Table 1.

Systematic and grey literature review on event-based surveillance in the field: definitions

EBS	For the purpose of this review, we defined EBS as “the organised collection, monitoring, assessment and interpretation of information of mainly unstructured ad hoc information regarding health events or risks, which may represent an acute risk to human health”2 and require rapid reporting and assessment.2 3 The events can relate to the occurrence of epidemic-prone diseases and other chemical and environmental hazards in humans (eg, cluster of cases of disease, unusual disease patterns, unexplained deaths, chemical spills) or related to potential exposure for humans (eg, mass deaths among animals).2 3 We included EBS systems (as distinct from IBS2) characterised by the following attributes: (1) the source of signal can be a report from the general public, healthcare workers, community-level volunteers and it is not limited to the use of data and other information that arrive via a formal IBS system; (2) notifiable events are not defined by symptoms or syndromes but by (specified or unspecified) events related to health threats; (3) notification from the field to the EBS system is immediate (rather than planned weekly or monthly); (4) every notified signal requires rapid verification; (5) every verified event requires a timely response. EBS as defined by WHO2 can include an epidemic intelligence component that is based on the systematic automated analysis of various media sources (such as Epidemic Intelligence from Open Sources29 and the Global Public Health Intelligence Network30 on global scale). However, given the difference in structure and remit, we restricted our review to field-based EBS sourced from informants in health facilities or in the community.
Signal	A signal is reported data or information which represent a potential acute risk to human health. It is transmitted immediately and has not yet been verified to meet the event definition of the EBS system.2
Event	The IHR define an event as “(…)a manifestation of disease or an occurrence that creates a potential for disease; (…)”.1 In the context of event-based surveillance, an ‘event’ refers to ‘a signal’ that has been verified to meet the event definition of the EBS system.2
Alert	In this document (as in the WHO guidance 20142), “an alert will refer to a public health event that has been (i) verified and (ii) risk assessed and (iii) requires an intervention (an investigation, a response or a communication).”2
Community-based surveillance (CBS)	“CBS is the systematic detection and reporting of events of public health significance within a community by community members”.11 It is a surveillance system (IBS or EBS) that relies on defined individuals from the community (often called community volunteers) who received special training on event definition (for EBS) or case definitions (for IBS) and who notify signals to the surveillance system.
Health facility–based surveillance	A surveillance system (IBS or EBS) that relies on health professionals notifying signals to a next level in the surveillance system.
Open surveillance	We use the term ‘open surveillance’ to describe systems that did not specify who can notify signals but were open to receive signals from anyone (including lay people, media, NGOs, health professionals, teachers etc).
Outbreak setting	Refers to a setting in which EBS was implemented during an outbreak to enhance outbreak-specific surveillance.
Routine setting	Refers to a setting in which the purpose of the EBS system is to contribute to routine surveillance of defined or undefined events to detect outbreaks and other public health emergencies outside outbreaks.

CBS, community-based surveillance; EBS, event-based surveillance; IBS, indicator-based surveillance; IHR, International Health Regulations; NGO, non-government organisation; WHO, World Health Organisation.