Event-based Surveillance

The Global Disease Detection (GDD) Operations Center serves as CDC’s program dedicated to detecting and monitoring global public health events of international importance using event-based surveillance (EBS). EBS is one of two main types of surveillance used to identify and track infectious diseases and other public health events.

These two types of public health surveillance – event-based surveillance and indicator-based surveillance – complement one another. Both types of surveillance include collecting, monitoring, assessing, and interpreting data. However, the types of data used and the situations in which we use them can be different.

What is event-based surveillance?

Event-based public health surveillance looks at reports, stories, rumors, and other information about health events that could be a serious risk to public health (1). Such information may be described as unstructured information because the information obtained is non-standardized or subjective.

The goal of EBS is to detect unusual events that might signal an outbreak. Information obtained through EBS can come from sources like reports in the media or rumors on an internet blog. EBS can also be community-based, meaning that information about a possible public health event is reported by people in the community through a hotline or other messaging system. For example, if a teacher notices an unusually high number of children absent from school with similar symptoms and reports it to a local health official, the teacher can be considered a participant in community EBS.

What is indicator-based surveillance?

Indicator-based public health surveillance is a more traditional way of reporting diseases to public health officials. Indicator-based surveillance involves reports of specific diseases from health care providers to public health officials. Such information may be described as structured information because the information obtained is standardized.

An example of information obtained through indicator-based surveillance might be reports received on a regular basis and entered routinely into a disease-reporting database on the number of laboratory-confirmed cases of influenza identified at a hospital laboratory (1).

How is event-based surveillance different from indicator-based surveillance?

See the table below for some differences between these two methods:

Comparison of Event-based and Indicator-based Surveillance

Event-based Surveillance

Indicator-based Surveillance

Objectives

Event-based Surveillance: Detect Outbreaks

Indicator-based Surveillance: Detect outbreaks; define disease trends, seasonality, burden, risk factors

Information sources

Event-based Surveillance: Official and unofficial reports of potential disease events from a wide variety of sources including media, rumors, blogs, community members, etc.

Indicator-based Surveillance: Reports of cases of diseases from health care providers, including physicians and hospital laboratories

Information credibility

Event-based Surveillance: Reports need verification to ensure cases meet a specific case definition, and are most credible when supported by laboratory confirmation

Indicator-based Surveillance: Reports are usually credible because health care providers are instructed to only report cases that meet specific case definitions, but the most credible reports involve laboratory-confirmed cases

Timeliness

Event-based Surveillance: May be reported early, even before ill persons have sought medical attention

Indicator-based Surveillance: Reported by health care provider after ill persons have sought medical attention; may sometimes be delayed while awaiting laboratory confirmation or due to reporting requirements.

Where is it used?

Event-based Surveillance: Can be used anywhere

Indicator-based Surveillance: Where health infrastructure exists and health care providers and laboratories are willing to participate in public health surveillance

What diseases is it used for?

Event-based Surveillance: All public health events involving potential disease, including events caused by unknown disease

Indicator-based Surveillance: Usually known diseases

Read About GDD Operations Center for more information on how the GDD Operations Center does event-based surveillance.