Prevention

Question 1

what has improved life expectancy in the last 100 years?

Answer 1

largely better infrastructure and sanitation. improved healthcare has also had a significant impact.

Question 2

what is Geoffrey Rose’s Single Population theory?

Answer 2

a way of looking at interventions and how effective they are based on the impact they have on a population

Question 3

what is a high risk approach to an intervention? example?

Answer 3

identify and treat the “top end” of the population distribution. large individual benefits but small population ones.

case finding/ screening in general practice

Question 4

what is a population approach to an intervention? example?

Answer 4

shift the mean of the entire distribution to the left. large population benefits but small individual ones.

increase exercise; reduce salt in diet; reduce obesity

Question 5

what is primary/secondary/tertiary intervention?

Answer 5

• Primary prevention – preventing onset (behaviour/environment)
• Secondary prevention – catch disease before it is fully fledged (early diagnosis/screening)
• Tertiary prevention – limit disability (rehabilitation)

Question 6

what were the Wanless findings?

Answer 6

• Numerous policy statements and initiatives in the field of public health have not resulted on a rebalancing of policy away from health care (a “national sickness service”) to health (a “national health service”).
• There must be a realignment of incentives in the system to focus on reducing the burden of disease and tackling the key lifestyle and environmental risks.
• Recognising the NHS is only one contributor to delivering the public health agenda ……..

BASICALLY THAT WE SHOULD FOCUS ON PREVENTION MORE INSTEAD OF TREATMENT ALONE.

Question 7

what type of intervention is screening?

Answer 7

secondary

Question 8

what is the definition of screening?

Answer 8

Screening is a public health service in which members of a defined population, who do not necessarily perceive they are at risk of, or are already affected by a disease or its complications, are asked a question or offered a test, to identify those individuals who are more likely to be helped than harmed by further tests or treatment to reduce the risk of a disease or its complications.

Question 9

what is specificity?

Answer 9

• Specificity is the proportion of people without the disease who are correctly re-assured by a negative test result

Question 10

what is sensitivity?

Answer 10

• Sensitivity is the proportion of people with the disease who are identified as having it by a positive test result

Question 11

what is the Positive Predictive Value

Answer 11

• The Positive Predictive Value is the probability that a person with a positive test result actually has the disease

Question 12

what is the Negative Predictive Value

Answer 12

• The Negative Predictive Value is the probability that a person with a negative test result does not actually have the disease.

Question 13

what does a test with high sensitivity provide?

Answer 13

– Maximised identification of diseased people in the screened population
– Relatively few false negatives
– But unnecessary investigations or treatments for others
– Lots of false positives

Question 14

what does a test with high specificity provide?

Answer 14

– detection of only people with the disease
– Relatively few false positives
– But will also miss some people who have or at risk of the disease
– Lots of false negatives

Question 15

when is high sensitivity desirable?

Answer 15

– Adverse consequences of missed diagnosis for the individual e.g. late treatment might be significantly worse than early
– Adverse consequences of missed diagnosis for society e.g. serious communicable disease
– Diagnosis is to be confirmed by other tests so period of anxiety is short, or correct diagnosis is given before treatment is started

Question 16

when is high specificity desirable?

Answer 16

– The diagnosis is associated with anxiety or stigma
– Further investigations are time-consuming, painful or expensive
– Cases are likely to be detected by other means before it is ‘too late’ for effective treatment
– Treatment, especially if painful or expensive, is to be offered without further investigations

Question 17

what is lead time bias?

Answer 17

Early diagnosis falsely appears to prolong survival

(prognosis is the time between diagnosis and death. As those caught by screening are diagnosed earlier, they have a longer prognosis even if they received no beneficial treatment.)

Question 18

what is length time bias?

Answer 18

Screening over-represents less aggressive disease.

(screening is much more likely to catch a less aggressive form of a disease as these less aggressive diseases have longer windows between onset and the time symptoms develop)

Question 19

what is the ethical distinction between screening and normal practice?

Answer 19

Screening has important ethical differences from clinical practice as the health service is targeting apparently healthy people

Question 20

what is an example of a “bad” screening program

Answer 20

Prostate cancer screening/.

Question 21

why is prostate cancer screening limited?

Answer 21

About two thirds of men with an elevated PSA do NOT have prostate cancer detectable at biopsy.

Up to 20% of all men with clinically significant prostate cancer will have a normal PSA

Question 22

what are Wilson and Jungner’s principles and practice of screening for disease

Answer 22

• The condition sought should be an important problem
• There should be an acceptable treatment for patients with recognised disease
• Facilities for diagnosis and treatment should be available
• There should be a recognised latent or early symptomatic stage
• The natural history of the condition, including its development from latent to declared disease, should be adequately understood
• There should be a suitable test or examination
• The test or examination should be acceptable to the population
• There should be agreed policy on whom to treat as patients
• The cost of case-finding (including diagnosis and subsequent treatment of patients) should be economically balanced in relation to the possible expenditure as a whole
• Case finding should be a continuous process and not a ‘once and for all’ project.