Surveillance – an introduction

1. Surveillance – an introduction Preben Aavitsland

2. Surveillance n.Close observation, especially of a suspected spy or criminal ORIGIN C19: 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 • 1839-79 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 • 1880-90s 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. 4th 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; andthe dissemination of information (to those who need to know) in order that action may be taken Information for action!

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

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

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, 1980-1996

18. Ex: To measure the incidence of AIDS to predict future trends and facilitate health service planning Cases of AIDS in a city district, 1990-2004

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 1975-2003

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

21. 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 … Event and population under surveillance

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

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

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 100 000 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 Health care system Surveillance centre Data Information Event Action Reporting Analysis, interpretation Feedback, recommendations

27. Includes (Time, place, person) Clinical features and /or Laboratory results and/or Epidemiological features Should be Clear, simple Field tested Stable and valid Case definition 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. Sensitivity versus specificity Spec Sens

30. 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 Sensitivity and predicitive value

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

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

36. Case definitions and reporting criteria Case definition Measles Confirmednnn nnn nnnn nn Probablenn nnn nnn nnnn Possiblennnnnn nn n nnn Reporting criteria ”Measles” OutputMeasles

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

38. 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 Data sources

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

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 Copy Database Reporting form Interpretation Database

42. Information versus acceptability Accept Info

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

45. 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 Active versus passive surveillance

46. Quality checking • Reporting regularity • Report quality • Follow up procedures

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

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 Health care system Surveillance centre Data Information Event Action Reporting Analysis, interpretation Feedback, recommendations

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