In September 2023, Queensland Health published a Public Health Alert warning commercial food operators to stop using a shredded chicken product after it was identified as the probable source of a Listeria cluster across Queensland (5), New South Wales (3) and Victoria (1). Queensland Health confirmed the strain of Listeria found in the chicken samples was the same as the strain isolated from patients in Queensland hospitals where the product had been used as an ingredient.
What is Listeria?
Listeriosis is usually caused by eating food contaminated by certain types of Listeria bacteria (monocytogenes). While Listeria infection is uncommon and causes few or no symptoms in most of the population, it can be very dangerous for Vulnerable Persons, including pregnant women, adults over 65, and people with weakened immune systems.
The Listeria bacteria is found widely in nature. It may be present in raw foods or may contaminate food after it has been cooked or processed. It can survive and even grow under refrigeration and other food preservation measures, making it challenging to control. Symptoms may include fever, headache, and pains. Less common symptoms are diarrhoea, nausea, and abdominal cramps, and may progress to more serious forms of the illness, such as meningitis and septicaemia. Listeriosis in pregnant women can result in miscarriage, premature birth or, in rare cases, stillbirth. In Australia, it causes approximately 150 hospitalisations and 15 deaths each year.
Due to the public health risk it poses, Listeriosis is classified as a ‘nationally notifiable disease’. Symptoms may appear within 24 hours of eating contaminated food, however, it can take up to two months for them to develop. This can make investigating outbreaks challenging and traceability programs are therefore vital.
What foods are at higher risk of Listeria contamination?
Food Standards Australia New Zealand (FSANZ) identifies the following foods as having a higher risk of Listeria contamination:
- cold meat products, unpackaged ready-to-eat from delicatessen counters, sandwich bars, etc. packaged, sliced ready-to-eat,
- rockmelon (noting the 2018 Australian rockmelon listeriosis outbreak that caused the death of 7 people plus 1 miscarriage)
- cold-cooked ready-to-eat chicken (e.g. as used in sandwiches)
- paté or meat spreads
- pre-prepared fruit and vegetable salads (e.g. packaged salads)
- raw or smoked seafood and chilled seafood (e.g. oysters, sashimi, sushi and prawns)
- soft, semi-soft and surface-ripened cheeses (pre-packaged and delicatessen) e.g. brie, camembert, ricotta, feta and blue
- soft serve ice cream
- unpasteurised dairy products.
The growth and survival of Listeria is influenced by a variety of factors. These include temperature, pH, water activity, salt, and the presence of preservatives. FSANZ has published clear guidance on the ready to eat (RTE) food in which the growth of Listeria monocytogenes will not occur.
Are there processes that can help control Listeria?
Many basic food safety processes can help to control Listeria, including:
- cooking food thoroughly
- reheating food until it is steaming hot
- thoroughly washing fruit and vegetables
- segregation of raw and cooked / ready-to-eat food
- knives and cutting boards used to prepare uncooked foods should not be used to prepare cooked or ready-to-eat food
- eat foods taken out of cold storage within four hours
- maintain good food and personal hygiene practices when handling food
- refrigerating leftovers promptly and using them within 24 hours, or freezing them
- avoiding food that is past its best before or use-by date.
There are multiple guidance documents including ‘Guidance on the application of microbiological criteria for Listeria monocytogenes in RTE food’ and ‘Listeria and Food – Advice for People at Risk’ that can support organisations that cater for the vulnerable. The FSANZ Guide to Food Standards Code 3.3.1 Food Safety Programs for food service to Vulnerable Persons, also provides detailed insight into food safety programs specifically for this group.
However, Listeria remains evasive with regard to its presence in ready-to-eat food. Typical food safety controls are not always effective. Examples of additional measures that may strengthen food safety programs include:
- having a critical focus on menu design, and the potential removal of high-risk foods from the menu
- working closely with suppliers to implement ‘Positive Release’ processes for high-risk products
- ensuring high-risk foods e.g. shredded chicken are only produced in-house using qualified team members
- heightened focus on effective cleaning of equipment used to process RTE foods (e.g. liquidisers and slicers) is also key
- controlled preparation of nutritional supplements, milkshakes, and infant formula.
These additional controls are not mandatory, however, it is easy to understand how they could be of significant support in improving the effectiveness of applicable food safety programs. For those involved in the provision of catering to Vulnerable Persons, regular reviews of the effectiveness of controls, including verification and validation activities, can assist in reducing the risk of Listeria outbreaks. These reviews are particularly impactful following the implementation of changes in the food production environment (e.g. introduction of new kitchen equipment, preparation area modifications, or menu changes).
By applying the recommended controls, guidelines, and processes, and reviewing these regularly, organisations should be better placed to protect themselves and their customers from potentially deadly outbreaks. For a more in-depth look at Food Safety, enrol in our Food Safety Management Systems Lead Auditor course where you’ll get a comprehensive understanding of Food Safety standards including ISO 22000, HACCP, and the National Food Safety Auditor (NFSA) scheme.
