Introduction to Event-Based Surveillance (EBS)

Event-based surveillance (EBS) is the organized and rapid capture of information about events that are a potential risk to public health. This information can be rumours and other ad-hoc reports transmitted through formal channels (i.e. established routine reporting systems) and informal channels (i.e. media, health workers and nongovernmental organizations reports).

They include:

  • Events related to the occurrence of disease in humans, such as clustered cases of a disease or syndromes, unusual disease patterns or unexpected deaths as recognized by health workers and other key informants in the country; and
  • Events related to potential exposure for humans, such as events related to diseases and deaths in animals, contaminated food products or water, and environmental hazards including chemical and radio-nuclear events.

Information received through event-based surveillance should be rapidly assessed for the risk the event poses to public health and responded to appropriately. Unlike classic surveillance, event-based surveillance is not based on the routine collection of data and automated thresholds for action but rather on unstructured descriptions and reports.

Event-based surveillance complements indicator-based surveillance. Both systems should be seen as essential components of a single national surveillance system. When it comes to the timely detection of outbreaks and important public health events, indicator-based surveillance systems often fail. Furthermore, the systems are not suited to the detection of rare but high-impact outbreaks (Severe Acute Respiratory Syndrome, Avian Influenza) or emerging and unknown diseases.

Event-based surveillance systems rely on the immediate reporting of events and are designed to detect:

  • Rare and new events that are not specifically included in indicator-based surveillance.
  • Events that occur in populations which do not access health care through formal channels.


Community health worker assessing a sick child in a community and obtaining vital information.

The sources of reports and rumours for event-based surveillance systems include:

Medical setting: Health care facilities – General practitioners, Health clinics, Hospitals, Pathology services. Allied healthcare professionals and organizations – Community health workers, Midwives/traditional birth attendants, Traditional healers, Laboratories, Ambulance services, Environmental health officers, Health quarantine officers.

Community setting: Community groups – Designated community members, village leaders, village health volunteers, members of the public. Community services – Religious organizations, Nurseries, Schools, Pharmacies, Police, Public utilities (water and sanitation, environmental health) Nongovernmental organizations, Group homes (elderly), Veterinary services. Media and published sources – Media (newspapers, radio, televisions) Academic press, Internet. Others – Military organizations, Embassies, Universities.

In reality, resources are often limited and do not allow surveillance systems to incorporate all of the reporting sources listed above. Therefore, reporting sources for event-based surveillance should be prioritized according to their:

  • Sensitivity: Are they picking up all important events?
  • Sustainability: How easily can they be maintained without undermining other public health programs? 

An event assessment team/unit responsible for assessing each reported event and triggering an immediate response must exist BEFORE event-based surveillance is implemented. At a minimum, the team/unit should exist at the central level. Ideally, the central team should establish strong links with designated local staff who can assist with preliminary event confirmation and, where skills and resources exist, preliminary event assessment.

Rapid response capacity must exist BEFORE event-based surveillance is implemented. National-level response with access to specialist skills (i.e. infection control, laboratory, risk communication). Local response with capacity to conduct a preliminary outbreak investigation.

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