Listeria

Listeria is a bacteria that's widely found in dust, soil, water, plants, sewage and animal droppings. It has also been found in a variety of foods, including raw meat, raw vegetables and some processed foods, due to contamination. 

Listeria infection is commonly transmitted to humans by eating contaminated food. The bacteria has been found in a variety of foods at all stages of preparation, from raw to well-cooked leftovers. It's impossible to tell from the appearance, taste or smell whether the food is contaminated with listeria. Listeria is also able to grow on food that's stored in a fridge. 

Less commonly, you can also catch listeria from other people who have the infection, or close contact with farm animals – particularly birthing sheep and cows. 

 People who are at particular risk of serious infection include pregnant women, older people and people with weakened immunity.

• Pregnant women: Pregnant women are 10 to 20 times more likely to get listeria infection than the general population. Even a mild infection in a pregnant woman can cause miscarriage, stillbirth, premature birth or a baby who is very ill when born. Listeria can be passed from mother to baby during pregnancy or birth. Read more about listeria and pregnancy.
• People with weakened immunity: This includes people with cancer, leukaemia, diabetes, AIDS, liver disease and kidney disease. Anyone on medication that lowers their immune system, such as prednisone or cortisone, is also at risk.
  
  

Image credit: Healthify He Puna Waiora

After eating contaminated food, symptoms appear after about 3 weeks on average, but can occur anytime between 3 and 70 days.

Listeria infection can affect people differently. Healthy people usually develop few or no symptoms. However, for some people, the infection can be serious enough to require hospitalisation and may be a threat to life.

Symptoms may include fever, headache, tiredness or aches and pains, which may be accompanied by diarrhoea (runny poo), nausea (feeling sick) and stomach cramps. 

It's not always possible to identify which food caused the illness because it can take so long for symptoms to appear after eating contaminated food. If you're infected, you can excrete the bacteria in your poo for several months. 

Pregnant women

If you're pregnant and get a listeria infection you may not have any any symptoms, or may just experience fever and other flu-like symptoms. Even if you don't feel sick, you can pass the infection to your baby. There is also a risk of stillbirth, miscarriage or premature birth. Read more about listeria and pregnancy.

If you think you've eaten food contaminated with listeria, or if you have any of the symptoms of listeria infection, contact your healthcare provider straight away. Remember that it can take 2 months for symptoms to appear. You may need to take antibiotics to treat the infection and prevent your baby from becoming infected.

Newborn babies

Infected newborn babies may show signs of infection at birth or during the first few days of life. Infection can be very severe for newborn babies and can include pneumonia (lung infection) and meningitis. Infected babies may have severe difficulty with breathing and feeding.

Diagnosis

If you have a fever and other symptoms of possible listeria infection, such as tiredness and muscle aches, within 2 months of eating a possibly contaminated food, you should contact your healthcare provider and tell them you may have eaten contaminated food. They may decide to do further tests.

Treatment

Many healthy adults and children with mild illness only need treatment of the symptoms, such as medicines to treat a high temperature (fever) or increased fluid intake if you have gastroenteritis (infection of your gut). More severe infection may require antibiotics. 

People with severe symptoms will need to be treated in hospital. During pregnancy, prompt antibiotic treatment may help keep the infection from affecting the baby. Read more about listeria and pregnancy.

Safe food handling and safe storage of food is important for everyone.

• Wash your hands before preparing food, and between handling raw food and ready-to-eat foods.
• Keep your kitchen and equipment clean.
• Wash raw fruit and vegetables well before eating.
• Cook all foods of animal origin, including eggs, thoroughly.
• Refrigerate food, including leftovers, as soon as possible after cooking them – ideally within 2 hours once they have reached room temperature. Eat them within 3 to 4 days (or 1 day if you or your whānau are at greater risk of listeria infection).
• May sure your fridge and freezer are cold enough – your fridge should be at 4° C and your freezer at -18° C. Clean your fridge regularly. 
• Follow the storage instructions on packaging and don't eat foods that are past their use-by date.
• Cook leftover foods or ready-to-eat foods, such as hot dogs, until they're steaming hot before eating.
• Keep uncooked meats separate from vegetables, cooked foods and ready-to-eat foods.
• Uncooked meats should also be well wrapped or covered.
• Wash hands, knives and cutting boards thoroughly with hot water and soap after handling uncooked (raw) foods.
• Avoid cross contamination by using separate chopping boards for raw and ready-to-eat foods.
• Take special care when using a microwave to heat food all the way through until it is piping hot.