Suspected foodborne illness outbreak control guideline

Control Guideline for Public Health Units

Public health priority: High.

PHU response time: Respond on the day of notification. For foodborne illness events thought to be related to a toxin or contamination with a chemical agent, develop a public health investigation plan within 24 hours of notification or immediately if of a serious nature​​​

Case management: Investigate suspected foodborne illness outbreaks to determine if an outbreak has occurred or is occurring and requires investigation and response to control ongoing risk to the public. 

Contact management: Where feasible, advise others at risk about symptoms and preventive actions.

Last updated: 17 February 2026
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NSW guidance

There are no Series of National Guidelines for foodborne illness outbreaks. This document provides NSW guidance on the surveillance and management of suspected foodborne illness outbreaks.

For further detail on operational processes when a foodborne illness outbreak is declared, Public Health Units should refer to the Operational Protocol for the Investigation of Foodborne Illness Outbreaks available on the Infectious Diseases Network SharePoint site. 

​Abbreviations

​HPNSW
Health Protection NSW​
​NCIMS
Notifiable Conditions Information Management System​
​NSWFA
NSW Food Authority​
​OHB
One Health Branch​
PHU​Public health unit​


  1. Reason for surveillance
  2. Case definition
  3. Notification criteria and procedure
  4. The disease
  5. Managing notifications


1. Reason for surveillance

  • To identify if an outbreak is occurring and if so, control the source and prevent further cases
  • To monitor the epidemiology and so inform the development of better prevention strategies.

2. Case definition

Acute onsets of enteric or other symptoms in two or more people from different households where there is a suspected common food or drink source of infection. 

​In rare circumstances, foodborne illness in a single person may require investigation. Examples include:

  • notification of hepatitis A or typhoid in a food handler 
  • locally acquired Salmonella Enteritidis 
  • a disease in a single person that attracts high media interest or has significant social impact (e.g. a death) and is potentially food related
  • food related illness events thought to be related to a toxin or chemical agent (e.g. botulism, histamine and ciguatera poisoning, chemical intoxication from food, sodium nitrite poisoning, illness related to intentional contamination and serious anaphylaxis reactions linked to food). ​​

3. Notification criteria and procedure

​A suspected foodborne outbreak is to be notified to PHUs by telephone within 24 hours of diagnosis by:

  • Hospital CEOs (or delegates)
  • Medical practitioners
Suspected foodborne outbreaks may also be identified through the following:

​1) Complaint (NSWFA, public, medical practitioner, hospital CE)

  • Ill people may make a complaint to the NSWFA (may be directly or via local council) or may send a complaint to their local PHU about a specific venue or event where they suspect they acquired their illness.  
  • If the complaint is made to the NSWFA, they will assess the complaint and send to PHUs via OHB for further investigation if it relates to two or more ill people from different households. 
  • If the PHU identify two or more foodborne illness cases from different households that are suspected to be linked, they will notify OHB, who will advise the NSWFA. 
  • Complaints are assigned to the PHU where the food exposure likely occurred.

2) Routine surveillance

A suspected foodborne illness outbreak may be identified when PHUs and/or OHB undertake routine surveillance. This can only occur if sick people seek medical attention, have a laboratory sample taken, and have a positive result. A possible outbreak may be identified from:
  • PHU routine local surveillance including but not limited to case interviews and disease/serotype/sequencing case count monitoring. 
  • OHB routine surveillance on a state-wide level on disease/serotypes/sequence cluster count analysis.
  • National surveillance: clusters under investigation at a national level will be notified to PHUs from OHB.

3) Suspected toxin or chemical contamination of food

When NSWFA is notified of a food related event that is thought to be related to a toxin or chemical contamination, NSWFA immediately notifies: 

  • OHB (if out of hours, HPNSW out of hours on call number should be used), and/or
  • The NSW Poisons Information Centre. 
OHB will notify other HPNSW teams as relevant (e.g. Environmental Health Branch if the agent is a chemical contaminant) and the relevant PHU.


4. The disease

​ The agent

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.

Mode of transmission

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.

Timeline

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.

Clinical manifestations

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.

Pathogen
 Incubation Period
 Nausea / vomiting
Diarrhoea​
Abdonminal cramps
Fever
Symptom duration
​Staphylococcus aureus
1 - 7 hours
+++​​​
++
+​-​< 2 days​
Bacillus cereus (emetic)

 1 - 6 hours 
 +++
+​
+​
-​< 1 day​
​Bacillus cereus (diarrhoeal syndrome)
8 - 16 hours​-​+++​++​-​< 2 days​
Campylobacter 1 - 10 days +
+++ *​++​++​2 - 10 days​
Clostridium perfringens toxin 6 - 24 hours -
+++​+++​-​< 2 days​
​​Cryptosporidium
​1 - 12 days
​+
+++​+++​-​4 - 21 days​
Listeria monocytogenes # 3 days - 3 months
 -
-​-​++​From days to weeks​
Norovirus 12 - 72 hours
 ++
+++​++​+​1 - 3 days​
Salmonella 8 – 72 hours
+
++​++​++​2 - 7 days​
​Shigella
​12 hours - 6 days
+​+++​++​++​4 - 7 days​
​Shiga toxin-producing Escherichia coli #
​1 - 10 days
-​+++ *​++​-​5 - 10 days​
​Yersinia
1 - 10 days​+​+​+++​+​2 - 3 days​
Vibrio parahaemolyticus 4 – 48 hours​
++
+++​+++​+​1 - 7 days​
Key:  (-)  = usually absent;  (+) = mild;  (++) = moderate;  (+++) = severe;  * = often bloody

# The main manifestations of invasive listeriosis are sepsis and/or central nervous system infection. Neonatal infection typically presents as septicaemia or meningitis. 

Please refer to the Foodborne Pathogen​s Compendium​​​ (found on the Foodborne Illness Outbreak Toolkit SharePoint) for a more comprehensive review of these agents.


5. Managing notifications

Response time

Investigation

On the day the notification of a suspected outbreak is received, begin the follow-up investigation. Within one working day, notify OHB and NSWFA of preliminary findings. When an environmental investigation is required use the Environmental Investigation Request Form.

On notification of a food related event thought to be related to a toxin or chemical contamination, with advice from OHB/ Environmental Health Branch if required, determine the public health response, and inform the NSWFA of the public health investigation plan within 24 hours of notification or immediately if of a serious nature.
​

Data entry

Cases should only be entered into NCIMS if they are diagnosed with a notifiable disease.

Case management

Treatment

Treatment of individual cases is to be managed by their doctor according to diagnosis.

Investigation

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 (e.g., in a high-risk establishment) and further public health risk. 

The purpose of investigation of foodborne illness is to determine if an outbreak is occurring that requires further investigation and public health response. There are two main scenarios to consider: ​

1) Food complaints
The following actions may be taken to investigate a food complaint:

  • Verify the information in the complaint by contacting the complainant. Attempt to obtain the following information if known by the complainant: number of people ill, symptoms, time of symptom onset, duration of symptoms, whether ill people sought health care, specimens collected and results, total number in dining party, foods and drinks consumed by each person in dining party and possible non-food exposures.
  • If the complaint relates to an event, obtain information about where it occurred and who provided the food and drink. 
  • Review medical and laboratory records for complainant and any identified co-diners.
  • If any of the ill people are still sick, ask them to submit a stool specimen for, at minimum, faecal bacterial PCR and MCS, and faecal viral PCR.
  • Contact local health facilities to identify if any other people have presented with similar illnesses around the same time and/or have reported attending the same venue or event.
2) Community clusters
​The following action may be taken to investigate a cluster of cases in the community identified through routine surveillance:

  • Describe the epidemiology of the cases (person, place and time). 
  • Interview cases using the relevant case investigation form.
  • Obtain additional lab testing if not already available (e.g. serotyping, whole genome sequencing).
  • Generate hypotheses about what, if anything, could be a common source for the cases. 
In both scenarios, the PHU should summarise the information gathered and assess if: there is evidence that transmission by food or drink is the likely source, and there could be an ongoing risk of illness to the public. The assessment should be shared with OHB and the NSWFA. If the evidence suggests that a foodborne outbreak could have occurred or be occurring, an outbreak investigation should be initiated. 

PHUs should refer to the Operational Protocol for the Investigation of Foodborne Illness Outbreaks available on the Infectious Diseases Network SharePoint site for detail on operational processes when a foodborne illness outbreak is declared, including identification of lead agency and roles and responsibilities of each stakeholder. Sections 6.1.1 - 6.1.4 of the Protocol also provide further detail on the steps summarised above that can be taken to determine if an outbreak has occurred or is occurring. 

Education

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.

Isolation and restriction

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.

Environmental evaluation

Where a food manufacturer or retailer is a likely source of foodborne illness, contact the NSWFA to:

  • Consider an environmental investigation
  • Advise on control measures
Where contaminated water sources are suspected, PHU environmental health officers will need to investigate and control possible risks, in liaison with the Water Unit, Environmental Health Branch.

Contact management

Identification of contacts

Secondary cases may occur in persons exposed to the faeces or vomitus of cases.

Treatment

No specific treatment is usually recommended to contacts, except for hepatitis A (see Hepatitis A control guideline for public health units).

Education

Provide information to others at risk of illness about the condition, and actions they should take if symptoms develop.

Isolation and restriction

None.
Current as at: Tuesday 17 February 2026
Contact page owner: One Health