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2.2.2: Determine the date of detection

The date of detection is the date the public health event was first recorded by any source or in any system. For indicator-based surveillance, the date of detection would be when case or incidence data were recorded (e.g., in a log book, case investigation form, laboratory requisition form). For event-based surveillance (EBS), the date of detection would be when the event information was first recorded (e.g., detected by a media scanning system, recorded by a community health worker, recorded by a hotline operator).

Examples of date of detection, by type surveillance
Detection type Example of date of detection
Indicator-based surveillance (e.g., aggregate data for malaria cases) Malaria outbreaks are declared at the district level in country X. The date of detection of the malaria outbreak in district Y would be the first date on which the district aggregated the data and recorded that the incidence threshold had been exceeded.
Indicator-based surveillance (e.g., case of EVD detected in a health facility) The date of detection would be the date when the health facility recorded a suspected EVD case in any system. Most frequently this is documented by the completion of a case investigation or laboratory requisition form, but may also be indicated on a clinical chart.
Event-based surveillance (e.g., media scanning) A measles outbreak has been occurring in state Z for three weeks, but nobody had aggregated or analyzed the data to record that an outbreak has started. A local newspaper reports on a cluster of deaths among children likely due to measles, which is then picked up by an EBS analyst at the national public health institute. The date of detection of the outbreak would be the date this event was recorded by the EBS analyst.
Event-based surveillance (e.g., community event-based surveillance) A community health worker notices acute flaccid paralysis in a young child on a home visit. The date of detection is the date when the community health worker recorded the suspected polio case (e.g., in a log book, a mobile application, an investigation form).

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