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Evaluation of surveillance systems Preben Aavitsland.

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Presentation on theme: "Evaluation of surveillance systems Preben Aavitsland."— Presentation transcript:

1 Evaluation of surveillance systems Preben Aavitsland

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

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 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? °If not = trouble SMART? °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 The surveillance loop Event Action Data Information Health care system Surveillance centre Reporting Feedback, recommendations Analysis, interpretation

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

30 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)

31 Timeliness

32 Usefulness Event Action Data Information Health care system Surveillance centre

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) : °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 °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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