Definition of Health - University of...

Lesson 3: Epidemiology April 11, 2006

ENV H 311: Intro. to Environmental

Health 1

ENV H 311: Lesson 3 1

Lesson 3. Epidemiology

Human Disease:

Identification &

Control Strategies

Chuck TreserChuck TreserUniversity of WashingtonUniversity of Washington

Dept. of Environmental andDept. of Environmental and

Occupational Health SciencesOccupational Health Sciences

April 11, 2006April 11, 2006


Definition of Health

“Health is the state of completephysical, mental and social wellbeing and not merely the absence ofdisease or infirmity.”

World Health Organization1970


EnvironmentalExposures

IntrinsicGenetic

Susceptibility

Age / Time

Determinants of Health



Health 2


“Genetics loads the gun . . .

but the environment pulls thetrigger.”

Dr. Judith Senn

Professor of Nutrition & Internal MedicineUniv. Of California, Davis


HostAgent

Environment

Disease Causation


Disease Causation

HostAgent

Environment



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Disease & Injury

Acute Effects

Infectious Diseases

Injuries

Chronic Effects

Chronic Disease

Disability


Environment

Agent Host

Epidemiological Model


Origins

John Snow(1813-1858)

John Snow's original 1854 map on the location of 578 deaths from Cholera, from An Introduction to VisualisationSoftware for Astronomy, Starlink Guide 8.1, A C Davenhall, 9th February 1996 CCLRC / Rutherford Appleton

Laboratory Particle Physics & Astronomy Research Council



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Epidemiology

Looks for patterns of diseaseoccurrence

Geographically

Demographically


Definition

Epidemiology is the study of

the distribution and

determinants of

health effects (disease & injuries)

in human populations


Distribution Factors

Person

Place

Time



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PersonAge

Race

Sex

Occupation

Education

Hobbies


Population Differences



Person

Age

Race

Sex

Time

Episodic

Cyclical

Secular



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Temporal Distribution



Person

Age

Race

Sex

Time

Episodic

Cyclical

Secular

Place

Geographic

Longitude &

Latitude

Geologic

Climatic

Geo-political

Urban / Rural

Industry

Pollution


Spatial Distribution



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Determinants

Determinants

Agent

Host

Environment


Determinants

Agent Factors

Biological

Chemical

Physical

Host Factors

GeneticPredisposition

Exposure

EnvironmentFactors

NaturalEnvironment

Built Environment

Socio-culturalEnvironment

TemporalEnvironment


Balance BeamAffects equilibrium through:1. Interaction with agents2. Individual habits & group customs3. Age, sex & race characteristics4. Defense Mechanisms5. Constitution and heredity6. Psychologic characterisitics

Changes upset balance

Human Host

Affect equilibrium through:1. Their basic nature and character2. Resistance and lability3. Reservoir and Sources4. Conditions of dissemination

These determine the balance of health and

preventive attack

Disease AgentsParasitic, Nutrient, Chemical,

Physical & Mechanical

Environment

PhysicalBiological

Economic &Social-Political

At Equilibrium

Variable fulcrum position

Variable fulcrum position

Simplified diagram of factors influencing equilibrium. Adapted from Leavell HR and Clark EG. Preventive Medicine for the Doctor in his Community.



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The Disease Process

Natural History of Disease

Problems with Detection & Reporting


DEATH

Chronic

Defect

Disability

Illness

Signs &Symptoms

Tissue &Physiologic Changes

STIMULUS or AGENTbecomes established and increases by multi- plication or incrementIn the

HumanHost

Clinical Horizon

The course of disease in man

RECOVERY

EarlyPathogenesis

DiscernableEarly

Lesions

AdvancedDisease

Convalescence

THE NATURAL HISTORY OF ANY DISEASE IN MAN

Prepathogenesis Period Period of Pathogenesis

Interaction ofHOST & STIMULUS HOST

REACTION

Adapted from: Leavell, Hugh R. and E. Gurney Clark, Preventive Medicine for the Doctor in His Community .

Before man isinvolved

Interrelationship of the various

AGENT / HOST / ENVIRONMENTFactors

(Known and Unknown)

Whichwhich bring together the

AGENT and HOST

Or

Produce a disease producing

STMULUS

ENV H 311: Lesson 3 24Infection terminated,

become latent or intermittently patent

Disease in host

Agent being shed

Total period of infection (agent present)

InfectionLatent

Latentperiod Period of

communicability

Infectionpatent

m: Fox, Hall, Elveback. Epidemiology: Man and Disease, The Macmillan Company, 1970:57.

Schematic Diagram of the Stages of Infection in a Host

Incubationperiod



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THE NATURAL HISTORY OF ANY DISEASE IN MAN

LEVELS OF APPLICATION OF PREVENTIVE MEASURESPrimary Prevention Secondary Prevention Tertiary Prevention

Period of PathogenesisPrepathogenesis Period

HEALTH PROMOTION

Use of specific immunizations

Attention to personal hygiene

Use of environmental sanitation

Protection against occupational hazards

Protection from accidents

Use of specific nutrients

Protection from carcinogens

Avoidance of allergens

Health Education

Good standard of nutritionadjusted to the develop-mental phase of life

Attention to personalitydevelopment

Provision of adequatehousing, recreationand agreeable workingconditions

Marriage Counseling and sex education

Genetics

Periodic selective examinations

Case-finding measures,individual and mass

Screening surveys

Selective examinations

Objectives• To cure and prevent disease processes• To prevent the spread of communicable disease• To prevent complications and sequelae• To shorten the period of disbility

Adequate treatment toarrest the diseaseprocess and to preventcomplications and sequelae

Provision of facilities tolimit disability and toprevent death

Provision of hospital andcommunity facilities forretraining and educationfor maximum use of re-maining capacities

Education of the publicand industry to utilizethe rehabilitated

As full employment aspossible

Selective placement worktherapy in hospitals

Interrelations of Agent, Host andEnvironment Factors

Production of STIMULUS

Reaction of the HOST to the STIMULUS

Early Pathogenesis

DiscernableEarly Lesions

AdvancedDisease

Conva-lescence

SPECIFIC PROTECTIONEARLY DIAGNOSIS &PROMPT TREATMENT DISABILITY

LIMITATIONS REHABILITATION


Contingencies of Morbidity Reporting

Symptoms? Complaints?• Stoical• Ashamed

ConsultationSought?• Lack of funds• Indifference• "Don't believe in doctors"

DiagnosisSuspected?• MD's acumen• Nature of Complaint• Communication• Rarity of disease

DiagnosisEstablished?• Too early• Too late• Follow up

Report Made?• Ignorance• Indifference• Forgot• Rarity of disease

POPULATION

No

Yes

No

Yes

No

Yes

No

Yes

No

Yes

No

Yes


Concepts & Methods

Disease Prevalence – the proportionof a population with the disease, at achosen point in time. (snap shot)

Rp = CT / P (x 100,000)(at that time)

E.g., 10% of the population of KingCounty has respiratory asthma atpresent.



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Prevalence Rate


Prevalence Rate


Concepts & Methods Continued

Incidence Rate – the proportion of apopulation with newly-diagnoseddisease per given unit of time.(New cases over time)

Ri = Cn / P (x 100,000)(at the midpoint of the unit of time)

E.g., the total mortality rate (alldeaths) is 0.89% per year among thepopulation of Seattle



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Incidence Rates

That is, in a given year there were 4450deaths reported among residents ofSeattle, a population of 500,000.

Incidence rate = 4450 / (500,000 x 1year) = 0.0089/year

= 890 per 100,000 persons per year

= 2.4 per 100,000 persons per day


Incidence Rate


Analytic Techniques

Stratification – dividing the sampleaccording to some characteristic,e.g. age:

Age-specific deaths from heart disease among non-smokingBritish male doctors

Age Deaths/104 persons per year

35-44 1.064

45-54 11.23

55-64 49.04

65-74 96.71

75-84 212.04

Total 25.75



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Analytic Techniques Continued

Association of disease with anenvironmental factor – comparingdisease prevalence or incident ratesbetween groups with and withoutexposure to the environmental factor



Age-specific deaths from heartdisease among smoking British maledoctors.

Relative RiskAge Deaths/104 persons per year (RR)

35-44 6.106 5.74

45-54 24.05 2.14

55-64 72.00 1.47

65-74 146.88 1.52

75-84 191.84 0.91

Total 44.29 1.72



What if smoking British male doctorsdrink more ethanol, compared tonon-smoking British male doctors?Since from other studies we knowthat ethanol is associated with heartdisease, can we argue that smoking isthe cause of heart disease mortalityin this group?



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Confounding factor: a factor that isassociated both with exposure andoutcome, and thus interferes indetermining the relationshipbetween exposure and outcome.Ethanol in this case is a confounder


Limitations

Most environmental diseases havemultiple contributing causes – e.g. lungcancer, heart disease – so multipleexposures must be measured.

Smoking, age, diet, and genetic make-up are powerful interfering factors


Limitations Continued

Measurement of exposure can behighly inaccurate, especially whenpast exposures are needed. Theusual result is called misclassifica-tion, and any underlying associationbetween exposure and illness islikely to be missed or underesti-mated



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Latency of many (most?) environmentaldiseases is years to decades.

Thus exposures from the distant past aremost relevant, and least likely to be knownquantitatively.

Longitudinal epidemiology, in whichexposed persons are followed overyears, is most precise.



Examples of longitudinal studies:

Framingham, Mass. heart disease;

Fluoridation of water and dental caries;

Salk vaccine and polio incidence;

Smoking and several diseases.



An observed association betweenenvironmental agent and disease shouldnot be termed a cause-effect relation-ship until a biological mechanism hasalso been demonstrated.

Otherwise, the observed epidemiologicoutcome could easily be a coincidence.



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HostAgent

Environment

Disease Causation


Disease Causation

HostAgent

Environment


HostAgent

Environment

Disease Control



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Prevention & Control

Modify the environment

Engineering Controls

Modify Behavior

Legal/Regulatory Controls

Administrative Controls

Education


Engineering Controls Tactics

Substitution

Treatment

Isolation

Shielding


Control Tactics Continued

HostAgent

Substitution

Newcompound or

process



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HostAgent

Treatment



HostAgent

Isolation



Host

Shielding

Agent



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Regulatory Controls

Statutes

Rules and Regulations

Enforcement Programs

Private Sector Control



Planning

Supervision

Biological Monitoring

Work Scheduling


Education

Education

Training

Safety campaigns

Administrative priority



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Control Strategies Continued

In order of effectiveness

Engineering Control Tactics

Legal / Regulatory Controls


Education

How do we operationalize these?


Summary

Epidemiology is the study of thedistribution and determinants ofhealth effects in human populations

Distribution

Person

Place

Time

Determinants

Agent

Host

Environment


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