN_2014

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DR. M. R. GajendragadPrincipal ScientistNIVEDI , Bengaluru, India.


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ORGANIZATIONOFTHETALK

Introduction

Basic concepts of Epidemiology

Why do we need Epidemiology

Uses of Epidemiology Types of Epidemiological studies


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WHATISDISEASE?

Any impairmentof normal physiologicalfunction affecting all or part of anorganism, especially a specificpathological change caused byinfection, genetic defect, orenvironmental stress, etc., producing

characteristic identifiable group ofsigns or symptoms


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TIME- EPIDEMICCURVES

4


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DISEASESFALLINTOTHREECATEGORIES

1

Endemic diseases of Strategic importance

e.g. Foot and Mouth Disease (FMD)

Chicken pox

2

Diseases requiring tactical attention

e.g. Peste des Petits Ruminants (PPR)

Dengu fever

3

Emerging or evolving diseases

e.g. Bovine spongiform encephalitis (BSE)


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Epidemiology is the study of disease in populationsand of factors that determine its occurrence.

The key word being POPULATION.

Literally, = epi = upon

= demo = people

= logo = discoursing

The study of that which is upon people

The study of disease in populations


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Veterinary epidemiology is the study of disease in animalpopulation

It includes investigation and assessment of other healthrelated events viz., productivity.


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EPIDEMIOLOGICALTRIAD

8

Host

BiologicChemical,

Physical (injury,

trauma)

Stress

Genotype

Nutrition

Immunity

Behaviour

Sanitation

Weather

Pollution

Husbandry

Environment

The disease results from theinteraction between the agent,

(etiology) and the susceptible host(livestock population) in anenvironment that supportstransmission of the agent from asource to the host.

Environmental factors are extrinsicfactors that affect the agent andthe host and the opportunity forexposure.


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EPIDEMIOLOGYISFUNDAMENTALLYABOUT

Population

PlaceOf Disease

Time

Epidemiological analysis & insight results in Identifying and understanding the spatial-temporal

variation in disease


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Why do we need

Epidemiology?


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MANAGINGDISEASERISKS

Multiple perspectives, including:

Food risk Zoonotic risk Trade risk


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WHYDOWENEEDEPIDEMIOLOGY?

To support and sustain:

Basic societal needs

Basic economic needs


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GOODEPIDEMIOLOGYCANHELPSUSTAINBASICSOCIETAL& ECONOMICNEEDS

To live and thrive, we need: Nutritious safe food

Clean water

Public health (therapeutic/diagnostic/preventative)

For economic prosperity, we need: Labour (Healthy work force)

Products (Agricultural trade opportunities - food security:abundance)

Markets (Commercial choice - Food safety: pathogen free)


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HOWDOWESAFEGUARDSOCIETAL& ECONOMICDRIVERS?

We need to understand disease occurrence

Who, what, where, and when of disease, Who = What species/what population

What = What clinical signs/what disease Where = Where is it/what environment factors

When = When has it occurred/seasonal/sporadic

The aim is to understand how and why How = How is it spread/mode of transmission

Why = Why has it occurred now and here

These are the key factors for managing and controllingdisease


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EPIDEMIOLOGY: PROVIDINGEVIDENCEFORPOLICYTOPROTECT& SUPPORTSUSTAINABLEPROSPEROUSSOCIETY

Understanding Who, What, Where, When, How & Why ofdisease occurrence is essential information for: Managing disease events (reactive)

Developing biosecurity & animal husbandry policy (proactive)

Leading to: Better understanding of health & disease status

To help protect: Livelihoods

Livestock production/Trade

To provide: Improved food safety (less zoonotic disease risk)

Sustainable food supply (less livestock risk/food security)


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SKILLSREQUIREDTODOTHISINCLUDEKNOWINGHOWTO:

Observe & record disease events correctly Disentangle the relevant from the irrelevant

Describe distributions

Allowing accurate & valid comparisons

Measureassociations Determine relationships & measure correlations

Provide informed insight Making sense of it all, account for error, variance, bias &

confounding

These arepart of the science & art of epidemiology


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WHYISINTERPRETATIONNEEDED?

In reality, epidemiology is much morethan

finely dressed statistics Kenneth Rothman (2002) Epidemiology an Introduction. Oxford University Press

Epidemiology is the process of building diseasejigsaw puzzles

Puzzles with Lots of pieces

Rarely, if ever, will we find all of the pieces

The pieces are often fuzzy in what they are and how they fit together

Sometimes we put them together incorrectly

The disease picture we are trying to construct can change


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EPIDEMIOLOGICALENQUIRYSTARTSWITHDATA

Data emphasizes evidence

Data collection involves:Outbreak Investigations (Field Epidemiology)

Ongoing Surveillance

Active, Passive, Targeted, Syndromic, Sentinel, Early Warning, Monitoring

Data collection requires appropriate infrastructurePractice,

Evidence based policy


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USESOFEPIDEMIOLOGY

1. Determination of the origin of a diseasewhose cause is known.

2. Investigation & control of a diseasewhose

cause is either unknown or poorly understood.3. Acquisition of information on the ecology andnatural history of a disease.

4. Planning andmonitoring of disease controlprogrammes.

5. Assessment of the economic effectsof adisease & analysis of the costs and economicbenefits of alternative control programme.

6. Monitoring and Riskfactor analysis.


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DETERMINETHEORIGINOFTHEDISEASEWHOSECAUSE IS KNOWN


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INVESTIGATEANDCONTROLOFADISEASEWHOSECAUSEISEITHERUNKNOWN OR POORLYUNDERSTOOD

Epidemiological observations and studies are used toidentify the cause of a disease and there by plan thecontrol strategies

Examples

Protective effect of cowpox virusagainst human small pox.

Feeding of meat and bone meal contamination to cattledeveloped bovine spongiform encephalopathy.


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ACQUISITIONOFINFORMATIONONTHEECOLOGYANDNATURALHISTORYOFADISEASE

Ecosystem

Naturalhistory of

the

diseaseAgent or

the etiologywhich

infects host

Host or the

Animal thatgets infected

Environment influences healthand disease Environmental influences and

disease experience are notconstant in time or uniform inspace

Epidemiology tries todescribe and identify theenvironmental links withdisease occurrence

Disease ecology is about Anthropogenic impacts on

reservoir-host communitiesthat encourage pathogendispersal

In particular cross-speciespathogen dispersal

PLANNING AND MONITORING OF A


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PLANNINGANDMONITORINGOFADISEASECONTROLPROGRAMMES

Disease in an animal population Factors associated withdisease occurrence

Amount of disease

Surveillance & monitoring Costs involved

Benefits gained.

DISEASE CONTROL PROGRAMME


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The Four Most Common Types ofEpidemiological Studies

Cohort StudyThe "What will happen to me?" study follows agroup of healthy people with different levels of exposure andassesses what happens to their health over time.

Case Control StudyThe "why me?" study investigates the prior

exposure of individuals with a particular health condition andthose without it to infer why certain subjects, the "cases,"become ill and others, the "controls," do not.

Occupational Epidemiological StudyThe occupational study canbe designed using any standard epidemiologic design, simplyselecting working people with particular jobs or exposures assubjects.

Cross-Sectional StudyThe "Am I like my neighbors?" studycompares groups in terms of their current health and exposurestatus and assesses their similarities.
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Thanks for your endurance.

introduction to basic epidemiology_jan_2014

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