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Evaluation of surveillance systems

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Presentation on theme: "Evaluation of surveillance systems"— Presentation transcript:

1 Evaluation of surveillance systems
Preben Aavitsland

2 Information for action!
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!

3 Analysis, interpretation Feedback, recommendations
The surveillance loop Health care system Surveillance centre Event Action Data Information Reporting Analysis, interpretation Feedback, recommendations

4 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”

5 General framework A. Engagement of stakeholders
B. Evaluation objective C. System description D. System performance E. Conclusions and recommendations F. Communication

6 A. Engagement of stakeholders

7 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

8 B. Evaluation objective

9 Objective and methods Specific purpose Scope of evaluation Methods
Document studies Interviews Direct observations Special studies

10 C. System description

11 C. System description 1 Public health rationale (why?)
2 Objectives (what?) 3 Operations (how?) 4 Resources (how much?) Extreme learning value!!!!

12 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

13 2. Objectives of system Documented? SMART? If not = trouble Specific
Measurable Action oriented [information] in order to [action] Realistic Time frame specified

14 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]

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

16 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

17 Analysis, interpretation Feedback, recommendations
The surveillance loop Health care system Surveillance centre Event Action Data Information Reporting Analysis, interpretation Feedback, recommendations

18 Flowchart

19 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

20 4. Resources for system operation
Funding sources Personell time (= €) Other costs Training Mail Forms Computers ...

21 Annual resource needs

22 D. System performance

23 System performance Does it work? System attributes Is it useful?
Simplicity Flexibility Data quality Acceptability Sensitivity Positive predictive value Representativeness Timeliness Stability Is it useful? Use of information Users Actions taken Link to objectives

24 Data quality Completeness Proportion of blank / unknown responses
Simple counting Validity True data? Comparison Records inspection Patient interviews ...

25 Completeness of information

26 Sensitivity = reported true cases total true cases
= proportion of true cases detected

27 Sensitivity versus specificity
The role of lab, cmpylobacteriose i Vest-Agder The tiered system: confirmed, probable, possible

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

29 Seek medical attention
Report Pos. specimen Clinical specimen Seek medical attention Symptoms Infected Exposed

30 Special studies of sensitivity
2500 patients with new hepatitis A or B tested ( ) no unreported HIV-cases pregnant women tested annually 3-8 undiagnosed HIV-cases (immigrants)

31 Timeliness

32 Usefulness Event Action Data Information Health care system
Surveillance centre Event Action Data Information

33 Meeting objectives? Was information produced?
Trends Outbreaks Future impact Cases for further studies Was information used, and by whom? Actions: list Consequences: list

34 Usefulness Ex 1 (mid 1990s): Ex 2 (1999):
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

35 E. Conclusions and recommendations

36 Conclusions Proper rationale? Attributes Fulfilling objectives?
Balance of attributes and costs Fulfilling objectives? Recommendations Continue Revise: specify Stop

37 F. Communication

38 Communicating findings
To stakeholders To data providers To public health community Report Conference presentation Scientific article

39 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)


41 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.

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