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Surveillance – an introduction Preben Aavitsland.

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1 Surveillance – an introduction Preben Aavitsland

2 Surveillance n. Close observation, especially of a suspected spy or criminal ORIGIN C 19: from Fr., from sur- 'over' + veiller 'watch' Source: The Concise Oxford Dictionary. Ed. Pearsall J. Oxford University Press, 2001.

3 Surveillance – original use Close observation of individuals suspected of incubating serious infectious diseases in order to detect initial symptoms of disease in time to institute treatment and isolation. Until 1950s

4 Origins of surveillance William Farr –collected, analysed, interpreted vital statistics, –plotted rise and fall of epidemics of infectious diseases –disseminated information in weekly, quarterly, and annual reports, medical journals, public press s In Europe and USA doctors must reported communicable diseases 1923 Sanepid system started in the Soviet Union 1925 National surveillance system in USA

5 Towards a new concept Alexander Langmuir (1910 – 1993) Continued watchfulness over the distribution and trends of incidence through the systematic collection, consolidation and evaluation of morbidity and mortality reports and other relevant data together with the timely and regular dissemination to those who need to know General practice of epidemiologic intelligence In 1963

6 In the words of WHO World Health Assembly in 1968: Systematic collection of pertinent data Orderly consolidation and evaluation of these data Prompt dissemination of the results to those who need to know " Information for action"

7 Surveillance Systematic ongoing collection, collation and analysis of data and the timely dissemination of information to those who need to know so that action can be taken. Source: A Dictionary of Epidemiology. 4 th edition. Ed. Last J. Oxford University Press, 2001

8 Surveillance World Health Assembly 2005 with the new International Health Regulations The systematic ongoing collection, collation and analysis of data for public health purposes and the timely dissemination of public health information for assessment and public health response as necessary.

9 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!

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

11 Rationale for surveillance The disease Severity Frequency Communicability International obligations Costs Preventability Society Public and mass media interest Will to prevent Availability of data

12 Priority setting – which diseases? Incidence / prevalence Severity Epidemic potential Socio-economic impact Cost Preventability Public concern and news-worthiness Feasibility

13 Possible objectives of surveillance Monitor trends (by time, place, person) –towards a control objective –as programme performance –as intervention evaluation Detect outbreaks Estimate future disease impact Collect cases for further studies ….in order to [action]

14 Actions resulting form surveillance …in order to: implement control measures (rapid response) prioritise public health resources design and plan public health programmes plan and conduct research …

15 SMART objectives Specific Measurable Acceptable and Action-oriented Realistic Time-related

16 Examples Vague... To estimate the frequency of hepatitis C To detect outbreaks of measles Specific and action-oriented To measure the incidence of hepatitis C in France in order to allow planning of specific health care needs for the coming 20 years To detect early time and place clustering of measles cases in order to ensure timely control of outbreaks

17 Ex: To monitor progress towards polio eradication by monitoring the incidence of poliomyelitis where wild poliovirus is isolated in children under 14 years Cases of poliomyelitis where wild poliovirus was isolated in children in a rural district,

18 Ex: To measure the incidence of AIDS to predict future trends and facilitate health service planning Cases of AIDS in a city district,

19 Ex: To monitor trends in the proportion of resistant gonorrhoea in order to guide empiric antibiotic therapy Incidence of gonorrhoea and proportion with PPNG in Norway

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

21 Event and population under surveillance Population and time Everyone in the country or defined part of the country Patients in hospitals Employees in a factory All children in the winter months … Event Disease Syndrome –Accute flaccid paralysis –Influenza-like illness –Diarrhoea Infection Public health issue –Antimicrobial resistance Environment –Vector population –Water quality …

22 Exposed Clinical specimen Symptoms Pos. specimen Infected Seek medical attention Diagnosis

23 Exposed Clinical specimen Symptoms Pos. specimen Infected Seek medical attention Diagnosis Lab-confirmed disease Severe disease Mild disease Asymptomatic infection Syndrome

24 What is better: A system based on clinical cases or a sysem based on laboratory confirmed cases?

25 Indicators A calculated measure that indicates the changes you want to monitor Decide one or more indicators that sums up the surveillance results For example –Number of cases –Number of cases per population per year (incidence rate) –Percentage children under 1 year among meales cases –Median age at first sexual intercourse –Percentage unemployed among 50 year olds

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

27 Case definition Includes (Time, place, person) Clinical features and /or Laboratory results and/or Epidemiological features Should be Clear, simple Field tested Stable and valid Ex. Meningococcal disease is any person with symptoms of meningitis or septicaemia and Neisseria meningitidis detected from blood or cerebrospinal fluid by culture or PCR.

28 Sensitivity versus specificity

29 Sens Spec

30 Sensitivity and predicitive value Sensitivity = reported true cases total true cases = proportion of true cases detected Positive predictive value = reported true cases total reported cases = proportion of reported cases are true cases

31 The tiered case definition Confirmed Probable Possible

32 Features of different definitions Confirmed (specific) case-definition –low sensitivity- includes few cases –high specificity- includes mostly true cases –few false positive cases Possible (sensitive) case-definition –high sensitivity - includes almost all cases –low specificity- includes also many non-cases –many false positive cases

33 Exposed Clinical specimen Symptoms Pos. specimen Infected Seek medical attention Diagnosis Confirmed case Probable case

34

35 Do you want a mainly sensitive or a mainly specific case definition for measles?

36 Case definitions and reporting criteria Case definition Measles Confirmed nnn nnn nnnn nn Probable nn nnn nnn nnnn Possible nnnnnn nn n nnn Reporting criteria Measles Output Measles

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

38 Data sources Hospitals Ambulatory clinics General practitioners Clinics for sexually transmitted diseases Laboratories Selected sites - sentinel surveillance system Schools Work places Existing data collection systems (death certificates, sick leave system etc) Public sector Private sector Non-governmental organisations

39 Exposed Clinical specimen Symptoms Pos. specimen Infected Seek medical attention Diagnosis Laboratories Schools, work places General practitioners Hospitals

40 Issues with differen data sources Cost Representativeness Acceptability Data quality Timeliness Confidentiality

41 Data collection instrument Data form or no specified format? Open or closed questions? Data requirements specified? Reporting form Database Copy Interpretation

42 Information versus acceptability Info Accept

43 Aggregation of data Individual data –Identified – name, personal id number –Non-identified – but possible to trace back –Anonymous – impossible to trace back Aggregated data –Numbers –Tabulated numbers – by sex, age group etc

44 Reporting (data transfer) Data transfer method Paper by mail Telephone Telefax Internet Protected net Data transfer frequency For every case Daily Weekly Monthly Zero reporting

45 Active versus passive surveillance Passive Wait for reporters to report May have low sensitivity Used in most surveillance systems Active Reach out to potential reporters regularly More sensitive More resource- demanding Used for special diseases or periods

46 Quality checking Reporting regularity Report quality Follow up procedures

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

48 Data analysis and interpretation From data to indicators to interpretation Data validation (completeness + validity) Descriptive analysis: time, place, person Generating and testing hypotheses related to time, place, person –Advanced analyses Time series analysis Cluster analysis Interpretation –Using supporting information

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

50 Information and feedback Contents –Surveillance information –Interpretations –Recommendations –Other information Format –Text –Tables –Figures Target audience –Public –Professionals –Policy makers Medium –Newsletter Paper Fax Internet –Web-tool Frequency –Immediately –Daily –Weekly –Monthly

51 Web tool – example from Norway

52 Feedback has its own value Shows respect for those who report Increases adherence to system Forces you to analyse and interpret

53 What is the feedback from the surveillance system in your country?

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

55 Information for action! Surveillance is not for archives! Action –implement control measures rapid response –prioritise public health resources policy change? –design and plan public health programmes

56 If there is no action....it isnt surveillance

57 Ethical issues: right or wrong Build trust between public health practitioners and the society Issues: –Self-interest or desire to benefit society? –Potential benefits and harms. For whom? –Maximise benefits. Minimise harms –Involvement of community representatives –Rights of people Confidentiality – share only with those who have permission from patient or legal right to know –Respect for people

58 Legal issues Surveillance systems should have a legal foundation that specifies –How to collect information –How to use information Not for other purposes –How to safeguard and store information –How to allow individuals to see and correct information Main principles –Collect only what you need –Choose the lowest level of identification needed –Analyse and publish rapidly

59 Functions Core functions Detection Reporting Investigation & confirmation Analysis & interpretation Action/response Support functions Training Supervision Resources Standards/guidelines Who does what?

60 Resources for system operation Funding sources Personell time Other costs –Training –Mail –Forms –Computers –...

61 Your most important assets A good network of motivated people Clear case definition and reporting mechanism Efficient communication system Basic but sound epidemiology Laboratory support Good feedback and rapid response Rapid reporting Analysis Action

62 Identify two major weaknesses in the surveillance system for communicable diseases in your country

63 Evaluation of surveillance systems Systematic investigation of the merit of the surveillance system in order to increase its usefulness and efficiency

64 Importance of evaluating surveillance systems Quality –Often neglected –Basis for improvements Obligation –Does the system deliver? –Credibility of public health service Learning process –Do not create one until you have evaluated one

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

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

67 D. 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

68 Timeliness

69 E. Conclusions and recommendations Proper rationale? Attributes –Balance of attributes and costs Fulfilling objectives? Recommendations –Continue –Revise: specify –Stop

70 Surveillance – a big challenge Crude Inaccurate Incomplete Cumbersome Complex


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