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HSCI 488 EPIDEMIOLOGY > Midterm 2 > Flashcards

Midterm 2 Flashcards

1
Q

What is the ultimate goal in Epidemiology?

A

To control and prevent disease and to improve health.

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2
Q

Why are there no tertiary prevention screening program?

A

Tertiary is to keep the patient comfortable. There is no cure or disease cannot be treated.

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3
Q

What is the purpose of screening?

A

To reverse, halt, or slow down the disease process by detecting it as early as possible in the natural history of that disease.

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4
Q

What is the assumption in screening?

A

Early detection will lead to treatment which will be more effective than later detection.

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5
Q

Give two examples of successful screening programs.

A
  1. Breast cancer.
  2. Prostate cancer.
  3. Cervical cancer.
  4. HIV screening.
  5. Tuberculosis screening.
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6
Q

What is the difference between screening test and diagnostic test?

A

Screening test is used to detect early disease or risk factors for disease in large population. Diagnostic test is to establish the presence or absence of a disease.

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7
Q

What are two measures of Validity?

A

Sensitivity (SE): the ability of a test to correctly identify those with a disease.

Specificity (SP): the ability of a test to correctly identify those do not have a disease. SE and SP are independent of each other.

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8
Q

How do you calculate Sensitivity?

How do you calculate Specificity?

A

DISEASE NO DISEASE

**POSITIVE A B **A + B

**NEGATIVE C D ** C + D

                           A + C               B + D

SENSITIVITY (SE) = A/(A + C)

How good is the test in correctly identifying those with the disease?

SPECIFICITY (SP) = D/(B+D)

How good is the test in correctly identifying those without the disease?

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9
Q

A certain screening test has a sensitivity of 90% and a specificity of 75%. Interpret these values.

A

The test was accurate in identifying 90% of the disease and 75% of the non-disease.

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10
Q

What are true positives and true negatives?

A

True positive: (Box A) sick people correctly identified as sick.

True negative: (Box D) healthy people correctly identified as healthy.

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11
Q

What are false positives and false negatives?

A
  • False positives are healthy people incorrectly identified as sick.
  • False negatives are sick people incorrectly identified as healthy.
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12
Q

What is Overlapping Distributions

A
  • Most screening test do not produce “either or” results
  • There is a set of vallues where persons with and without the disease overlap
  • Point where healthy and sick connect
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13
Q

Cutoff Point

A

Specific value for where a screening test is considered to be positive (and also negative) for disease

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14
Q

How do we determine the best cutoff point to decide positive or negative screening results?

A

By finding the compromise between SE and SP. Choice of cutoff point results in misclassifying some diseased cases as non-diseased and vice versa

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15
Q

Predictive Value Positive

A

Percent of all people who test positive that truly have the disease

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16
Q

Predictive Value Negative

A

Percent of all people who test negative that truly do not have the disease

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17
Q

How do you calculate predictive value positive and predictive value negative?

A

DISEASE NO DISEASE

POSITIVE A B A + B

NEGATIVE C D C + D

Predictive Value Positive (PVP): A/(A+B)

Predicitive Value Negative (PVN): D/(C+D)

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18
Q

How do you interpret predictive value positive and predictie value negative?

A

A patient who tests positive has a (69.6%) probability of having the disease.

A patient who tests negarive has a (98.8%) probability of not having the disease.

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19
Q

How does prevalence affect the predictive values?

A

The predictive values are dependent on prevalence.

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20
Q

What are the criteria for a successful screening program?

A
  • Disease should be an important health problem
  • Accepted treatment for patients with disease
  • Available treatment for diagnosis and treatment
  • Effective intervention
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21
Q

Define Prognosis

A

A prediction of the probable course and outcome of a disease.

The likelihood of recovery from a disease.

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22
Q

When does preclinical phase begin?

A

Biologic onset of disease

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23
Q

What is the middle of the pre-clinical phase?

A

Pathologic evidence of disease

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24
Q

When does the clinical phase begin in the natural history of disease?

A

Signs and symptoms of disease

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25
Q

What is the middle to end of the clinical phase?

A
  1. Medical care sought
  2. Diagnostic
  3. Treatment
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26
Q

Where can we get survival data?

A

CDC, WHO, State and National Public Health Department

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27
Q

What are the 5 ways of expressing prognosis?

A
  • Case-fatality rate
  • Five-year survival rate
  • Observed survival rate
  • Median survival time
  • Relative survival rate
28
Q

Of the 5 methods (expressing prognosis), which method is the most accurate?

A

Relative Survival Rate

29
Q

Which prognosis method can we observe survival using life tables?

A

Observed Survival Rate

30
Q

Which prognosis quantitative expression use for acute diseases and less useful for chronic diseases?

A

Case-fatality rate

31
Q

State the problems for the 5-year survival rate.

A
  1. Difference in screening times
  2. Difference in stage of diseases when screening begins
  3. 5 years is arbitrary
  4. Can be a problem when death occurs less than 5 years
32
Q

Which prognosis method is an age adustment for survival rates?

A

Relative Survival Rate

33
Q

Which prognosis method is a measure of virulence?

A

Case-Fatality Rate

34
Q

Which prognosis method allows for calculation of only half the study population?

A

Medial Survival Rate

35
Q

Give the formula for case-fatality rate.

A

# people who die from disease

people with disease

36
Q

What does a case-fatility rate of 80% mean?

A

Of those who are infected with the disease, 80% will die from the disease.

37
Q

How do you calculate five-year survival?

A

# of people survived the disease after 5 years

The total # of people treated for the disease initially

38
Q

Is it possible to calculate two-year survival?

A

Observed Survival Rate

39
Q

What does a five-year survival rate of 90% mean?

A

After 5 years, 90% of those treated survived.

40
Q

What prognosis method improves upon the limitation of five-year survival?

A

Observed Survival Rate

41
Q

How do we calculate cumulative probabilities?

A

An Outcome

The total # of outcomes

42
Q

What can we construct using cumulative probabilities?

A

Survival Curve

43
Q

Give two reasons why median survival time is preferred over mean survival time?

A
  • Less effected by Outliers
  • Only need to observe half the deaths
44
Q

Define and give the formula for the relative survival rate?

A

Observed survival in diseased Victims

Expected survival if victims had no disease

45
Q

How does it (relative survival rate) improve upon observed survival rates?

A
  • More accurate than observed survival rates
  • Age-adjustment
  • Estimates the chance of surviving the effects of cancer
46
Q

Are survival data usually representative of the general population? Why or why not?

A

Yes because it takes the sample of the general population.

47
Q

Control of Disease

A

Reduction of incidence, prevalence, morbidity and mortality to locally accepted level.

48
Q

Elimination of disease

A

Reduction of disease incidence to zero in a defined geogrphic area.

i.e.: Neonatal Tetamus.

49
Q

Elimination of infection

A

Reduction of infection incidence to zero in a defined geographic area.

i.e.: Measles and poliomyelitis.

50
Q

Eradication

A

Permanent reduction of the worldwide incidence of infection to zero.

51
Q

Extinction

A

The specific infectious agent no longer exists in nature or laboratory.

52
Q

What is the small pox eradication strategy?

A
  • Mass vaccination campaign in each country, using vaccine of ensured potentiacy that would reach 80 >= of population.
  • Development of a system to detect and contain cases and outbreak.
53
Q

How was the small pox symptoms described?

A
  • Severe pain in large and small joints
  • Cough, shaking, listlessness, and langour
  • Postules are red, yellow and white
  • Burning pain
  • Body studded with rice
54
Q

What are the small pox control strategies?

A
  • Small Pox Hospitals (Japan 982 AD)
  • Variolation (10th century AD)
  • Quarantine (1650’s)
  • Home isolation in VA (1667)
  • Jenner vaccination and mass vaccination with Vaccinia
  • Survaillance and containment
55
Q

What are the observation variolation inoculation with small pox pus?

A
  • Pot marked persons are never infected
  • Persons innoculated with small pox pus or dried scabs usually had milder disease
  • Case fatality rate still 2%
  • Can transmit disease to others during illness
56
Q

State the history of small pox vaccination.

A
  • Growth of virus in flank of calf in Italy (1805)
  • Publicity of vaccine production at a medical congress (1864)
  • Most of Europe small pox free (After WWI)
  • Transmission interrupted in Europe and North America (After WWII)
  • Stable freeze-dried vaccine perfected by Collier (1940)
57
Q

State the History of Small pox eradication.

A
  • Pan American Sanitary Organization decides to undertake eredication hemisphere-wide (1950)
  • World Health Assembly adopts goal to eradicate small pox. (1959)
  • World Health Assembly decides to intensifiy eradication and provide more funds (1966)
58
Q

What are the principle indicators of eradicability?

A
  • Humans essential for life cycle
  • Practical diagnostic tools
  • Effective intervention capable of interrupting transmission
59
Q

What are the small pox eredication strategy?

A
  • Mass vaccination for each country, using vaccine of ensured potency that would reach 80 >= of the population
  • Development of a system to detect and contain cases and outbreak
60
Q

What are the assumptions of small pox prior to the eradication programs?

A
  • Highly contagious
  • Vaccine- induced immunity is short lived
  • High vaccination coverage needed to meet herd immunity threashold
61
Q

What was learned about small pox transmission during the eradication program?

A
  • Common transmission: airbone by droplets
    • face to face contact
    • greater transmission by prolonged contact
  • Rare transmission: airbone over long distance
    • more frequently seen in hospitals where coughs were present
    • fomites
  • No carrier state
  • No evidence of transmission by food or water
62
Q

What was learned about small pox during the eradication program?

A
  • Vaccines can provide protection for several years, but full protection decreases over time.
  • Vaccination soon after exposure can provide some degree of protection
  • Transmission does not occur before onset of symptoms
  • Survellience and targed vaccination could significantly decrease transmission during outbreak
63
Q

What are the factors influencing small pox spread?

A
  • Lower temperature/ humidity, higher viability
  • Intensity and duration of contact
  • Length of contagious period
  • Coughing and sneezing
64
Q

What is the most efficient strategy?

A

Surveillience and containment

  • Search for cases
  • Containment of spread by vaccinating primary and their contacts
65
Q

How long is the incubation period?

A

12 days

66
Q

What are the stages of the small pox rash?

A
  1. Macules
  2. Papules
  3. Vesicles
  4. Pustules
  5. Scabs

HSCI 488 EPIDEMIOLOGY (1 decks)

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