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Evaluation of surveillance systems. Preben Aavitsland. Surveillance. Surveillance is the ongoing systematic collection, collation, analysis and interpretation of data; and the dissemination of information (to those who need to know) in order that action may be taken

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surveillance
Surveillance

Surveillance is the ongoing systematic collection, collation, analysis and interpretation of data; and the dissemination of information (to those who need to know) in order that action may be taken

Information for action!

the surveillance loop
The surveillance loop

Health care system

Surveillance centre

Data

Information

Event

Action

Reporting

Analysis, interpretation

Feedback, recommendations

importance of evaluation
Importance of evaluation
  • Quality
    • Often neglected
    • Basis for improvements
  • Obligation
    • Does the system deliver?
    • Credibility of public health service
  • Learning process
    • EPIET training objective
    • ”Do not create one until you have evaluated one”
general framework
General framework
  • A. Engagement of stakeholders
  • B. Evaluation objective
  • C. System description
  • D. System performance
  • E. Conclusions and recommendations
  • F. Communication
stakeholders
Stakeholders
  • The ”owners” and the ”customers”
  • Users of surveillance system information
    • Public health workers
    • Government
    • Data providers
    • Clinicians
    • etc.
  • Steering group?
  • A condition for change
objective and methods
Objective and methods
  • Specific purpose
  • Scope of evaluation
  • Methods
    • Document studies
    • Interviews
    • Direct observations
    • Special studies
c system description11
C. System description
  • 1 Public health rationale (why?)
  • 2 Objectives (what?)
  • 3 Operations (how?)
  • 4 Resources (how much?)
  • Extreme learning value!!!!
1 rationale for surveillance
The disease

Severity

Frequency

Communicability

International obligations

Costs

Preventability

Society

Public and mass media interest

Will to prevent

Availability of data

1. Rationale for surveillance
2 objectives of system
2. Objectives of system
  • Documented?
    • If not = trouble
  • SMART?
    • Specific
    • Measurable
    • Action oriented[information] in order to [action]
    • Realistic
    • Time frame specified
possible objectives of surveillance
Possible objectives of surveillance
  • Detect outbreaks
  • Monitor trends (by time, place, person)
    • towards a control objective
    • as programme performance
    • as intervention evaluation
  • Estimate future disease impact
  • Collect cases for further studies

….in order to [action]

objectives
Objectives

”To have a continuous overview of the spread of the disease in Norway in order to target preventive measures and plan resource needs.”

3 operations of system
3. Operations of system
  • Health events under surveillance
    • Type of event:exposure -> infection -> disease / outbreaks -> outcome
    • Case definitions
  • Legal framework
  • Organisational framework
  • Components
    • Flow chart
    • Description
the surveillance loop17
The surveillance loop

Health care system

Surveillance centre

Data

Information

Event

Action

Reporting

Analysis, interpretation

Feedback, recommendations

components of system
Components of system
  • Population under surveillance
  • Period of data collection
  • Type of information collected
  • Data source
  • Data transfer
  • Data management and storage
  • Data analysis: how often, by whom, how
  • Dissemination: how often, to whom, how

Confidentiality, security

4 resources for system operation
4. Resources for system operation
  • Funding sources
  • Personell time (= €)
  • Other costs
    • Training
    • Mail
    • Forms
    • Computers
    • ...
system performance
Does it work?

System attributes

Simplicity

Flexibility

Data quality

Acceptability

Sensitivity

Positive predictive value

Representativeness

Timeliness

Stability

Is it useful?

Use of information

Users

Actions taken

Link to objectives

System performance
data quality
Completeness

Proportion ofblank / unknown responses

Simple counting

Validity

True data?

Comparison

Records inspection

Patient interviews

...

Data quality
sensitivity
Sensitivity
  • = reported true cases total true cases
  • = proportion of true cases detected
sensitivity versus specificity
Sensitivity versus specificity

The tiered system: confirmed, probable, possible

measuring sensitivity
Measuring sensitivity
  • Find total true cases from other data sources
    • medical records
    • disease registers
    • special studies
  • Capture-recapture study
slide29

Report

Pos. specimen

Clinical specimen

Seek medical attention

Symptoms

Infected

Exposed

special studies of sensitivity
Special studies of sensitivity
  • 2500 patients with new hepatitis A or B tested (1995-2000)
    • no unreported HIV-cases
  • 70 000 pregnant women tested annually
    • 3-8 undiagnosed HIV-cases (immigrants)
usefulness
Usefulness

Health care system

Surveillance centre

Data

Information

Event

Action

meeting objectives
Meeting objectives?
  • Was information produced?
    • Trends
    • Outbreaks
    • Future impact
    • Cases for further studies
  • Was information used, and by whom?
    • Actions: list
    • Consequences: list
usefulness34
Usefulness
  • Ex 1 (mid 1990s):
    • Information: Aid workers infected in Africa
    • Action: Revision of recruitment policy
  • Ex 2 (1999):
    • Information: Men infected in Thailand
    • Action: Publication --> mass media interest --> = public health warning
conclusions
Conclusions
  • Proper rationale?
  • Attributes
    • Balance of attributes and costs
  • Fulfilling objectives?
  • Recommendations
    • Continue
    • Revise: specify
    • Stop
communicating findings
Communicating findings
  • To stakeholders
  • To data providers
  • To public health community
  • Report
  • Conference presentation
  • Scientific article
scientific publication
Scientific publication
  • Introduction
    • Evaluation objective (B)
  • Material and methods
    • Methods of evaluation (B)
  • Results
    • System description (C)
    • System performance (D)
  • Discussion
    • Sources of error and bias
    • Conclusions and recommendations (E)
  • Acknowledgments
    • Stakeholders (A)
literature
Literature
  • CDC. Updated guidelines for evaluating public health surveillance systems. MMWR 2001; 50 (RR-13): 1-35
  • WHO. Protocol for the evaluation of epidemiological surveillance systems. WHO/EMC/DIS/97.2.
  • Romaguera RA, German RR, Klaucke DN. Evaluating public health surveillance. In: Teutsch SM, Churchill RE, eds. Principles and practice of public health surveillance, 2nd ed. New York: Oxford University Press, 2000.