Epidemiology is the study of disease patterns in human populations and the factors that influence health. It involves measuring disease frequency, investigating causes, and controlling health problems. The goals of epidemiology are to understand and reduce the burden of disease in society. Key aspects include describing disease distribution, identifying risk factors, and evaluating interventions. The history of epidemiology began with early physicians like Hippocrates and made advances through pioneers such as John Graunt, William Farr, and John Snow, who conducted seminal studies linking disease to environmental factors. Epidemiology now covers a wide range of fields and plays an important role in public health.

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EpidemiologyEpidemiology

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IntroductionIntroduction
• The term epidemiology is derived from the Greek wordThe term epidemiology is derived from the Greek word
epidemic.epidemic.
– Epi means-Among, upon,Epi means-Among, upon,
– Demos means study population or people andDemos means study population or people and
– Logos means scientific study.Logos means scientific study.
• SoSo
– it is the scientific study of the disease pattern in humanit is the scientific study of the disease pattern in human
population.population.
– In broad sense, it is the study of effects of multiple factors onIn broad sense, it is the study of effects of multiple factors on
human health.human health.
– It is multidisciplinary subject involving those of the physician,It is multidisciplinary subject involving those of the physician,
Biologists, Public Health experts, Health educators etc.Biologists, Public Health experts, Health educators etc.

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DefinitionsDefinitions
• The science of infective diseases, their prime causes,The science of infective diseases, their prime causes,
propagation and prevention. (Stallbrass 1931.)propagation and prevention. (Stallbrass 1931.)
• The science of the mass phenomena of infectiousThe science of the mass phenomena of infectious
diseases or the natural history of infectious diseases.diseases or the natural history of infectious diseases.
(Frost 1927)(Frost 1927)

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DefinitionsDefinitions
• The study of the disease, any diseases, as a massThe study of the disease, any diseases, as a mass
phenomenon. (Greenwood 1935)phenomenon. (Greenwood 1935)
• The study of condition known or reasonably supposedThe study of condition known or reasonably supposed
to influence the prevalence of disease. (Lumsden 1936)to influence the prevalence of disease. (Lumsden 1936)
• Epidemiology as, study of the distribution andEpidemiology as, study of the distribution and
determinants of diseases frequency in man. (Macdeterminants of diseases frequency in man. (Mac
Mohan and Pugh)Mohan and Pugh)

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The widely accepted definition ofThe widely accepted definition of
epidemiology is,epidemiology is,
• ""The study of the distribution and determinantsThe study of the distribution and determinants
of health related states or events in specifiedof health related states or events in specified
population and the application of the study topopulation and the application of the study to
control of health problems“control of health problems“
(J.M. Last 1988)(J.M. Last 1988)

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Basic Tenets of epidemiologyBasic Tenets of epidemiology
• Target of a study in epidemiology is human Population asTarget of a study in epidemiology is human Population as
Geographical area, Age, Sex, Ethnicity, Race etc.: the mostGeographical area, Age, Sex, Ethnicity, Race etc.: the most
common population in epidemiology is the population is acommon population in epidemiology is the population is a
given area or country at a given time. Since the structure ofgiven area or country at a given time. Since the structure of
population varies at each time such variations also have to bepopulation varies at each time such variations also have to be
taken in to consideration during data analysis.taken in to consideration during data analysis.
• All findings must relate to the defined population.All findings must relate to the defined population.
Enumeration is not enough in epidemiology, the population atEnumeration is not enough in epidemiology, the population at
risk of developing that diseases need to be enumerated as well.risk of developing that diseases need to be enumerated as well.

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Basic Tenets of epidemiologyBasic Tenets of epidemiology
• Conclusions are based of comparisons: comparing theConclusions are based of comparisons: comparing the
rates of diseases frequency among the exposed andrates of diseases frequency among the exposed and
unexposed and the unexposed is an importantunexposed and the unexposed is an important
epidemiological method.epidemiological method.
• Description of events by time, place and person.Description of events by time, place and person.
Getting answer for when, where and who are affected isGetting answer for when, where and who are affected is
very important in epidemiology to formulate hypothesisvery important in epidemiology to formulate hypothesis
about its causation. Other important aspects are what,about its causation. Other important aspects are what,
why and how of the events.why and how of the events.

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Aims of EpidemiologyAims of Epidemiology
According to the International Epidemiological AssociationAccording to the International Epidemiological Association
(IEA) Epidemiology has three main aims.(IEA) Epidemiology has three main aims.
– To describe and analyze diseases occurrence and distribution inTo describe and analyze diseases occurrence and distribution in
human populations;human populations;
– To identify etiological factors in the pathogenesis of diseases;To identify etiological factors in the pathogenesis of diseases;
– To provide the data essential to the planning, implementation andTo provide the data essential to the planning, implementation and
evaluation of services for the prevention, control and treatment ofevaluation of services for the prevention, control and treatment of
diseases and to the setting up of priorities among those services.diseases and to the setting up of priorities among those services.

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The ultimate aims of epidemiology can beThe ultimate aims of epidemiology can be
concluded in to two followings points.concluded in to two followings points.
• To eliminate or reduce the health problem or itsTo eliminate or reduce the health problem or its
consequences andconsequences and
• To promote the health and wellbeing of societyTo promote the health and wellbeing of society
as a whole.as a whole.

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Uses of epidemiologyUses of epidemiology
• Investigation of causation of disease.Investigation of causation of disease.
Genetic FactorsGenetic Factors
Good HealthGood Health Ill HealthIll Health
Environmental FactorsEnvironmental Factors

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Uses of epidemiologyUses of epidemiology
• Study of the natural history and prognosis ofStudy of the natural history and prognosis of
diseases.diseases.
Good healthGood health Sub clinical ChangesSub clinical Changes Clinical DiseasesClinical Diseases
DeathDeath
RecoveryRecovery

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Uses of epidemiologyUses of epidemiology
• Description of the health status of theDescription of the health status of the
populations. It includes proportion with illpopulations. It includes proportion with ill
Health, change over time, change with age etc.Health, change over time, change with age etc.
• Evaluation of the interventions.Evaluation of the interventions.
• Planning health services, Public policy andPlanning health services, Public policy and
programs.programs.

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And, RecentlyAnd, Recently
• epidemiologists have become involved inepidemiologists have become involved in
evaluation the effectiveness and efficacy ofevaluation the effectiveness and efficacy of
health services, by determining the appropriatehealth services, by determining the appropriate
length of stay in hospital for specific conditions,length of stay in hospital for specific conditions,
the value of treating High blood pressure, thethe value of treating High blood pressure, the
efficiency of sanitation measures to controlefficiency of sanitation measures to control
diarrhoeal diseases, the impact on public healthdiarrhoeal diseases, the impact on public health
of reducing lead activities in petrol etc.of reducing lead activities in petrol etc.

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Components of epidemiologyComponents of epidemiology
Disease frequency: -Disease frequency: -
• The core characteristics of epidemiology are to measureThe core characteristics of epidemiology are to measure
the frequency of diseases, disability or death in athe frequency of diseases, disability or death in a
specified population. it is always as the rate, ratio andspecified population. it is always as the rate, ratio and
proportion.proportion.
• Much of the subject of epidemiology subject matter ofMuch of the subject of epidemiology subject matter of
measurement of diseases and health related events fallsmeasurement of diseases and health related events falls
in the domain of biostatistics, which is a basic tool ofin the domain of biostatistics, which is a basic tool of
epidemiology. This helps to development of strategiesepidemiology. This helps to development of strategies
for prevention or control of health related problems.for prevention or control of health related problems.

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Components of epidemiologyComponents of epidemiology
Distribution of diseases: -Distribution of diseases: -
• Health events occur in pattern in community and this patternHealth events occur in pattern in community and this pattern
varies from community to community.varies from community to community.
• Also health events or diseases condition affect population atAlso health events or diseases condition affect population at
various age groups, different sexes, different subgroups ofvarious age groups, different sexes, different subgroups of
population.population.
• Distributions of events are based on time, place, and person.Distributions of events are based on time, place, and person.
We can analyze whether any increases or decreases occur for aWe can analyze whether any increases or decreases occur for a
particular condition. Epidemiology addresses itself to a studyparticular condition. Epidemiology addresses itself to a study
of these variations or patterns, which may suggest or lead toof these variations or patterns, which may suggest or lead to
measure to control or prevent the diseases. An importantmeasure to control or prevent the diseases. An important
outcome of this study is formulation of etiological hypothesis.outcome of this study is formulation of etiological hypothesis.

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Components of epidemiologyComponents of epidemiology
Determinants of diseases;Determinants of diseases;--
• Epidemiology helps in identifying the causativeEpidemiology helps in identifying the causative
agent or the risk/predisposing factors ofagent or the risk/predisposing factors of
diseases .diseases .
• This is one of the real uses of epidemiology.This is one of the real uses of epidemiology.
Understanding the factors leading to anyUnderstanding the factors leading to any
programs for the control of those diseases.programs for the control of those diseases.

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History of epidemiologyHistory of epidemiology
• The history of epidemiology has its origin in the idea, goes backThe history of epidemiology has its origin in the idea, goes back
to (400BC) Hippocrates through John Graunt (1662), Williamto (400BC) Hippocrates through John Graunt (1662), William
Farr, John Snow and others that environmental factors canFarr, John Snow and others that environmental factors can
influences the occurrences of diseases in stead of supernaturalinfluences the occurrences of diseases in stead of supernatural
viewpoint of diseases.viewpoint of diseases.
• John Graunt analysis and published the mortality data inJohn Graunt analysis and published the mortality data in
1662.He was the first quantify pattern of death, birth and1662.He was the first quantify pattern of death, birth and
diseases occurances.diseases occurances.
• No one built upon Graunt’s work until 1800’s.when William FarrNo one built upon Graunt’s work until 1800’s.when William Farr
began to systematically collect and analyst the Britain’s mortalitybegan to systematically collect and analyst the Britain’s mortality
statistics. Farr considered as the father of vital statistics andstatistics. Farr considered as the father of vital statistics and
diseases classifications.diseases classifications.

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History of epidemiologyHistory of epidemiology
• Meanwhile John Snow was conducting the series ofMeanwhile John Snow was conducting the series of
investigations in London that later earned him the title father ofinvestigations in London that later earned him the title father of
field epidemiology. Snow conducted his classical study in 1854field epidemiology. Snow conducted his classical study in 1854
when an epidemic of cholera developed in the golden square ofwhen an epidemic of cholera developed in the golden square of
London. During the time of microscope development, snowLondon. During the time of microscope development, snow
conducted studies of cholera outbreak both to discover theconducted studies of cholera outbreak both to discover the
causes of diseases and prevent its recurrences.causes of diseases and prevent its recurrences.
• During that time two men (Farr and snow) had majorDuring that time two men (Farr and snow) had major
disagreement about the cause of cholera. Farr adhere to whatdisagreement about the cause of cholera. Farr adhere to what
was the called miasmatic theory of diseases, according to thiswas the called miasmatic theory of diseases, according to this
theory which was commonly held at a time diseases wastheory which was commonly held at a time diseases was
transmitted by a miasma or cloud that clung low on the earthtransmitted by a miasma or cloud that clung low on the earth
surface.surface.

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History of epidemiologyHistory of epidemiology
• However Snow did not agree he believed that cholera isHowever Snow did not agree he believed that cholera is
transmitted through contaminated water. He began histransmitted through contaminated water. He began his
investigation by determining where in this area personinvestigation by determining where in this area person
with cholera lived and worked. He then used thiswith cholera lived and worked. He then used this
information to map for distribution of diseases. Snowinformation to map for distribution of diseases. Snow
believed that water was the source of infection forbelieved that water was the source of infection for
cholera. He marked the location and searches thecholera. He marked the location and searches the
relationship between cases and water sources. He foundrelationship between cases and water sources. He found
that cholera was transmitted though contaminatedthat cholera was transmitted though contaminated
water. This was the major achievement inwater. This was the major achievement in
epidemiology.epidemiology.

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History of epidemiologyHistory of epidemiology
• In the 1900s epidemiologists extend their methods toIn the 1900s epidemiologists extend their methods to
noninfectious diseases and studied effect of behaviors and lifenoninfectious diseases and studied effect of behaviors and life
style in human health. There are some important achievements instyle in human health. There are some important achievements in
epidemiology they are;epidemiology they are;
– John Snow and cholera epidemic in London in 1848-1854.John Snow and cholera epidemic in London in 1848-1854.
– Framingham heart study started in 1950 in Massachusetts, USA and stillFramingham heart study started in 1950 in Massachusetts, USA and still
continuing to identify the factors leading to the development of thecontinuing to identify the factors leading to the development of the
coronary heart diseases.coronary heart diseases.
– Smoking and lung cancer by Doll and Hill in 1964.Smoking and lung cancer by Doll and Hill in 1964.
– Polio Salk vaccine field trial in 1954 to study the protective efficacy ofPolio Salk vaccine field trial in 1954 to study the protective efficacy of
vaccine in a million school children.vaccine in a million school children.
– Methyl Mercury poisoning 1950s In MinamataMethyl Mercury poisoning 1950s In Minamata

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Field of epidemiologyField of epidemiology
Epidemiology covers the various types of field in differentEpidemiology covers the various types of field in different
types of activities. It is applied in every field as agricultural,types of activities. It is applied in every field as agricultural,
economics, statistics etc. They are aseconomics, statistics etc. They are as
• Clinical epidemiologyClinical epidemiology
• Geographical epidemiologyGeographical epidemiology
• Social epidemiologySocial epidemiology
• Statistical epidemiologyStatistical epidemiology
• Descriptive epidemiologyDescriptive epidemiology
• Analytical epidemiologyAnalytical epidemiology
• Experimental epidemiologyExperimental epidemiology
• Infectious diseases epidemiology etc.Infectious diseases epidemiology etc.

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Comparison between Clinical medicine and Epidemiology
S.
N.
Area Epidemiology Clinical Medicine
1 Unit of study Population ( Defined or at risk) Cases or case
2 objectives To identify the source, Mode of
transmission, etiological factors,
To cure the patient.
3 Examination Group of people or community Individual case
4 Concern with Sick and healthy Sick
5 Diagnosis By survey, research Individual test done.
6 Where to go? Experts goes to community Patient goes to hospital
7 Area concern Mainly concern to preventive and promotive
through intervention
Mainly in curative field
8 Concept Bio-statistical Bio-medical
9 Presentation of
result
By tables, charts and diagrams By laboratory and others reports
10 Time Long process Short time sometimes long time
11 outcome Planning, implementation and health
promotion
Cured or disability or death

23. Concept of disease causationConcept of disease causation
• Germ theory of diseasesGerm theory of diseases
• Epidemiological triadsEpidemiological triads
• Multifactorial causationMultifactorial causation
• Web of causationWeb of causation
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24. Epidemiological triadsEpidemiological triads
• Agent -Agent -Biological, chemical, physical, nutritional, SocialBiological, chemical, physical, nutritional, Social
• Host factor-Host factor- Age, sex, heredity, nutrition, Occupation, Custom,Age, sex, heredity, nutrition, Occupation, Custom,
habits, Immunity power, Biological-Blood sugar, Cholesterol,habits, Immunity power, Biological-Blood sugar, Cholesterol,
Housing, Marital status, socio-economic statusHousing, Marital status, socio-economic status
• Environmental Factor-Environmental Factor- Physical, Biological, PsychosocialPhysical, Biological, Psychosocial
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25. Example – Typhoid FeverExample – Typhoid Fever
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Disease

26. Example – Cervical cancerExample – Cervical cancer
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Disease

27. Dynamic of diseases TransmissionDynamic of diseases Transmission
• Source of Infection or reservoir of infectionSource of Infection or reservoir of infection
• Mode of transmissionMode of transmission
• Susceptible HostSusceptible Host
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28. Reservoir of infectionReservoir of infection
• Human reservoirHuman reservoir
• Case –Case – Clinical, Sub clinical, LatentClinical, Sub clinical, Latent
• Carrier-Carrier- Incubatory, Convalescent, HealthyIncubatory, Convalescent, Healthy
• Animal Reservoir –Animal Reservoir – ZoonoticZoonotic
• Reservoir of nonReservoir of non-- living Things- Soilliving Things- Soil
• Source of Infection- Secretion/ Excretion of reservoirs, Some timesSource of Infection- Secretion/ Excretion of reservoirs, Some times
ReservoirsReservoirs
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29. Mode of Diseases transmissionMode of Diseases transmission
• DirectDirect
• Direct ContactDirect Contact
• Droplet InfectionDroplet Infection
• Inoculation in to skin orInoculation in to skin or
mucosamucosa
• Contact with infectedContact with infected
SoilSoil
• VerticalVertical
• IndirectIndirect
• Vehicle borne diseaseVehicle borne disease
• Vector Borne diseaseVector Borne disease
– BiologicalBiological
– MechanicalMechanical
• Air Borne DiseaseAir Borne Disease
– Droplet NucleiDroplet Nuclei
– Infective DustInfective Dust
• FomiteFomite
• FingersFingers
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30. Susceptible HostSusceptible Host
Low immunity person. High risk personLow immunity person. High risk person
• Portal of entryPortal of entry
 Mode of TransmissionMode of Transmission
• Suitable PlacesSuitable Places
• Develop/ Multiplication/Disease/CarrierDevelop/ Multiplication/Disease/Carrier
• Portal of exitPortal of exit
• RespiratoryRespiratory
• GastrointestinalGastrointestinal
• UrinaryUrinary
• SkinSkin
• Body FluidsBody Fluids07/30/1407/30/14 3030

31. Diseases prevention and controlDiseases prevention and control
• Prevention of source or reservoirPrevention of source or reservoir
• Early diagnosisEarly diagnosis
• NotificationNotification
• Epidemiological InvestigationEpidemiological Investigation
• IsolationIsolation
• TreatmentTreatment
• QuarantineQuarantine
• Interruption of the disease transmissionInterruption of the disease transmission
• Prevention of susceptible hostPrevention of susceptible host
• ImmunizationImmunization
• Health educationHealth education
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32. Epidemiological InvestigationEpidemiological Investigation
• Verification of diagnosisVerification of diagnosis
• Confirmation of the existence of an epidemicConfirmation of the existence of an epidemic
• Defining the population at riskDefining the population at risk
• Obtaining the map of the areaObtaining the map of the area
• Counting the populationCounting the population
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33. ContinueContinue
• Rapid search for all cases and their characteristicsRapid search for all cases and their characteristics
• Medical SurveyMedical Survey
• Epidemiological case sheetEpidemiological case sheet
• Searching for more casesSearching for more cases
• Data analysisData analysis
• TimeTime
• PlacePlace
• PersonPerson
• Formulation of hypothesisFormulation of hypothesis
• Testing of hypothesis Testing of hypothesis
• Evaluation of ecological factors Evaluation of ecological factors
• Further investigation of population at risk Further investigation of population at risk
• Writing the reportWriting the report
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34. study design in Epidemiologystudy design in Epidemiology
• Observational StudyObservational Study
– Descriptive studiesDescriptive studies
– Analytical StudiesAnalytical Studies
• Ecological Study: - Correlation Study unit is a population.Ecological Study: - Correlation Study unit is a population.
• Cross-Sectional Study: - prevalent Study Individual is a unit of study.Cross-Sectional Study: - prevalent Study Individual is a unit of study.
• Case-Control Study: - case-reference with individual is a unit of study.Case-Control Study: - case-reference with individual is a unit of study.
• Cohort study:-Follow up study with individual is a unit of study.Cohort study:-Follow up study with individual is a unit of study.
• Experimental StudiesExperimental Studies
– Randomized Control TrialsRandomized Control Trials
– Field TrialsField Trials
– Community TrialsCommunity Trials
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Thank YouThank You