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Epidemiology > Lecture 6 - Disease Prevention I - Screening > Flashcards

Lecture 6 - Disease Prevention I - Screening Flashcards

1
Q

What is the hypothesis about increased likelihood to get HIV?

A

Man is more likely if uncircumcised

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2
Q

Why is circumcision thought to decrease the likelihood of HIV?

A

Foreskin might be an entry point for HIV, so removal might decrease HIV harbouring (grows under the foreskin)

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3
Q

What is the best form of protection against HIV?

A

Condoms - but if minimal condom use (country specific) circumcision seems to be the best idea

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4
Q

When did circumcision appear?

A

During late 19th and early 20th cenury

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5
Q

How many US newborns were circumcised in 1970s?

A

80%

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6
Q

What is screening?

A

Practice of investigating apparently healthy individuals to detect unrecognised disease/its precursors, so measures can be taken to improve prognosis/prevent/delay development of disease

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7
Q

What is the purpose of screening?

A

To detect disease at an early stage (leading to improved prognosis), for risk factors (to ID ppl at increased risk of developing disease, where interventions reduce the risk), to ID ppl with infectious disease (treatment will improve outcome for individual/prevent transmission)

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8
Q

What are the limitations of screening?

A

Can cause false alarms (in healthy ppl) which cause anxiety - e.g. breast cancer (5000 tested) IDs 2820 women with abnormal results which requires further attention, where only 129 have cancer

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9
Q

Give examples of types of screening

A

Screening for high BP/cholesterol and offering lifestyle advice/drug therapy to reduce risk of CVD, chlamydia screening, food handlers for salmonella, health workers for hep B

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10
Q

What is the difference between a screening test and diagnostic test?

A

Screening: should be safe, simple, acceptable, inexpensive, repeatable and valid
Diagnostic are carried out afterwards to confirm diagnosis

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11
Q

What does a screening test aim to do?

A

ID ppl with precursors of condition or at high risk of condition

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12
Q

What is the validity of a test?

A

Ability of test to distinguish between subjects with/without the condition

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13
Q

How do you assess the validity of the screening test?

A

To figure out the true disease status of the individuals using the gold standard

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14
Q

What terms are used to describe validity?

A

Specificity and sensitivity of the test

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15
Q

What is sensitivity of the test (definition)?

A

Ability of test to correctly ID ppl WITH the disease

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16
Q

How do you work out sensitivity?

A

a/(a+c) (Diseased positive/diseased)

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17
Q

What is specificity (definition)?

A

Ability of test to correctly ID ppl WITHOUT the disease

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18
Q

How do you work out specificity?

A

d/(d+b) (Non-diseased negative/non-diseased)

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19
Q

What is the Positive Predictive Value?

A

Likelihood that a patient with a positive result will actually have the disease

20
Q

How do you calculate PPV?

A

a/(a+b) (diseased positive/total positive)

21
Q

What is the Negative Predictive Value?

A

The likelihood that a patient with a negative result will NOT have the dsease

22
Q

How do you calculate NPV?

A

d/(c+d) (non-diseased negative/total negative)

23
Q

What is the predictive value of a test dependent on?

A

Sensitivity/specificity AND the prevalence of the condition in the population

24
Q

What are Receiver Operator Characteristics curves used for?

A

Determine a cut-off value for a diagnostic/screening test

25
Q

How is the cut-off value set for a continuous variable?

A

Proportion of true +ves and false +ves are calculated for possible values - the choice is value which maximises sensitivity and specificity

26
Q

What are the proportions for true and false positives?

A

Sensitivity (diseased +ve/total diseased) and 1-specificity (non-d +ve/total non-diseased)

27
Q

What is the ROC curve?

A

Graphical display of how proportions of true/false positives change for each possible predetermined value

28
Q

What are the limitations in ROC?

A

There is a trade-off between sensitivity and specificity and decision must be based on relative importance

29
Q

What are the different groups that are screened?

A

Whole popn (mass) or specific groups who are thought to have ^ prevalence (targeted)

30
Q

How are people told of the screening programme?

A

Either Systematic (ppl called in for screening) or Opportunistic (ppl presents to dr for other reason and offered a test)

31
Q

Give an example of a systematic test

A

Breast cancer, cervical cancer

32
Q

Give an example of an opportunistic test

A

Chlamydia screening in young ppl, BP screening in old ppl

33
Q

What are the major screening programmes in UK?

A

Antenatal, Neonatal/childhood, Cancers, Infections, CVD

34
Q

What does the antenatal screening test for?

A

Syphilis, HIV, Hep B, rubella, chromosome abnormalities, foetal growth - some offered to all pregnant women, some to those at risk

35
Q

What does the neonatal and childhood screening test for?

A

Newborns: Phenylketonuria, hypothyroidism, Hbopathies, sickle cell
Babies: congenital hip dislocation
Childhood: for hearing and development problems

36
Q

Which cancers are screened for?

A

Breast and cervical in women, Bowel for men and women 60-69

37
Q

Which infections are screened for?

A

Chlamydia in under 25, HIV for those attending sex health clinics, Hep B mandatory for health workers

38
Q

What is screened to prevent CVD?

A

Abdominal aortic aneurysm screening for men (65), diabetic retinopathy screening for diabetics >12YO, targeted/opportunistic screening for BP, high cholesterol, diabetes in 1ry care

39
Q

What are the disease criteria for screening based on WHO?

A

Disease: important health problem, well recognised/detectable pre clinical stage, natural history of disease understood, long period between 1st signs and overt disease

40
Q

What are the 3 main criteria for screening based on WHO?

A

Disease, diagnostic test and diagnosis+treatment

41
Q

What are the diagnostic test criteria for screening based on WHO?

A

Validity, simple/cheap, safe/acceptable, reliable

42
Q

What are the diagnosis/treatment criteria for screening based on WHO?

A

Facilities are adequate, effective/acceptable/safe treatment available, cost effective, sustainable

43
Q

What are the three main issues that should be considered to evaluate a potential screening programme?

A

Feasibility, effectiveness, cost

44
Q

What does feasibility depend on (evaluating screening programme)?

A

Ease to organise the popn to attend screening and whether screening test is acceptable/facilities and resources exist to carry out necessary diagnostic tests after screening

45
Q

How is effectiveness evaluated (screening programme evaluation)?

A

Measuring extent to which screening prog affects subsequent outcomes - difficult to measure due to bias in most studies used: Selection (ppl who participate often differ from those who don’t), Lead time (screening IDs disease that would be ID much later on>so apparent ^survival but due to earlier diagnosis), Length (some conditions slower in development to bad, so more favourable prognosis>conc that screening beneficial in lengthening lives of those found +ve)

46
Q

How does cost affect screening prog evaluation?

A

Resources for healthcare are limited, competing demands for money, cost effectiveness should be considered - costs relate to implementation of screening prog, further diagnostic tests, subsequent cost of treatment BUT w/out screening then costs for treatment with more advanced stage of disease

47
Q

What are the ethical factors that need to be considered when using a screening test (not requested by the patient)?

A

For person, test can do harm as well as benefit; may be risk attached to screening/diagnostic test; false positive results=unnecessary anxiety; unplanned effects of positive test; false negative=false reassurance

Epidemiology (8 decks)

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