Listeriosis – advice for people at risk

What is the issue

There are currently a number of multi-state clusters of listeriosis under investigation nationally. Five cases of listeriosis have been reported in Victorian residents this August, the highest monthly total since 2018.

Listeriosis is a relatively rare bacterial infection that may present as a severe, life-threatening, invasive disease in certain high-risk groups.

Who is at risk

People who are at increased risk of listeriosis include:

• Older people (aged over 65 years)
• Pregnant women, and their unborn and newborn babies
• People who have a weakened immune system or are on immune suppressing medication (e.g., corticosteroid medications)
• People with underlying health conditions like cancer, liver or kidney disease, diabetes, cardiac disease and HIV infection.

Symptoms and transmission

Listeriosis is usually caused by eating foods contaminated with the Listeria monocytogenes bacteria, which is widely found in the environment. Listeria can continue to multiply even under refrigeration temperatures and can survive freezing. Thorough cooking of food kills the Listeria bacteria.

The incubation period (period between exposure to infection and developing symptoms) is an average of 3 weeks (but can range from 3 to 70 days).

Common symptoms include fever, intense headache, nausea and vomiting. For people at a higher risk, illness can also present as sepsis, meningitis or meningoencephalitis. Symptoms can worsen very quickly. Listeriosis during pregnancy can lead to miscarriage, stillbirth, premature delivery, or neonatal sepsis.

Healthy adults are generally not affected but may experience mild to moderate flu-like symptoms or gastroenteritis.

Early use of antibiotics can help treat listeriosis, but prevention is best.

Recommendations

For people at increased risk of listeriosis

The best way to prevent listeriosis is to avoid high-risk foods. Listeria cannot be entirely eliminated in these foods, so it is safest not to eat them. Foods commonly associated with Listeria are those with a long shelf-life that are kept refrigerated and have not undergone further cooking. Safer options include foods that are freshly cooked and remain hot.

People at increased risk of listeriosis should not eat:

• Cold meat products eaten without further cooking or heating, as commonly found in delis, sandwich shops or pre-packaged in supermarkets – such as pâté (meat spread), ham, salami, processed/fermented meat products, and cold pre-cooked chicken.
• Unpasteurised milk or foods made from unpasteurised milk.
• Raw fruit, vegetables and herbs that you have not washed yourself, including raw vegetable and herb garnishes.
• Ready-to-eat seafood that will not be further cooked – including smoked seafood (such as fish, mussels, and oysters), raw seafood (such as sashimi, sushi and oysters) and cooked/chilled seafood (such as peeled prawns).
• Pre-prepared, pre-cut, or pre-packaged fruits and vegetables, including those available from greengrocers, supermarkets, buffets, salad bars and sandwich bars.
• Drinks made from fresh or frozen fruit and vegetables where washing procedures are unknown, such as juices and smoothies (excluding pasteurised or canned juices).
• Soft-serve ice-creams.
• Soft cheeses such as brie, camembert, ricotta, blue-vein, and feta.
• Refrigerated ready to eat dips such as hummus, pesto, guacamole and tahini.
• Raw or lightly cooked sprouts including green sprouts like alfalfa and bean sprouts.
• Sandwiches containing any of the high-risk ingredients mentioned above or with a shelf life greater than 2 days.
• Ready-to-eat foods including leftover meats, which have been refrigerated for more than one day and will not be further reheated/cooked.

For health professionals

• Counsel patients at increased risk on the avoidance of high-risk foods.
• Counsel patients at increased risk on the symptoms of listeriosis, so they can seek early medical care if symptoms develop.
• Health services and other settings serving food to patients or clients should not serve high-risk foods to people at increased risk of listeriosis.