Download - Learning Objectives – Chapter 6 5 Des 2013
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LEARNING OBJECTIVES – CHAPTER 6
1. Relate the different stages of the development of a disease to the phases of prevention.
2. Describe the advantages and disadvantages of population and high-risk prevention strategies.
3. Understand the role and limitations of screening regarding the early detection of disease.
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Overhead 6.1
PRIMORDIAL PREVENTION
Prevention of the emergence of living patterns that contribute to increased risk of disease (e.g., maintenance of low fat diet in Asian
countries).
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Overhead 6.2
PRIMARY PREVENTION
Prevention of disease by controlling risk factors (e.g., non-smoking promotion).
STRATEGIES :PopulationHigh-risk
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Overhead 6.3
PRIMARY PREVENTION :The Population Strategy
Advantages• Radical• Large potential for population• Behaviourally appropriate Disadvantages• Small benefits to individuals• Poor motivation of subject• Poor motivation of physician• Benefit-to-risk ratio may be low
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Overhead 6.4
PRIMARY PREVENTION :The High-risk Strategy
Advantages• Appropriate to individuals• Subject motivation• Physician motivation• Benefit-to-risk ratio is favourableDisadvantages• High screening costs• Temporary effect• Limited effect• Behaviourally inappropriate
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Overhead 6.5
PREVENTION PARADOX
“A preventive measure which brings much benefit to the population often offers little to each participating
individual.”
(Rose, 1985)
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Overhead 6.6
SECONDARY PREVENTION
Reduction in consequences of disease by early diagnosis and treatment (e.g., cervical cancer screening)
TERTIARY PREVENTION
Reduction of complications of disease (e.g., MV crashes and ICU)
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Overhead 6.7
SCREENING
The organized attempt to detect, among apparently health people in the community, disorders or risk factors of which they are
unaware.
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Table 6.1. Levels of prevention
Level of prevention Phase of disease Target
Primordial Underlying conditions leading to causation
Total population and selected groups
Primary Specific causal factors Total population, selected groups and healthy individuals
Secondary Early stage of disease Patients
Tertiary Late stage of disease (treatment, rehabilitation)
Patients
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Table 6.2. Advantages and disadvantages of strategies forprimary prevention
Population strategy High-risk individual strategy
Advantages
• Radical• Large potential for whole population• Behaviourally appropriate
• Appropriate to individuals• Subject motivation• Physician motivation• Favourable benefit-to-risk ratio
Disadvantages
• Small benefit to individuals• Poor motivation of suject• Poor motivation of physician• Benefit-to-risk ratio may be low
• Difficulties identifying high-risk individuals• Temporary effect• Limited effect• Behaviourally inappropriate
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Table 6.3. Criteria for instituting a screening programme
Disease SeriousHigh prevalence of preclinical stageNatural history understoodLong period between first signs and overt disease
Diagnostic test Sensitive and specificSimple and cheapSafe and acceptableReliable
Diagnosis and Facilities are adequate Treatment Effective, acceptable, and safe treatment available
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Table 6.4. Validity of a screening test
Disease statusPresent Absent Total
Positive
NegativeScreening test
a b
c d
a + b
c + d
a + cTotal b + d a + b + c + d
KEY :
a : no. of true positives c : no.of false negatives
b : no. of false positives d : no. of true negatives
Sensitivity = probability of a positive test in people with the disease
= a/(a + c)
Specificity = probability of a negative test in people without the disease
= d/(b + d)
Positive predictive value = probability of the person having the disease when the test is positive= a/(a + b)
Negative predictive value = probability of the person not having the disease when the test is negative= d/(c + d)