Outbreak Investigation and Response

Outbreak Investigation

• An outbreak is the occurrence of more cases of a disease than expected for a particular place and time.

Identifying Potential Outbreaks

• Review of surveillance data
• Clinician or laboratory reports of unusual diagnoses
• Reports from the public
• Reports from the media

Objectives of a Field Investigation

• Identify the agent, source, and/or mode of transmission
• Characterize the extent of the outbreak (who has been affected, who is at risk)
• Identify exposures or risk factors that increase risk of disease
• Develop and implement control and prevention measures

General Phases of an Outbreak Investigation

Descriptive Phase

• Prepare for fieldwork
• Confirm existence of an outbreak
• Verify the diagnosis
• Construct a case definition
• Find cases systematically and record information
• Perform descriptive epidemiology

Explanatory Phase

• Develop hypotheses
• Evaluate hypotheses epidemiologically
• Reconcile epidemiology with laboratory and environmental findings
• Conduct additional studies as necessary

Response Phase

• Implement and evaluate prevention and control measures
• Initiate or maintain surveillance
• Communicate findings

Components of an Outbreak Field Investigation

• Epidemiology
• Laboratory
• Environmental

Outbreak Case Definitions

• Clinical criteria based on symptoms and signs, laboratory tests
• Epidemiological criteria specifying time, place, person
• Criteria should be objective, simple, accurate, practical, and measurable

Hypothesis Development

• Educated guess about an association between an exposure and outcome, and/or about mode of spread
• Hypothesis should be in a form that allows it to be tested
• Knowledge of the disease, its reservoir, mode of transmission, and other features is probably the most common way of developing hypotheses

Evaluating Hypotheses

• Conduct analytic study
• Comparing hypotheses with collected evidence (laboratory, clinical, environmental, epidemiologic)
• Conduct cohort study or case-control study

Implementing Control Measures

• Prevent further exposure and future outbreaks by eliminating or treating the source
• Initiate as soon as possible

Control Strategies

• Control the reservoir
• Interrupt transmission
• Protect the host

Long-term Response

• Identify why the outbreak occurred
• Determine if conditions still exist that could lead to another outbreak
• Develop strategies to change conditions and reduce the possibility of future outbreaks

Learn about the principles and objectives of outbreak investigation, including identifying potential outbreaks, reviewing surveillance data, and characterizing the extent of the outbreak.