PH2610 Applied Epidemiology: Screening for Disease Prevention and Control - PowerPoint PPT Presentation

Loading...

PPT – PH2610 Applied Epidemiology: Screening for Disease Prevention and Control PowerPoint presentation | free to view - id: 4997c-ZDc1Z



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

PH2610 Applied Epidemiology: Screening for Disease Prevention and Control

Description:

Screening for Disease Prevention and Control. Lowell E. Sever, Ph.D. ... Secondary Prevention - Early detection and prompt treatment of disease for cure, ... – PowerPoint PPT presentation

Number of Views:485
Avg rating:3.0/5.0
Slides: 57
Provided by: maryj9
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: PH2610 Applied Epidemiology: Screening for Disease Prevention and Control


1
PH2610 - Applied Epidemiology Screening for
Disease Prevention and Control
  • Lowell E. Sever, Ph.D.
  • September 23, 2002

2
Outline
  • The basic concepts of screening in public health
  • Screening tests Sensitivity, specificity and
    predictive value
  • Selecting cut points for screening tests
  • Screening and the natural history of disease
  • Guidelines for screening programs

3
Outline
  • Genetic screening and public health
  • Why is screening for breast and cervical cancer
    important?
  • Selected issues in cancer screening policy

4
(No Transcript)
5
(No Transcript)
6
Outcomes in the Screening Decision Tree
  • False positive when a screening test indicates
    that the individual has a disease but the person
    in fact does not have the disease.
  • False negative when a screening test indicates
    that the individual does not have a disease but
    the person in fact has the disease.

7
Outcomes in the Screening Decision Tree
  • True positive when the test says the person has
    a disease and the person indeed has the disease.
  • True negative when the test says the person
    does not have the disease and the person in fact
    is disease free.

8
Screening Tests
  • Validity of test is shown by how well the test
    actually measures what it is supposed to measure.
    Validity is determined by the sensitivity and
    specificity of the test.
  • Reliability is based on how well the test does in
    use over time - in its repeatability.

9
Sensitivity and Specificity Tests of Validity
  • Sensitivity is the ability of a screening
    procedure to correctly identify those who have
    the disease--the percentage of those who have the
    disease and are proven to have the disease as
    demonstrated by a diagnostic test.
  • Specificity is the ability of a screening
    procedure to correctly identify the percentage of
    those who do not have the disease--those who do
    not have the disease and are proven to not have
    the disease as demonstrated by a diagnostic test.

10
Screening
  • Diagnosed Disease
  • Status
  • Positive Negative Total
  • Screening test
  • Positive a b a b
  • Negative c d c d
  • Total a c b d

11
Sensitivity and Specificity of Breast Cancer
Screening Examination (HIP Program)
  • Breast Cancer
  • Cancer confirmed Cancer not Total
  • confirmed
  • Screening test
  • Positive 132 983 1155
  • Negative 45 63,650 63,695
  • Total 177 64,633 64,820

12
Screening
  • Predictive Value Positive Probability that a
    person actually has the disease given a positive
    screening test
  • Predictive Value Negative Probability that a
    person is actually disease-free given a negative
    screening test

13
Screening
  • Diagnosed Disease
  • Status
  • Positive Negative Total
  • Screening test
  • Positive a b a b
  • Negative c d c d
  • Total a c b d

14
Predictive Value Positive and Predictive Value
Negative of Breast Cancer Screening Examination
(HIP Program)
  • Breast Cancer
  • Cancer confirmed Cancer not
    confirmed Total
  • Screening test
  • Positive 132 983 1155
  • Negative 45 63,650 63,695
  • Total 177 64,633 64,820

15
Effect of Prevalence on Predictive Value Positive
with Constant Sensitivity and Specificity
  • Prevalence PV () Sensitivity Specifici
    ty
  • () () ()
  • 0.1 1.8 90 95
  • 1.0 15.4 90 95
  • 5.0 48.6 90 95
  • 50.0 94.7 90 95

16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
CONDITIONS FOR WHICH SCREENING IS
RECOMMENDED (U.S. PREVENTIVE SERVICES TASK FORCE
1996)
22
Levels of Prevention (Mausner and Kramer 1985)
  • Primary Prevention - Prevention of the occurrence
    of disease (reduce incidence of disease)
  • Secondary Prevention - Early detection and prompt
    treatment of disease for cure, to slow
    progression, to prevent complications, or to
    limit disability (reduce prevalence of disease)
  • Tertiary Prevention - Limitation of disability
    and rehabilitation where disease has already
    occurred and left residual damage

23
Levels of Prevention
  • Primary Prevention
  • Prevention of the occurrence of disease through
  • General health promotion
  • Specific preventive measures
  • (Mausner and Bahn)

24
Levels of Prevention
  • Secondary Prevention Involves
  • Curing disease at the earliest stage possible
  • Slowing disease progression
  • Preventing complication
  • Limiting disability
  • (Mausner and Bahn)

25
Levels of Prevention
  • Tertiary Prevention
  • Consists of limitation of disability and
    rehabilitation where disease has already occurred
    and left residual damage
  • (Mausner and Bahn)

26
(No Transcript)
27
(No Transcript)
28
Potential Types of Bias in Screening Programs
  • Lead time bias the perception that the cases
    detected through screening have longer survival
    rates simply because the disease was identified
    earlier in its natural history.

29
Potential Types of Bias in Screening Programs
  • Length bias tumors detected by screening tend
    to be slower growing and hence have an inherently
    better prognosis than more rapidly growing tumors
    detected as a result of clinical manifestations.
  • Selection bias individuals motivated to get
    screened may be different than those who are not.

30
(No Transcript)
31
Screening Program Considerations (Guidelines)
  • The disease or condition being screened for
    should be major medical problem.
  • The natural history of the disease or condition
    should be adequately understood, including the
    regular phases and course of the disease, with an
    early period identifiable through screening.

32
Screening Program Considerations (Guidelines)
  • A suitable and effective screening test or
    examination for the disease(s) should be
    available.
  • The screening process should be acceptable to the
    general population.
  • The process should be simple enough to encourage
    large groups of persons to participate.

33
Screening Program Considerations (Guidelines)
  • Policies, procedures, and levels on screening
    tests should be determined in order to establish
    who should be referred for further testing,
    diagnosis, and possible treatment.
  • Access to health care facilities and services for
    follow-up diagnosis and treatment should be
    available for potential cases and for diagnosed
    cases.

34
Screening Program Considerations (Guidelines)
  • Acceptable treatment should be available for
    individuals with diseases identified through the
    screening process.
  • Screening should not be an occasional activity,
    but should be done on a regular and ongoing
    process.

35
Conditions to be Considered in Establishing a
Screening Program
  • The Disease
  • causes significant morbidity and mortality
  • can be identified at a pre-symptomatic stage
    before the individual would ordinarily seek
    medical care
  • responds to acceptable, available and effective
    intervention and treatment
  • is prevalent in the population undergoing
    screening

36
Conditions to be Considered in Establishing a
Screening Program
  • The Test
  • is acceptable to those at risk for disease
  • has adequate sensitivity, specificity and
    predictive value in the target population
  • is available at a reasonable cost
  • is sufficiently standardized to be performed with
    consistency, accuracy and reproducibility

37
Genetic Screening and Public Health
  • Some kinds of genetic screening programs raise
    concerns about the use of genetic screening to
    improve the gene pool - leading to concerns
    about eugenics and programs of racial
    purification.
  • Many of these concerns have been exacerbated in
    recent years with the growth of the Human Genome
    Project.

38
Genetic Screening and Public Health
  • From a public health perspective, genetic
    screening should enable people to make informed
    decisions about their health and that of their
    children in a non-coercive atmosphere.

39
Genetic Screening and Public Health
  • Types of genetic screening that potentially have
    important public health applications and
    implications
  • Heterozygote screening for carriers of recessive
    genetic diseases
  • Prenatal screening to determine if a conceptus
    has specific types of genetic disorders
  • Newborn screening to identify babies with genetic
    abnormalities that are amenable to treatment,
    thus preventing genetic disease by modifying
    the environment

40
Genetic Screening and Public Health
  • Types of genetic screening that potentially have
    important public health applications and
    implications
  • Screening individuals to identify specific genes
    that lead to major diseases before they are
    manifested clinically (presymptomatic testing)

41
Genetic Screening and Public Health
  • Types of genetic screening that potentially have
    important public health applications and
    implications
  • Screening individuals for genes that increase
    their risk for specific diseases
  • Screening individuals for genes that increase
    their risk for developing particular diseases,
    given a specific exposure, that is genetic
    hypersusceptibility

42
(No Transcript)
43
(No Transcript)
44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
47
(No Transcript)
48
(No Transcript)
49
(No Transcript)
50
NIH CONSENSUS STATEMENT Breast Cancer Screening
for Women Ages 40-49
  • Is there a reduction in mortality from breast
    cancer due to screening women ages 40-49 with
    mammography, with or without physical
    examination?
  • How large is the benefit?
  • How does this change with age?

51
NIH CONSENSUS STATEMENT Breast Cancer Screening
for Women Ages 40-49
  • What are the risks associated with screening
    women ages 40-49 with mammography, and with
    physical examination?
  • How large are the risks?
  • How do they change with age?

52
Cervical Cancer Screening Policy/ Guideline
Issues Under Discussion By CDC
  • Screening intervals for Pap testing
  • Upper and lower age limits for Pap testing
  • New Pap testing technologies
  • Recommendations on utilization of Human
    Papillomavirus (HPV) testing

53
Cervical Cancer Screening Interval and Age Limits
  • How often should women be screened?
  • At which age should screening begin?
  • At which age, if any, should screening end?
  • Should the screening interval depend on previous
    screening history?
  • What are other considerations (e.g., risk-based
    screening, practitioners concerns, etc.)?

54
National Breast and Cervical Early Detection
Program (NBCCEDP)
  • Policy Issue I Screening Intervals
  • Reasons why some providers are hesitant to
    discontinue annual screenings
  • The idea that women believe it is important to
    have an annual Pap test
  • The idea that women may receive other preventive
    interventions while visiting the clinician for a
    Pap test

55
National Breast and Cervical Early Detection
Program (NBCCEDP)
  • Reasons why some providers are hesitant to
    discontinue annual screenings (cont)
  • Questionable data indicating that annual Pap
    tests are unnecessary after 3 normal tests
  • Concern that an interval longer than 1 year will
    allow aggressive cancers to escape early
    detection
  • Concern that women will obtain Pap tests at a
    lower frequency than recommended

56
Rescreening Women in the NBCCEDP Conclusions
  • Clinically significant cervical cytologic
    abnormalities are uncommon in the three years
    following a recent normal smear, especially in
    women over age 50
  • Screening more often than every three years in
    such women will likely increase morbidity from
    unnecessary diagnostic evaluations without
    decreasing cervical cancer morbidity or
    mortality.
  • (Sawaya and Washington 1999)
About PowerShow.com