Slide 1
Surveillance turns health reports into a signal for action
Disease surveillance systematically collects and interprets health information. Its purpose is to guide action, not simply accumulate a list of illnesses.
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Information must reach people who can use it. Dissemination is therefore part of surveillance itself: a carefully analyzed pattern has limited practical value if it never informs a response.
Slide 2
A shared case definition makes counts comparable
Surveillance systems specify what counts as a case. Consistent definitions help make reports from different places or periods comparable.
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A surveillance definition serves population monitoring and may differ from a clinician’s assessment of an individual. Counting rules need consistency, while clinical decisions can use a wider and changing body of information.
Slide 3
Different information streams offer different clues
Laboratory reports, clinical diagnoses and symptom patterns can each provide information. Some signals arrive sooner but are less specific.
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Syndromic surveillance follows patterns such as groups of symptoms before a confirmed diagnosis is available. That can provide an early warning while still requiring investigation of what is producing the pattern.
Slide 4
More reports do not always mean more illness
A rise in reports can reflect more illness, better detection or changed reporting. Interpreting a trend requires examining how the data were produced.
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Access to testing and participation by reporting services affect what becomes visible. Stable collection methods improve comparisons, while a change in methods needs to be considered before attributing every increase to transmission.
Slide 5
A useful signal must reach investigation or prevention
Surveillance can prompt investigation, prevention or resource planning. It also needs evaluation to see whether it delivers useful information in time.
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An elaborate system can collect more detail than decision-makers can use. The appropriate balance between speed, completeness and precision depends on the health question and the actions the system is meant to support.