Listeria infection is an illness usually caused by eating food that has been contaminated with the bacteria Listeria monocytogenes. Listeria infection is relatively uncommon; however, the fatality rate can be as high as 30% amongst at-risk people.
Who is at risk of Listeria infection?
Listeria infection can affect people differently. Healthy people may develop few or no symptoms. However, for some people, the infection can be serious enough to require hospitalisation and may even be life-threatening.
People who are at particular risk of serious infection include anyone whose immune system has been weakened, including the following:
- People with cancer including leukaemia
- People with HIV/AIDS
- People suffering from liver or kidney disease
- The elderly
- Pregnant women and their unborn babies
- Anyone on immunosuppressant medications such as prednisone or cortisone.
- Organ transplanted patients
- Newborn babies
Listeria in Pregnancy
During pregnancy, Listeria can manifest as an infection usually leading to a mild illness. A high temperature leading up to or during labour may be the only tell-tale sign. However, even a mild form of the illness can affect the unborn baby and can lead to miscarriage, stillbirth, premature birth or a very ill baby at birth. It is therefore important to minimise exposure to Listeria while you are pregnant.
Healthy people may not show any symptoms. People who fall into any of the at-risk categories above (and in some cases previously healthy people) may show some or all of the following symptoms:
- Aches and pains
- Abdominal cramps
Left untreated, Listeria infection can develop into Meningitis (brain infection) and Septicaemia (blood poisoning).
Symptoms typically appear approximately 3 weeks after exposure to Listeria, but can appear anywhere between 3-70 days after exposure.
Listeria can be effectively treated with antibiotics if detected early.
Where is Listeria found?
Listeria bacteria are most commonly found in soil, silage, sewage, birds and animals. They are also found in some foods including raw meat, raw vegetables and some processed foods.
It is not always possible to identify the source of a person’s Listeria infection because of the time delay between exposure and symptoms appearing.
Outbreaks of Listeria infection due to foods such as soft cheeses, milk, coleslaw, hot dogs and pâté have been reported in Europe, America and Australia.
How can I avoid Listeria infection?
Prevention is better than cure. People at risk from Listeria infection can reduce their risk of infection by:
• Saying no to high risk foods (see below)
• Always handling food safely
• Avoiding contact with any animal afterbirth (their placenta) and with aborted animal foetuses, as Listeria infection has been known to cause illness and abortion in animals.
High risk foods
These foods should be avoided in pregnancy to minimise the chance of Listeria infection:
• Seafood that is ready-to-eat, such as smoked fish or mussels, oysters and raw seafood such as sushi or sashimi
• Coleslaws, fresh fruit salads or any other pre-prepared or stored salads
• Drinks made from fresh vegetables or fruit if the washing procedures are unknown. This does not include canned or pasteurised goods
• Pre-cooked meat products which are eaten without further heating or cooking. Pâté, cured meats (ham, prosciutto and salami), and diced chicken that has previously been cooked (typical in sandwich shops)
• Unpasteurised milk or products made using unpasteurised milk.
• Soft serve ice cream
• Soft cheeses like feta, camembert, ricotta or brie. These are safe if they have been cooked and are eaten hot
• Left over meals and ready-to-eat meals that have been stored in the fridge for more than 1 day
• Dips and salad dressings that have had vegetables previously dipped in them
• Garnishes made from raw vegetables.
- Food that is prepared fresh
- Food cooked fresh to be eaten right away
- Hard cheeses, processed cheese and cheese spreads
- Milk that is UHT and freshly pasteurised
- Pickled or canned food
Safe food handling and storage
Safe food handling and safe storage of food are important for everyone. To those at risk of serious complications of Listeria infection, such practices are especially important. Unlike most other food-contaminating bacteria, Listeria can grow in the refrigerator. However, it is readily killed during cooking. You can reduce the risk of developing Listeria infection and other food-borne illnesses, such as gastroenteritis, by following some basic food hygiene and food storage rules:
- It is best practice to always wash your hands prior to any food preparation and in between handling any raw and ready-to-eat foods.
- Food should be kept covered when in storage.
- Cooked food should be refrigerated within 1 hour of being cooked.
- Raw meat such as poultry and fish should be stored on the lower shelves of the refrigerator to avoid dripping onto other foods.
- Maintain a clean refrigerator that operates below 5 degrees Celsius.
- Observe use-by dates or best-before dates on all refrigerated foods.
- Do not handle cooked and raw foods using the same utensils. These include tongs, knives, and cutting boards. Always ensure such utensils are thoroughly washed after handling raw foods with them.
- Raw fruits, salads and vegetables should be thoroughly washed prior to juicing or consuming. It is recommended to consume them fresh.
- Defrost food using a microwave oven, or by placing it on the lower shelves of your refrigerator.
- Thoroughly cook all food of animal origin. This includes eggs, which should not have runny yolk during pregnancy.
- Ensure all cold foods are kept below 4 degrees Celsius and hot foods above 60 degrees Celsius.
- Reheated food must not be consumed until the internal temperature reaches at least 75 degrees Celsius.
- Read the manufacturer’s instructions carefully when using a microwave oven and always observe the recommended standing times prior to consumption. This is to ensure the food achieves an even temperature before it is eaten.
Any further questions
For further advice, contact your local doctor, specialist, community health centre or maternal and child health nurse.