If the outbreak is in an institution, a representative of that institution may also be part of the team. The OMT team leader, who is usually an epidemiologist or public health officer, should clearly define the roles and responsibilities of team members, along with activities required to investigate and contain the outbreak.
Formulate a case definition The case definition may be reviewed and updated during the course of the investigation. A sensitive case definition should be developed initially so it will capture most of the cases, while recognising there will also be some false positives, i. As more information becomes available during the investigation, the case definition can be expanded or refined to ensure that the definition is as specific as needed.
The working case definition should be appropriate and fit the criteria described in Chapter 6. Case finding Appropriate clinical specimens should be collected from cases, including ill staff, in order to confirm a diagnosis and identify the causative agent. Refer to Appendix 3 on specimen collection and notifying the laboratory about the outbreak.
An attempt should be made to identify additional persons who meet the case definition. It may be possible to obtain a guest list or list of attendees from functions, social events or patron booking details if a food premises or restaurant is the place where exposure occurred. Conduct hypothesis generating interviews Public health staff should conduct hypothesis generating interviews of cases to obtain food histories to identify a potential food vehicle or source of infection that may be associated with the illness and can guide further investigation.
Determine source of infection To determine if the outbreak is related to contaminated food at the source or at the point of service by an infected food handler, food handlers should be asked about gastrointestinal illness prior to and during the outbreak.
They should also be asked about their role in food preparation before and during the outbreak, particularly if they were ill at the time.
It may be necessary to collect faecal specimens from food handlers, especially if they are ill with gastrointestinal symptoms at the time of the investigation. Information should also be obtained about people vomiting in the food premises prior to the first onset date of illness in a case. Top of Page Initiate environmental investigation and food sampling It is essential that an EHO inspects catering or food premises if an outbreak of suspected foodborne gastroenteritis has occurred.
Public health agencies may refer to local guidelines and consult with environmental health or local government if a site visit or food testing is to take place. The EHO may assist public health agencies in their investigation by carrying out the following activities at the site visit: sampling of suspect foods and the environment obtaining a copy of the menu or list of foods that were served collecting information on the preparation, storage and distribution of cooked food assessing potential for cross contamination from raw to cooked foods checking for illness among staff and staff absenteeism records interviewing food handlers reviewing and reinforcing general hygiene issues and food control systems implementing control measures where necessary.
In food- or waterborne outbreaks, it is important to collect samples of the suspected vehicle of infection in consultation with environmental health, local government and the public health laboratory.
This is particularly true for norovirus, which is extremely difficult to detect in non-clinical specimens. Carry out trace-back of food products Food production and distribution has become increasingly complex, which requires multiple agencies to collaborate to identify the origins of foods during outbreak investigations [64].
Trace-back is where food safety agencies follow the production and distribution chain of a food to identify where it was grown, processed, packaged, transported and sold at retail. Trace-back of foods is usually only required where foods have become contaminated well before the point of food preparation. For example, Australian and New Zealand outbreaks due to norovirus-contaminated oysters were shown to have originated from Japan and Korea, requiring international trace-back [44, 78].
The main aim of trace back is to determine the source and distribution of the implicated food item and identify potential sites of contamination along the food chain.
External agencies are likely be involved in the trace-back, at local, national and international levels [64]. Analytical study An analytical epidemiological study may be necessary to test a hypothesis or a range of hypotheses. The study uses a comparison group that enables quantitative statistical associations between exposure and illness to be calculated.
Case control and cohort studies are the two most frequently used epidemiological study designs in a foodborne outbreak investigations.
In an institutional outbreak caused by person-to-person transmission, a representative from the institution will update the initial line-list with new information and send it to the PHU. Changes in the outbreak control measures may be indicated from review of these data. If new cases continue to be identified and the nature of the illness changes then a new organism causing infection or a different mode of transmission must be considered. In foodborne investigations, it is critical to continue to monitor for cases to ensure that the contamination has been removed and there is no longer a risk to public health.
The OMT should decide when an outbreak is over. There appears to be no consistency as to when an outbreak of norovirus should be declared over. One recommendation is that outbreaks in residential facilities can be said to be over when seven days have elapsed since resolution of symptoms in the last case. Others have recommended declaring that an outbreak is over when two incubation periods for the organism have passed since the end of symptoms in the last case.
Find information about buying, storing, and serving safe food. Learn more about preventing foodborne illness for those at higher risk including older adults, pregnant women, diabetics, and others.
Consumers who have symptoms of foodborne illness should contact their health care provider to report their symptoms and receive care. To report a complaint or adverse event illness or serious allergic reaction , you have three choices:. Visit www. Follow Us on Twitter. National Case Surveillance. Shereef Elnahal, M. Commissioner P. Box Trenton, NJ Healthy NJ Chronic Disease Prevention Plan New Jersey is home to over 2, licensed hospitals, nursing homes, and medical care facilities.
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