Surveillance – an introduction Preben Aavitsland

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.

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

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

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

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"

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

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.”

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!

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

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

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

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]

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 …

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

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

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

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

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

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

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 …

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

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

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

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

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

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.

Sensitivity versus specificity The role of lab, cmpylobacteriose i Vest-Agder

Sensitivity versus specificity

Sensitivity and predicitive value = 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

The tiered case definition Confirmed The role of lab, cmpylobacteriose i Vest-Agder Probable Possible

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

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

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

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

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

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

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

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

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

Information versus acceptability

Aggregation of data Individual data Aggregated 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

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

Active versus passive surveillance 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

Quality checking Reporting regularity Report quality Follow up procedures

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

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

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

Information and feedback 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

Web tool – example from Norway

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

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

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

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

If there is no action.. ..it isn’t surveillance

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

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

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

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

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

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

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

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”

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

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

D. System performance Is it useful? Use of information 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

Timeliness

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

Surveillance – a big challenge Crude Inaccurate Incomplete Cumbersome Complex