Lect 1 Intro to Epi

7/27/2019 Lect 1 Intro to Epi

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EPIDEMIOLOGY

Epidemiology


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EPIDEMIOLOGY

EPIDEMIOLOGYThe study of the distribution and determinants of

disease in human populations.

Features:

1. Quantitative science

2. Applied science

3. Uses mostly observational methods4. Systematic and orderly - scientific

5. Focused on populations

Occurrence - Patterns


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EPIDEMIOLOGY

EPIDEMIOLOGY

Epidemiology is the study of the

distribution and determinants of healthrelated states or events in specifiedpopulations and the application of this

study to the control of health problems.

(Last, 1988)


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EPIDEMIOLOGY

2 BROAD CATEGORIES OF

EPIDEMIOLOGY

Descriptive Epidemiology

- study of the amount and distribution ofdisease within a population by person, place andtime

Analytic Epidemiology

-

study of the determinants of disease orreasons for relatively high or low frequency inspecific groups


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EPIDEMIOLOGY

Description of disease patterns /

occurenceDescriptive Epidemiology

Amount and distribution

WHO, WHERE AND WHEN

Amount: Rates and RatiosStandardization of rates

Data gathering and accuracy ofmeasurements

Natural History of Disease


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EPIDEMIOLOGY

Description of disease patterns /

occurenceAnalytic Epidemiology

Etiology, cause, risk factor determinationObservational analytic study types

TESTING DETERMINANTS OF DISEASE


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EPIDEMIOLOGY

IMPORTANTEPIDEMIOLOGICALVARIABLES


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I. CHARACTERISTICS OF PERSONS

(host determinants)

- age

- sex

- ethnic group/ race

- marital status

- occupation

- Socio- economic status

- Family variables:

Size

maternal ageparental deprivationbirth orderinterval between births


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II. CHARACTERISTICS OF

PLACE

- Environmental Factors

- International Comparisons

- Urban Rural Differences


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III. TIME

- Secular Trends- Periodic or Cyclic Fluctuations

- Short Term Fluctuations(Epidemic)


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Methods Utilized in the Study of

Disease Occurrence / PatternsExample:

PTB

Types of Investigations

Describe its featuresand distn. Byanswering:

Find out the reasonsfor the diseaseoccurrence:


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Describe its features and

distn. By answering: WHO is affected

(host factors)- age

- sex

- occupation

- ethnic group

- marital status

WHERE(place factors)

- Geographicaldistn.

WHEN(time factors)

- months- seasonal var.

WHAT- signs and

symptoms- consequences


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WHY

- Reasons

HOW- interplay between different factors of

causation

e.g.

- susceptibility

- source of infection

- vectors

Find out the reasons for thedisease occurrence:


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EPIDEMIOLOGY

HOST DETERMINANTS


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EPIDEMIOLOGY

Most important determinant among the personal

variables In general, chronic conditions tend to increase with age

Young children: readily acquire acute respiratoryinfections

Maternal antibodies transmitted during fetal life protectthe infant for approximately the first half year afterbirth (thereafter, protection wanes and #URTI s)

AGE


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EPIDEMIOLOGY

Measles, chickenpox, mumps occurred mainly in youngchildren; + immunization patterns of immunity in thepopulation changed

Not only related to frequency of infectious disease butalso severity

e.g. Pnuemococcus and salmonellacoliform org./Staph. aureus.

- changing biological influences

- varying behavior

- different experiences

AGE


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EPIDEMIOLOGY

SEX:

Death Rates: Male > Female

Morbidity Rates: Male < Female


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EPIDEMIOLOGY

Reasons:

sex linked inheritance

differences in hormonalbalance

Environment or habit patterns

e.g. > DR in MALE

homicide

COPD

Suicide

Accidents

Liver Disease

heart disease

e.g. > MR in FEMALE

Depression

Attempted suicide

SEX:


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EPIDEMIOLOGY

Reasons for morbidity rate

and mortality rate1. Women seek medical care more freely and perhaps at an

earlier stage of disease

2. That the same disease will tend to have a less lethal coursein women than in men.

- women have more episodes of illness and morephysician contacts than men have

Different habit patterns Physiological differences

Environmental exposures

Sex linked inheritance


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EPIDEMIOLOGY

Many diseases, differ markedly in

frequency, severity, or both in different racialgroups

Many of the observed differences arerelated to differences in socioeconomic status

ETHNIC GROUP OR RACE


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EPIDEMIOLOGY

e.g. Blacks have DR:

- Hypertensive

Heart Disease- CVA

- TB

- Syphilis

- Homicide

- CA of Cervix

Whites have DR:

- Suicide

- Leukemia

- AtheroscleroticHeart Disease

- CA of Breast

ETHNIC GROUP OR RACE


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EPIDEMIOLOGY

OTHER REASONS:Varying environmental exposures, Lifestyles, Extent and quality of

Medical Care

Cultural Differences

Genetic

e.g.

- virtual restriction of sickle cell anemia

to blacks (genetics)- CA of stomach - Japan (native)

- Japanese Desc. in U.S.

- Alcoholism among Jews


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EPIDEMIOLOGY

e.g.

1. CA of Cervix - more common in single with multiple

partners than married women in a monogamy

* Early sexual experience * Infection with HPV

* Multiple partners

2. CA of Breast - more common among single thanmarried women

* Hormonal balance

Risk for breast CA:

- decreased with early age at first pregnancy

- artificial menopause before the age of 40 y/o

OTHER REASONS:


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EPIDEMIOLOGY

Death rates for the SINGLE are

higher than those for the MARRIED1. Persons in poor health tend to remain single.

2. Persons exposed to disease producing agents and

situations tend to remain single.

3. Differences in ways of life of single and married.

GENERALLY, DR for most specific diseases and fromall causes combined, have been found to vary fromlowest to highest in the following order:

Married, Single, Widowed and Divorced.


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EPIDEMIOLOGY

SOCIAL CLASS: Used for ranking or stratifying a total populationinto subgroups that differ from each other in prestige,wealth and power.

- socioeconomic status

- nutritional status

- crowding

- personal hygiene


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EPIDEMIOLOGY

Poverty affects utilization of medical care servicesfor a variety of reasons:

1. Having limited financial resources

2. Restricted access to medical care

3. Poor tend to under utilize available preventive

services

4. Health needs tend to have a relatively lowpriority (lack of motivation to seek suchcare)

SOCIAL CLASS:


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EPIDEMIOLOGY

OCCUPATION:Occupationally related experiences

- can exert a profound effect on health and

contribute to large differences in mortality

e.g.

pulmonary fibrosis - free silica

mesothelioma - asbestos workers

bladder CA - aniline dyes

lung CA - chromate workers


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EPIDEMIOLOGY

Occupational Selection

State of Health may determine entryinto a specific occupation

- undemanding jobs vs demanding jobs

Degree of Stress of the Job

OCCUPATION:


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EPIDEMIOLOGY

PLACE DISEASE

Disease occurrence is

associated withcharacteristics peculiar to

the place of occurrence.


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EPIDEMIOLOGY

PLACE DISEASE

CRITERIA:

1. High rates observed in all ethnic groups

inhabiting the place.2. High rates are not observed among ethnic groups

living in another locality.

3. Migrants develop similar rates as the inhabitants.

4. Reversal of rates if inhabitants leave place.

5. Same manifestations maybe exhibited by otherspecies.


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EPIDEMIOLOGY

TYPES OF COMPARISONS

1. International

2. Urban Rural

3. With Countries

4. Local distribution


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EPIDEMIOLOGY

INTERPRETATION1. Characteristics of inhabitants

2. Characteristics peculiar to place- Biological environment

- Chemical and Physical environment

- Social environmente.g. social conditions determining

preferences, availability and distribution of food malnutrition


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EPIDEMIOLOGY

CHARACTERISTICS OF PLACEPLACE DETERMINANTS

Physical Environment

Chemical Environment

Biologic Environment

Socio cultural Environment


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EPIDEMIOLOGY

MIGRANT STUDIES

Used in delineating theinfluence of geneticinheritance and factorsin the environment


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EPIDEMIOLOGY

MALARIA

0

50

100

150

200

250

YEAR


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EPIDEMIOLOGY

TYPES OF VARIATION INDISEASE FREQUENCY OVER

TIME


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EPIDEMIOLOGY

I. SECULAR CHANGE-Changes in disease frequency encompassinglong periods of time

EXPLANATIONS:

1. Abrupt changes maybe due tovariation in diagnosis, reporting,

coding cause of death

2. Altered killing power of disease

3. Change in the characteristics of thepopulation


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EPIDEMIOLOGY

Forecast of Cancer Deaths

4165

85118

158

211

268311

382

443

510

0

100

200

300

400

500

600

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Years

ThousandsofDeat

hs


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EPIDEMIOLOGY

Cancer Death Rates by SITE


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EPIDEMIOLOGY


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EPIDEMIOLOGY

Possible Reasons for

Changes in Trends Real

Changes in age distribution of the

population Changes in survivorship

Changes in incidence of disease

resulting from Genetic factors

Environmental factors


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EPIDEMIOLOGY

Possible Reasons for Changes

in TrendsArtifactual

Errors in numerator due to

Changes in the recognition of disease Changes in the rules and procedures for

classification of causes of death Changes in the classification code of

causes of death

Changes in accuracy of reporting age atdeath Errors in the denominator due to error in

the enumeration of the population


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EPIDEMIOLOGY

II. CYCLIC FLUCTUATIONS-recurrent alterations in disease frequency

* Seasonal variation

* Every X years cycle - periodicfluctuations on annual or other basis

REASONS FOR VARIATIONS:

1. Differences in peoples activities by season

2. Possible role of insect vectors (influenced bytemp. and humidity for each season)


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EPIDEMIOLOGY

MEASUREMENT OF HEALTH AND

DISEASE IS REQUIRED FOR:

Preventing disease

Promoting healthPlanning health services

THE CENTRAL TOOL OF EPIDEMIOLOGYIS THE COMPARISON OF RATES:

RATE =numerator

denominator


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EPIDEMIOLOGY

Uses of Epidemiology1. Causation

Good Health Ill health

Genetic Factors

Environmental Factors

(Including lifestyle)

Epidemiology can be used to establish CAUSATION; forexample, how genetic and environmental factors can adverselyinfluence people in good health and lead to poor health.


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EPIDEMIOLOGY

Uses of Epidemiology2. Natural History

Good Health SubclinicalChanges

ClinicalDisease

Death

Recovery

Epidemiology can also be used to study the NATURAL HISTORY ofa disease. The person in good health experiences increasing severity ofchange in bodily functions until clinical disease has developed. In the caseof a physical injury these changes usually occur very rapidly. Finally, thedisease or injury may lead to death, or, alternatively, recovery, due to the

bodys natural healing mechanisms or as a result of treatment.


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EPIDEMIOLOGY

Uses of Epidemiology3. Description of health status of populations

Epidemiology can also be used to DESCRIBE the health statusof a population; what proportion is healthy, how health status changesovertime, the occurrence of disease in different geographic areas, etc.

Good

health

ill health

time


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Uses of Epidemiology4. Evaluation of intervention

Good Health

Health promotionPreventive measuresPublic health services

III health

TreatmentMedical care

Finally, epidemiology is increasingly used to EVALUATE theimpact of interventions to prevent disease or injury in a population orthe impact of treatment on groups of patients. In this case,measurements focus on modifications of the ways in which good

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Lect 1 Intro to Epi