FMS, UWI, Cave HillFMS, UWI, Cave HillHEALTH CARE HEALTH CARE CONCEPTS:CONCEPTS:

Lecture 2. Natural History Lecture 2. Natural History of Disease / Approaches to of Disease / Approaches to Disease Prevention Disease Prevention

Alafia Samuels MBBS, MPH, PhDAlafia Samuels MBBS, MPH, PhDSenior Lecturer, Epidemiology & Public HealthSenior Lecturer, Epidemiology & Public HealthFaculty of Medical Sciences, UWI, Cave HillFaculty of Medical Sciences, UWI, Cave Hill

Email: alafia.samuels@cavehill.uwi.eduEmail: alafia.samuels@cavehill.uwi.edu

Main ReferencesMain References

An Introduction to Public Health An Introduction to Public Health and Epidemiologyand Epidemiology

Susan Carr, Susan Carr, Nigel Unwin, , Tanja Pless-Mulloli

(University of Northumbria, University of (University of Northumbria, University of Newcastle upon Tyne, University of Newcastle)Newcastle upon Tyne, University of Newcastle)

Open University Press, McGraw Hill EducationOpen University Press, McGraw Hill Education

Basic EpidemiologyBasic EpidemiologyR. Bonia, R. Beaglehole, T. KjellstromR. Bonia, R. Beaglehole, T. Kjellstrom

World Health OrganizationWorld Health Organization

Learning ObjectivesLearning Objectives

To describe and explain the To describe and explain the natural history of disease natural history of disease

To appraise the relationship To appraise the relationship between natural history of between natural history of disease and levels of preventiondisease and levels of prevention

To compare primary, secondary To compare primary, secondary and tertiary preventionand tertiary prevention

USA Healthiest nationUSA Healthiest nation

Global Causes of DeathGlobal Causes of Death

CNCDCNCD = 60% = 60%

INJURIES = 10%INJURIES = 10%

COMM / MCH = 30%COMM / MCH = 30%

Cardiovascular disease, Cardiovascular disease, mainly heart disease, mainly heart disease, strokestroke

DiabetesDiabetes CancerCancer Chronic respiratory Chronic respiratory

diseases (asthma)diseases (asthma)

"Leading infectious causes of cancer, 2000" from Public Health "Leading infectious causes of cancer, 2000" from Public Health Biology. Available at: Biology. Available at: http://ocw.jhsph.edu. Copyright © Johns Hopkins . Copyright © Johns Hopkins

Bloomberg School of Public Health. Creative Commons BY-NC-SA.Bloomberg School of Public Health. Creative Commons BY-NC-SA.

Schematic representation of the natural Schematic representation of the natural history of diseasehistory of disease

CAB

E

D

OUTCOMES: Death

Chronicity

Residual DisabilityInapparent or

Subclinical

Disease

Clinical Disease

Clinical Horizon

Cure

STAGES OF DISEASE

No Disease No Overt Symptoms

SymptomaticDisease

Resolution

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Degrees of disability e.g. Degrees of disability e.g. diabetesdiabetes

Impairment Impairment – Any loss of structure or function: Any loss of structure or function:

eventual pancreas burn-out, reduced eventual pancreas burn-out, reduced ability to secrete insulinability to secrete insulin

Disability Disability – Any restriction in ability to do activities Any restriction in ability to do activities

normal for the human being: lower normal for the human being: lower extremity amputation (BK or AK)extremity amputation (BK or AK)

Handicap Handicap – Disadvantage that limits the fulfillment Disadvantage that limits the fulfillment

of the individual’s normal role in the of the individual’s normal role in the community: amputation and no community: amputation and no wheelchairwheelchairDr. Rasha Salama, PhD. Community Medicine, Suez Canal University, Egypt

Schematic representation of the natural Schematic representation of the natural history of disease – Tissue changeshistory of disease – Tissue changes

CAB

E

D

OUTCOMES: Death

Chronicity

Residual DisabilityInapparent or

Subclinical

Disease

Clinical Disease

Clinical Horizon

Cure

STAGES OF DISEASE

SUSCEPTIBILITY PATHOGENESISTISSUECHANGES

No Disease No Overt Symptoms

SymptomaticDisease

Resolution

Schematic representation of the natural Schematic representation of the natural history of disease – Levels of preventionhistory of disease – Levels of prevention

CAB

E

D

OUTCOMES: Death

Chronicity

Residual DisabilityInapparent or

Subclinical

Disease

Clinical Disease

Clinical Horizon

Cure

STAGES OF DISEASE

SUSCEPTIBILITY PATHOGENESISTISSUECHANGES

LEVEL OFPREVENTION

PRIMARYPREVENTION

SECONDARY PREVENTION

TERTIARYPREVENTION

Schematic representation of the natural Schematic representation of the natural history of disease – Modes of interventionhistory of disease – Modes of intervention

CAB

E

D

OUTCOMES: Death

Chronicity

Residual DisabilityInapparent or

Subclinical

Disease

Clinical Disease

Clinical Horizon

Cure

STAGES OF DISEASE

SUSCEPTIBILITY PATHOGENESISTISSUECHANGES

LEVEL OFPREVENTION

PRIMARYPREVENTION

SECONDARY PREVENTION

TERTIARYPREVENTION

MODES OF Health Promotion Screening Treatment and INTERVENTION Specific Early Detection Limitation of Disability / Rehabilitation

Protection Prompt treatment Chronic Care

Healthy PublicPolicies

•Social Class•Gender•Ethnicity

•Place•Housing•Occupational Risks•Access to services

•Smoking•Nutrition•Physical Activity•Psicosocial Factors

•Blood Pressure•Cholesterol•Obesity

Coronary HeartDisease

CommunityInterventions

Primary &SecondaryPrevention

SecondaryPrevention

SocialDeterminants

EnvironmentalInfluences

Life Styles

PhysiologicalFactors

Social determinants of health in Latin America and the Caribbean

From McKinlay and Marceau, A tale of 3 tails Am J Public Health 1999 89: 295-298.  

13

Prevention: Why?Prevention: Why?

Preventing is better than Preventing is better than treatmenttreatment– Prevention Prevention maintains maintains health – health –

treatment treatment restoresrestores– Prevention can be possible when Prevention can be possible when

treatment is nottreatment is not– Prevention is more cost-effective…..Prevention is more cost-effective…..

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Prevention is Prevention is sometimes cheaper sometimes cheaper than cure….than cure….

Immunisation is definitely cheaper than treating MMR, DPT, OPV (measles, mumps rubella, diptheria, pertussis, tetanus, polio)

Treating hypertension is cost - saving Other preventions are often expensive Competitive mortality

– may live longer and get more expensive disease

Public Health Canada Public Health Canada ROIROI

16

Prevention can be Prevention can be difficultdifficult

Alcohol-related problems are not likely Alcohol-related problems are not likely to be reduced by strategies involving to be reduced by strategies involving single interventions directed solely at single interventions directed solely at the individual;the individual;

Economic, political, social and Economic, political, social and environmental forces that perpetuate environmental forces that perpetuate these problems must also be addressedthese problems must also be addressed

NIAAA, AHRW, Vol. 17, No. 2, 1993, p. 133NIAAA, AHRW, Vol. 17, No. 2, 1993, p. 133

The natural history of diseaseThe natural history of disease

STAGE 1:STAGE 1: SusceptibilitySusceptibility

DESCRIPTION:DESCRIPTION: Risk factors which assist Risk factors which assist the development of the development of

disease exist, but disease exist, but disease disease has not has not developeddeveloped

EXAMPLE:EXAMPLE: SmokingSmoking

LEVELS OF LEVELS OF PREVENTIONPREVENTION

LEVEL:LEVEL: PrimaryPrimary

DESCRIPTION:DESCRIPTION: Promote general healthPromote general health

and avoid risk factors forand avoid risk factors for

disease --- Utilize protective disease --- Utilize protective measures to prevent measures to prevent

susceptibility and susceptibility and presymptomatic disease presymptomatic disease

EXAMPLE:EXAMPLE: Stop smoking or choose Stop smoking or choose not to start; avoid areas not to start; avoid areas

where people are smoking where people are smoking

Countries don’t have Countries don’t have to be rich in order to to be rich in order to be healthy.be healthy.

Given today’s tools Given today’s tools and resources, much and resources, much better health should better health should and can be the normand can be the norm—in countries rich —in countries rich and poor alike.and poor alike.

Stopping smoking works

Source: Peto et al, 2000

Which interventions are Which interventions are effective?effective?Measures to reduce demandMeasures to reduce demand

Higher cigarette taxesHigher cigarette taxes Non-price measures: advertising and Non-price measures: advertising and

promotion bans, consumer promotion bans, consumer information, warning labels and information, warning labels and restrictions on public smokingrestrictions on public smoking

Increased access to nicotine Increased access to nicotine replacement (NRT) and other replacement (NRT) and other cessation therapiescessation therapies

Source: Jha et al, 2006, DCP2.org

Cigarette price and consumption show Cigarette price and consumption show opposite trends (2)opposite trends (2)Real price of cigarettes and consumption in Real price of cigarettes and consumption in South Africa, 1960-2003South Africa, 1960-2003

Source: Van Welbeck 2003

0

200

400

600

800

100019

60

1964

1968

1972

1976

1980

1984

1988

1992

1996

2000

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pac

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)

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500

1000

1500

2000

2500

Cig

aret

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sum

pti

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(m

illi

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)

Real price of cigarettes Consumption of cigarettes

The natural history of diseaseThe natural history of disease (cont’d) (cont’d)

STAGE 2:STAGE 2: Presymptomatic diseasePresymptomatic disease

DESCRIPTION:DESCRIPTION: Changes have occurred Changes have occurred to lead toward illness but to lead toward illness but disease is not yet disease is not yet

clinically clinically detectabledetectable

EXAMPLE:EXAMPLE: Alveoli deteriorateAlveoli deteriorate

LEVELS OF PREVENTIONLEVELS OF PREVENTION (cont’d) (cont’d)

LEVEL:LEVEL: SecondarySecondary

DESCRIPTION:DESCRIPTION: Early detection and Early detection and timely treatment timely treatment

EXAMPLE:EXAMPLE: SCREENING SCREENING

Pap smear, mammogram, Pap smear, mammogram, ?PSA, blood glucose, ?PSA, blood glucose, cholesterolcholesterol

SCREENING e.g. SCREENING e.g. MONITORING BLOOD MONITORING BLOOD PRESSURE in the PRESSURE in the communitycommunity

The Washington PostThe Washington PostFriday, November 16, 2007Friday, November 16, 2007

Clipping Away at IllnessBarbers and Salons Catering to Blacks

Add Health Checks to List of Services

The natural history of diseaseThe natural history of disease (cont’d) (cont’d)

STAGE 3:STAGE 3: Clinical DiseaseClinical Disease

DESCRIPTION:DESCRIPTION: Detectable signs and/or Detectable signs and/or symptoms of disease existsymptoms of disease exist

EXAMPLE:EXAMPLE: Emphysema detected by Emphysema detected by pulmonary function test pulmonary function test

The natural history of diseaseThe natural history of disease (cont’d) (cont’d)

STAGE 4:STAGE 4: DisabilityDisability

DESCRIPTION:DESCRIPTION: Disease has progressed to Disease has progressed to the point of causing a the point of causing a

residual effectresidual effect

EXAMPLE:EXAMPLE: Person has difficulty Person has difficulty breathing breathing

LEVELS OF PREVENTIONLEVELS OF PREVENTION (cont’d) (cont’d)

LEVEL:LEVEL: TertiaryTertiary

DESCRIPTION:DESCRIPTION: Rehabilitation and Rehabilitation and prevention of further prevention of further

disease or disabilitydisease or disability

EXAMPLE:EXAMPLE: Oxygen therapy; Oxygen therapy; facilitating ambulation facilitating ambulation with technical deviceswith technical devices

Finland: Dramatic Declines in Finland: Dramatic Declines in NCD MortalityNCD Mortality

Finland: Cardiovascular Finland: Cardiovascular risk factorsrisk factors

Majority (about 75%) of decline in Majority (about 75%) of decline in heart heart diseasedisease mortality due to mortality due to reductions in three risk factorsreductions in three risk factors: :

– Blood pressure Blood pressure – CholesterolCholesterol– Smoking Smoking

Vaartiainen, E, Puska P, Pekkanen J, Tuomilheto J, Jousilahti P. Do changes in risk factors in Vaartiainen, E, Puska P, Pekkanen J, Tuomilheto J, Jousilahti P. Do changes in risk factors in Finland explain the changes in ischemic heart Finland explain the changes in ischemic heart diseasedisease mortality? In: Puska P, mortality? In: Puska P, Tuomilehto J, Nissinen A, Vartiainen E (eds). Tuomilehto J, Nissinen A, Vartiainen E (eds). The North Karelia Project: 20 Year Results The North Karelia Project: 20 Year Results

and Experiencesand Experiences. Helsinki: National Public Health Institute, 195, pp.241–54.. Helsinki: National Public Health Institute, 195, pp.241–54.

PREVENTION PREVENTION APPROACHESAPPROACHES

Population-Based ApproachPopulation-Based Approach::•• Preventive measure widely applied to Preventive measure widely applied to

an entire population (public health an entire population (public health approach)approach)

•• Strive for small absolute change Strive for small absolute change among many personsamong many persons

•• Must be relatively inexpensive and Must be relatively inexpensive and non-invasivenon-invasive

PREVENTION PREVENTION APPROACHESAPPROACHES

High-Risk ApproachHigh-Risk Approach::

•• Target group of individual at high riskTarget group of individual at high risk

•• Strive for strong risk factor controlStrive for strong risk factor control

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

Youtube: Primary Youtube: Primary Secondary Tertiary Secondary Tertiary prevention – 2 minsprevention – 2 mins http://www.youtube.com/watch?http://www.youtube.com/watch?

v=TlGe80Mi85Uv=TlGe80Mi85U

ScreeningScreening

What is screening?What is screening? Looking for health problems, (in the right Looking for health problems, (in the right

way)way)A.A. Screening may identify persons Screening may identify persons

needing diagnostic services, but screening is needing diagnostic services, but screening is different from diagnosis.different from diagnosis.

B.B. A process of identifying those at risk A process of identifying those at risk to some health status threat. Diagnosis to to some health status threat. Diagnosis to establish the existence of disease or establish the existence of disease or precursor to a disease should follow.precursor to a disease should follow.

C.C. Screening identifies early disease, Screening identifies early disease, but also must identify individuals at risk so but also must identify individuals at risk so that preventative action can take place that preventative action can take place

D.D. IIndividual benefit, but also to identify ndividual benefit, but also to identify carriers for control of infectious disease. carriers for control of infectious disease. Screening is often based on whether it will Screening is often based on whether it will improve the health of the population.improve the health of the population.

Definition:Definition: ‘‘The presumptive identification of The presumptive identification of

unrecognised disease or defect by unrecognised disease or defect by the application of tests, the application of tests, examinations or other procedures examinations or other procedures which can be applied rapidly. which can be applied rapidly.

Screening tests sort out the Screening tests sort out the apparently wellapparently well persons who persons who probably have a disease from those probably have a disease from those who probably do not.' (Last 1988, who probably do not.' (Last 1988, p118)p118)

Examples:Examples:

breast cancer screening - to detect disease breast cancer screening - to detect disease at an early stage using radiological at an early stage using radiological examinationexamination

colorectal cancer screening - educating colorectal cancer screening - educating population about early signs and symptoms population about early signs and symptoms

cervical cancer screening - detecting cervical cancer screening - detecting abnormalities that could lead to cancer.abnormalities that could lead to cancer.

Post Natal Depression Scale - assists in Post Natal Depression Scale - assists in diagnosis of mothers suffering from diagnosis of mothers suffering from depression.depression.

ScreeningScreening

Colon cancer screeninghttp://www.youtube.com/watch?v=q9M40tN_XBU

STI screening and HIVSTI screening and HIVhttp://www.youtube.com/watch?v=AZg-yeMaVXI

CDC cancer prevention and CDC cancer prevention and detectiondetectionhttp://www.youtube.com/watch?v=t75TFoRiz3s

Why screen for one Why screen for one disease and not disease and not another?another? Is it an important public health problem in Is it an important public health problem in

the society? (SCA screen in China?)the society? (SCA screen in China?) Improve outcomes with earlier diagnosis Improve outcomes with earlier diagnosis

and treatmentand treatment Prevent the onset of a disease altogetherPrevent the onset of a disease altogether

– Need cheap, easy test that can identify sub-Need cheap, easy test that can identify sub-clinical disease (Pap smear)clinical disease (Pap smear)

Effective screening requires Effective screening requires – knowledge of the disease process knowledge of the disease process – information on those at risk information on those at risk – availability of effective treatment.availability of effective treatment.

Schematic representation of the natural Schematic representation of the natural history of diseasehistory of disease

CAB

E

D

OUTCOMES: Death

Chronicity

Residual DisabilityInapparent or

Subclinical

Disease

Clinical Disease

Clinical Horizon

Cure

STAGES OF DISEASE

SUSCEPTIBILITY PATHOGENESISTISSUECHANGES

LEVEL OFPREVENTION

PRIMARYPREVENTION

SECONDARY PREVENTION

TERTIARYPREVENTION

MODES OF Health Promotion Screening Treatment and INTERVENTION Specific Early Detection Limitation of Disability / Rehabilitation

Protection Prompt treatment Chronic Care

Screening criteria - ethical, Screening criteria - ethical, moral, political and economic moral, political and economic issuesissues Identified needIdentified need Prevalence of problem e.g. Sickle cell Prevalence of problem e.g. Sickle cell Possible to identify those at riskPossible to identify those at risk Test acceptable to the population at riskTest acceptable to the population at risk

– E.g. urine test vs. test under general anesthesiaE.g. urine test vs. test under general anesthesia Screening test must be reliable and validScreening test must be reliable and valid Acceptable and effective intervention Acceptable and effective intervention

available - ethicalavailable - ethical Outcome of early intervention superior to Outcome of early intervention superior to

routine diagnosis and treatmentroutine diagnosis and treatment Cost : benefit ratio must be acceptableCost : benefit ratio must be acceptable

Roslin 200 yearsRoslin 200 years