Outbreak investigation

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Overview

The first step in a foodborne outbreak investigation is outbreak identification. A variety of sources may be used to identify outbreaks, including laboratory surveillance networks and public health partners at the local/regional, provincial/territorial, federal, and international levels.

Effective communication and coordination between investigative partners is fundamental to any outbreak investigation. Clear lines of communication and coordinated approach are needed due to the urgency of outbreaks,  the number of investigative partners involved, as well as the volume and variety of shared information.

At the outset of any outbreak investigation, case definitions must be developed. Key criteria should be incorporated into the case definitions, such as laboratory findings, clinical symptoms, and specific information related to person, place and time. Case definition are often revised throughout the investigation as new information becomes available. The initial cases that prompt an outbreak investigation often represent a small fraction of the total number of people affected. Case finding is used to identify additional cases and capture the population at risk of illness.

A number of tools can be used to ensure that a coordinated and well organized investigation takes place. Questionnaires are a systematic way of gathering information needed in an outbreak investigation, usually through interviewing cases. Questionnaires play a key role in hypothesis generation, and they can be used to collect data for both descriptive and analytic studies to more better identify the source of the outbreak. Questionnaires should be designed along with a data management plan. Other important tools include line lists and epidemic curves, which can aid in the organization and orientation of outbreak data and are often used to communicate findings to investigative partners, often in the form of an epidemiological summary.

A key step during outbreak investigations is implementing prevention and control measures to prevent further transmission of illness, additional cases and future outbreaks. Prevention and control activities can be directed at either controlling the implicated source (e.g., food) or controlling the transmission of the pathogen (e.g., person-to-person transmission). Control measures should be considered throughout an investigation to prevent any further illnesses from occurring.

If a suspect food item is identified, an “epidemiological assessment” (or epi assessment) may be prepared. The epi assessment, along with the evidence obtained from the microbiological and food safety investigations, are assessed using a “weight of evidence” approach to inform the overall Health Risk Assessment (HRA).  This can ultimately lead to a recall of the implicated food when appropriate to control the outbreak.

At the conclusion of an investigation, post-outbreak activities such as declaring the outbreak over, OICC deactivation, and creating a final epidemiological summary are often undertaken. Outbreak debriefs help ensure that effective practices are acknowledged and maintained, while areas for improvement are identified to improve practices for future investigations. Finally, knowledge translation and exchange activities help ensure that knowledge is shared and moved into action. 

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Tools

WHO Foodborne disease outbreaks: Guidelines for investigation and control

  • This WHO document provides guidance for anyone who may be involved in the investigation and control of foodborne disease outbreaks.

ECDC Toolkit for investigation and response to Food and Waterborne Disease Outbreaks with an EU dimension

  • This Toolkit provides investigators with a series of tools that can be useful during investigations of food and waterborne disease outbreaks.

PHAC Food Safety Videos

  • This series of four videos provides an overview of how PHAC responds to large outbreaks of foodborne illness. The first video provides an overview, the second and third explain how investigation into the source of the illnesses unfolds, and the fourth provides advice on how to reduce the risk of foodborne illness.

CIFOR Guidelines for Foodborne Disease Outbreak Response (Second Edition)

  • The CIFOR Guidelines for Foodborne Disease Outbreak Response describe the overall approach to foodborne disease outbreaks, including preparation, detection, investigation, control, and follow-up.

Oregon Health Authority Outbreak Investigation Tools

  • This webpage provides a series of templates and tools for use in acute gastroenteritis outbreaks. Most of the templates can be modified by users in order to meet the needs of specific outbreaks.

ECDC Field Epidemiology Manual (FEM Wiki)

  • FEM Wiki is an open information sharing platform for public health experts, hosted and funded by ECDC. FEM Wiki works by sharing knowledge and experience in field epidemiology. If you work in public health and have experience in field epidemiology, then you can make relevant contributions to the texts and discussions.

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