Presentation on theme: "Surveillance – an introduction"— Presentation transcript:
1 Surveillance – an introduction Preben Aavitsland
2 Surveillancen. Close observation, especially of a suspected spy or criminalORIGIN 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 William Farrcollected, analysed, interpreted vital statistics,plotted rise and fall of epidemics of infectious diseasesdisseminated information in weekly, quarterly, and annual reports, medical journals, public presss In Europe and USA doctors must reported communicable diseases1923 Sanepid system started in the Soviet Union1925 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 knowGeneral practice of “epidemiologic intelligence”In 1963
6 In the words of WHO World Health Assembly in 1968: Systematic collection of pertinent dataOrderly consolidation and evaluation of these dataPrompt dissemination of the results to those who need to know"Information for action"
7 SurveillanceSystematic 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 SurveillanceWorld 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 Information for action! SurveillanceSurveillance 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 takenInformation for action!
10 Analysis, interpretation Feedback, recommendations The surveillance loopHealth care systemSurveillance centreEventActionDataInformationReportingAnalysis, interpretationFeedback, recommendations
11 Rationale for surveillance The diseaseSeverityFrequencyCommunicabilityInternational obligationsCostsPreventabilitySocietyPublic and mass media interestWill to preventAvailability of data
12 Priority setting – which diseases? Incidence / prevalenceSeverityEpidemic potentialSocio-economic impactCostPreventabilityPublic concern and news-worthinessFeasibility
13 Possible objectives of surveillance Monitor trends (by time, place, person)towards a control objectiveas programme performanceas intervention evaluationDetect outbreaksEstimate future disease impactCollect cases for further studies….in order to [action]
14 Actions resulting form surveillance …in order to:implement control measures (rapid response)prioritise public health resourcesdesign and plan public health programmesplan and conduct research…
15 SMART objectives Specific Measurable Acceptable and Action-oriented RealisticTime-related
16 Examples Vague... To estimate the frequency of hepatitis C To detect outbreaks of measlesSpecific and action-orientedTo measure the incidence of hepatitis C in France in order to allow planning of specific health care needs for the coming 20 yearsTo 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 yearsCases of poliomyelitis where wild poliovirus was isolatedin 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 therapyIncidence of gonorrhoea and proportion with PPNG in Norway
20 Analysis, interpretation Feedback, recommendations The surveillance loopHealth care systemSurveillance centreEventActionDataInformationReportingAnalysis, interpretationFeedback, recommendations
21 Event and population under surveillance Population and timeEveryone in the country or defined part of the countryPatients in hospitalsEmployees in a factoryAll children in the winter months…EventDiseaseSyndromeAccute flaccid paralysisInfluenza-like illnessDiarrhoeaInfectionPublic health issueAntimicrobial resistanceEnvironmentVector populationWater quality…
22 Seek medical attention DiagnosisPos. specimenClinical specimenSeek medical attentionSymptomsInfectedExposed
23 Seek medical attention DiagnosisLab-confirmed diseasePos. specimenClinical specimenSevere diseaseSeek medical attentionSyndromeMild diseaseSymptomsAsymptomatic infectionInfectedExposed
24 What is better: A system based on clinical cases or a sysem based on laboratory confirmed cases?
25 IndicatorsA calculated measure that indicates the changes you want to monitorDecide one or more indicators that sums up the surveillance resultsFor exampleNumber of casesNumber of cases per population per year (incidence rate)Percentage children under 1 year among meales casesMedian age at first sexual intercoursePercentage unemployed among 50 year olds
26 Analysis, interpretation Feedback, recommendations The surveillance loopHealth care systemSurveillance centreEventActionDataInformationReportingAnalysis, interpretationFeedback, recommendations
27 Case definitionIncludes(Time, place, person)Clinical featuresand /orLaboratory resultsand/orEpidemiological featuresShould beClear, simpleField testedStable and validEx. 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 The role of lab, cmpylobacteriose i Vest-Agder
30 Sensitivity and predicitive value = reported true cases total true cases= proportion of true cases detectedPositive predictive value= reported true cases total reported cases= proportion of reported cases are true cases
31 The tiered case definition ConfirmedThe role of lab, cmpylobacteriose i Vest-AgderProbablePossible
32 Features of different definitions “Confirmed” (specific) case-definitionlow sensitivity - includes few caseshigh specificity - includes mostly true casesfew false positive cases“Possible” (sensitive) case-definitionhigh sensitivity - includes almost all caseslow specificity - includes also many non-casesmany false positive cases
33 Seek medical attention DiagnosisConfirmed casePos. specimenClinical specimenSeek medical attentionProbable caseSymptomsInfectedExposed
43 Aggregation of data Individual data Aggregated data Identified – name, personal id numberNon-identified – but possible to trace backAnonymous – impossible to trace backAggregated dataNumbersTabulated numbers – by sex, age group etc
44 Reporting (data transfer) Data transfer methodPaper by mailTelephoneTelefaxInternetProtected netData transfer frequencyFor every caseDailyWeeklyMonthlyZero reporting
45 Active versus passive surveillance Wait for reporters to reportMay have low sensitivityUsed in most surveillance systemsActiveReach out to potential reporters regularlyMore sensitiveMore resource-demandingUsed for special diseases or periods
46 Quality checking Reporting regularity Report quality Follow up procedures
47 Analysis, interpretation Feedback, recommendations The surveillance loopHealth care systemSurveillance centreEventActionDataInformationReportingAnalysis, interpretationFeedback, recommendations
48 Data analysis and interpretation From data to indicators to interpretationData validation (completeness + validity)Descriptive analysis: time, place, personGenerating and testing hypotheses related to time, place, personAdvanced analysesTime series analysisCluster analysisInterpretationUsing supporting information
49 Analysis, interpretation Feedback, recommendations The surveillance loopHealth care systemSurveillance centreEventActionDataInformationReportingAnalysis, interpretationFeedback, recommendations
50 Information and feedback ContentsSurveillance informationInterpretationsRecommendationsOther informationFormatTextTablesFiguresTarget audiencePublicProfessionalsPolicy makersMediumNewsletterPaperFaxInternetWeb-toolFrequencyImmediatelyDailyWeeklyMonthly
57 Ethical issues: right or wrong Build trust between public health practitioners and the societyIssues:Self-interest or desire to benefit society?Potential benefits and harms. For whom?Maximise benefits. Minimise harmsInvolvement of community representativesRights of peopleConfidentiality – share only with those who have permission from patient or legal right to knowRespect for people
58 Legal issuesSurveillance systems should have a legal foundation that specifiesHow to collect informationHow to use informationNot for other purposesHow to safeguard and store informationHow to allow individuals to see and correct informationMain principlesCollect only what you needChoose the lowest level of identification neededAnalyse and publish rapidly
59 Functions Who does what? Core functions Detection Reporting Investigation & confirmationAnalysis & interpretationAction/responseSupport functionsTrainingSupervisionResourcesStandards/guidelinesWho does what?
60 Resources for system operation Funding sourcesPersonell timeOther costsTrainingMailFormsComputers...
61 Your most important assets A good network of motivated peopleClear case definition and reporting mechanismEfficient communication systemBasic but sound epidemiologyLaboratory supportGood feedback and rapid responseRapid 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 QualityOften neglectedBasis for improvementsObligationDoes the system deliver?Credibility of public health serviceLearning process”Do not create one until you have evaluated one”
65 General framework for evaluation A. Engagement of stakeholdersB. Evaluation objectiveC. System descriptionD. System performanceE. Conclusions and recommendationsF. 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 Is it useful? Use of information Does it work? System attributesSimplicityFlexibilityData qualityAcceptabilitySensitivityPositive predictive valueRepresentativenessTimelinessStabilityIs it useful?Use of informationUsersActions takenLink to objectives