Public health priority: High.
PHU response time: Respond to 2 or more probable cases. Respond on the day of notification. Complete summary form within 1 month of completion of the investigation.
Case management: Investigate cause of outbreak, in collaboration with NSW Food Authority (NSW FA). Depending on the likely cause, advise cases who are food handlers or who care for children, the elderly or patients to stay away from such work until at least 48 hours after symptoms cease.
Contact management: Where feasible advise others at risk about symptoms and preventive actions.
Case definitions in an outbreak setting are usually determined by epidemiologists investigating the outbreak.
As a guide, a food-borne disease outbreak may be defined as a situation where 2 or more people who are linked in time or place report acute onset of enteric or other symptoms caused by ingestion of infectious agents or toxins that may have been acquired by consuming contaminated food or drink.
Foodborne illness in two or more related cases is to be notified to PHUs by telephone within 24 hours of diagnosis by:
Many enteric pathogens such as viruses, bacteria and parasites, as well as toxins produced by bacteria (e.g. Staphylococcus aureus), can cause outbreaks of gastroenteritis. Foodborne illness may also be caused by other biological toxins, e.g., mushrooms, or other naturally occurring materials, e.g. cyanide.
Foodborne illness is transmitted by ingestion of contaminated food or drink (by definition). Secondary cases can occur through close contact with infected persons via the faecal oral route.
Many different diseases with different symptoms can result from eating contaminated food or drink. Incubation periods and clinical features of some agents of foodborne illness are presented in the table below.
Depending on the aetiology, symptoms usually last between a few hours and many days, and cases may be infectious while symptoms of diarrhoea or vomiting are present, and for at least 48 hours after symptoms cease.
Symptoms vary depending on the aetiology, and may include nausea, vomiting, diarrhoea, abdominal pain, myalgia, headache, malaise and fever. Some marine toxins produce neurological symptoms.
On the day the notification of an outbreak is received, begin the follow-up investigation. Within one working day, notify the Communicable Diseases Branch (CDB) at email@example.com and the NSW Food Authority Foodborne Outbreak Coordinator of the nature of the outbreak. When an environmental investigation is required use the Environmental Investigation Request Form [PDF].
Cases should not be entered onto NCIMS, except if they are diagnosed with a notifiable disease or if you create an outbreak in NCIMS.
Within one month of completion of the investigation, send the completed OzFoodNet Outbreak Summary Form to the OzFoodNet Epidemiologist, Communicable Diseases Branch.
An outbreak response team should be formed once the existence of an outbreak is verified. The team should meet bt teleconference at least once each working day.
The team members may include the following professionals as required:
The coordinator of the team will usually be the public health unit director (or delegate). When outbreaks cross more than one public health unit, the coordinator should be the public health director (or delegate) in whose jurisdiction the food was prepared or function held. Where interviews are required of cases who live outside the coordinating public health unit's area, the public health unit in which the case resides is responsible for interviewing the case, unless otherwise agreed by the directors of each public health unit. Where a statewide outbreak is identified, the coordinator will be appointed by the Director CDB.
Liaison between NSW Health and the NSW Food Authority during foodborne events is outlined in the Investigation of Foodborne Illness Response Protocol-Operational Procedures Manual.
In investigating a foodborne illness outbreak, close collaboration among investigators is essential.
The responsibility for any epidemiological investigation rests with the Public Health Unit director.
PHUs should not accept specimens of food samples from the public. People bearing samples should be referred directly to the NSW Food Authority.
The responsibility for the environmental food investigation rests with the NSW Food Authority
Public Health and NSW Food Authority staff should conduct at least one onsite assessment together, during the course of the investigation if feasible. The joint on-site assessment should be planned and include a meeting both before and after the assessment to help ensure that all relevant critical inquiry is undertaken and all relevant information and samples are collected. Where a joint on-site assessment is not feasible during the investigation, relevant public heath and NSW Food Authority staff should discuss the joint approach to the investigation to help ensure all relevant critical inquiry is undertaken and all relevant information and samples are collected.
Treatment of individual cases is to be managed by their doctor according to diagnosis.
The response to a notification of a foodborne illness will vary and may be influenced by the number of cases, the aetiology, severity, extent, location (eg., in a high-risk establishment) and further public health risk. Section 6 summarises the steps involved in an outbreak investigation.
There are three main scenarios to consider:
The case or relevant caregiver should be informed about the nature of the infection and the mode of transmission. Emphasise the importance of hand washing, particularly after going to the toilet, changing nappies, before eating and preparing food.
The NSW Food Authority should provide education regarding food safety and hygiene standards in commercial food settings, including institutions.
The PHU should instruct cases who are health care workers, food handlers or who care for children or the elderly not to attend work until at least 48 hours after symptoms cease.
Cases who reside in an institution should be cohorted (separated from non-infected residents) if possible. This should include separate hand washing, toilet and bathroom facilities.
Infants and children attending childcare or school should be excluded from attending for 24 hours after resolution of symptoms.
Where a food manufacturer or retailer is a possible source of foodborne illness, contact the NSW Food Authority Foodborne Outbreak Coordinator to:
Where contaminated water sources are suspected, PHU environmental health officers will need to investigate and control possible risks, in liaison with the Water Unit, NSW Health.
The public health unit and NSW Food Authority staff have joint responsibility for determining whether there is likely to be an ongoing risk to the public from a foodborne illness outbreak stemming from a commercial food premises, and, if so, ensuring that the risk is minimised. The risk may be minimised in a number of ways, depending on the likely cause of the outbreak. These include but are not limited to:
Where an ongoing risk is suspected but the likely vehicle cannot be ascertained following a preliminary epidemiological and environmental investigation, then it may be necessary to suspend the sale of all products that are susceptible to contamination from the likely agent. The NSW Food Authority assesses the evidence in support of a prohibition order under section 60 of the Food Act 2003.
If the Food Authority believes, on reasonable grounds any premises used by a food business in connection with the handling of food intended for sale or any equipment or food transport vehicle is:
The NSW Food Authority is responsible for ensuring a food business' compliance with orders to suspend sale of foods or cease operations. Any enforcement action that the NSW Food Authority considers appropriate will be conducted in accordance with its Compliance and Enforcement Policy. This policy outlines the enforcement tool options that can be utilised by authorised officers.
In the absence of sufficient evidence for an enforcement tool (such as a prohibition order) or where there may be a delay between the date of inspection and issue of a formal Improvement Notice, it may be necessary to provide urgent written direction or advice to a food business to cease production of a food or practice where this is suspected to have contributed to an outbreak. Examples may include advice to cease the use of a raw egg product where microbiological evidence is yet to be determined.
In the absence of the likely vehicle for transmission being identified, factors that should be considered in determining whether or not there is an ongoing risk to the public include:
Where the PHU director considers that there is likely to be an ongoing risk to the public based on the above and supporting epidemiological information, then the PHU director (or delegate) should communicate this to the NSW Food Authority by phone, followed by email or fax. The NSW Food Authority would normally act on the advice of the PHU director, in their lead role, to minimise any ongoing risk to the public, subject to the powers of the NSW Food Act 2003.
Secondary cases may occur in persons exposed to the faeces or vomitus of cases.
No specific treatment is usually recommended to contacts, except for hepatitis A (see protocol).
Provide information to others at risk of illness about the condition, and actions they should take if symptoms develop.
The following are ten steps that provide a systematic approach to investigations. Note that many of these steps will be done concurrently.
Determine whether the number of cases is higher than expected. Information on the background rate of illness in the group can be sought from a range of sources, e.g., surveillance data, hospital records, in patient statistics.
Try to determine likely aetiological agent based on the epidemiological features. Foodborne illness will usually require laboratory investigation to help determine the diagnosis. Alert the laboratory of the outbreak and its suspected aetiology to guide testing procedures. Ask about any specific requirements for the collection of certain specimens and the estimated time frame for results. Stool samples from as many patients as possible should be collected as early as possible after onset of illness.
Each sample should undergo standard bacterial testing and testing for viral pathogens depending on the symptom profile and epidemiology. If needed, further testing (e.g., for toxins) should be determined by the investigation coordinator in consultation with microbiological experts.
A case definition should be developed specifying time, person and place. Cases may be sought from a range of sources, e.g., function organisers, laboratories or hospitals.
Cases (and possibly people who were not ill) will need to be interviewed about risk factors for illness. Development of the questionnaire is often a painstaking process that involves:
Develop a line-listing of cases, including:
Describe the case data in terms of time, place and person:
Identify the group of people who may have been exposed to the aetiological agent.
Consider the source of the illness and the usual mode of transmission based on analysis of the data gathered on the place, time and person characteristics of the cases, and exposure histories.
Perform an analytical study, usually a cohort or a case-control study. In a case-control study, controls must be representative of the population from which the cases arose.
This will include an assessment of the environmental circumstances that could contribute to the outbreak (e.g., food source, storage and handling procedures), further laboratory testing of human, environmental or food isolates, or special epidemiological studies to further determine the risk, e.g., dose response relationships.
This may include recall of product, public warnings, clean up orders, education and training.
Documentation of findings is important to convey science-based recommendations about the immediate control of the outbreak to key personnel, and to provide evidence for policies designed to prevent future outbreaks.