Listeria in pregnancy- why is it dangerous?
Medically Reviewed by Dr davinder butt
Last updated on 19.06.2023
What is Listeria?
- Listeria (or Listeria monocytogenes to use its full name) is a type of bacteria (germ) found in soil, water, and some animals, such as cattle and poultry.
- Listeria in water and soil can contaminate food crops, and can enter food production facilities or factories in various ways, for example on workers’ shoes, pallets, trolleys and forklifts. It can survive for a long time in cold, moist environments, and can be very hard to get rid of.
- Low levels of Listeria are often present in food and cause no harm, but higher levels can cause serious illness.
- Listeria can cause a severe type of food poisoning in humans, known as Listeriosis.
- There are about 65 reported cases of Listeria each year in Australia, so it is relatively rare. However, because the consequences of Listeria in pregnancy are so severe, it is important for pregnant women to take steps to avoid infection.
What are the symptoms of Listeria?
It depends. There may be no symptoms (silent infection). It can take up to 2 months following exposure for symptoms to appear. Some people get a self-limiting gastro illness with fever, muscles aches, vomiting and diarrhoea. Others may develop a stiff neck, headache, loss of balance, or confusion. If a woman gets Listeria in pregnancy, she may not realise she has it, but it can still cause harm to the developing foetus.
Why is Listeria in pregnancy so serious?
- First of all, pregnant women have a higher risk of getting Listeriosis, as compared to an average healthy adult. A woman’s immune system may be slightly suppressed when she is pregnant, allowing infections to take hold more easily.
- About 1 in 10 cases of Listeria in Australia occur in pregnant women, resulting in death of the developing foetus in about 20% of these women.
- Listeria in pregnancy increases the risk of preterm labour, miscarriage and stillbirth.
- The third trimester seems to be the most risky time.
How does Listeria affect an unborn baby?
If a mum gets Listeria in pregnancy, it can affect the developing foetus in various ways:
- Infection of the lining of the brain (meningitis)
- Infection of the blood (septicaemia)
- Low birth weight
- Learning Disabilities, seizures and other lifelong neurological problems
- Complications involving the brain, kidneys or heart
What to do if you’ve been exposed to Listeria in pregnancy
- If you are pregnant and think you have eaten something contaminated with Listeria (or if you have symptoms of Listeria infection) you should speak to your GP, midwife or obstetrician.
- They may perform some tests and may recommend treatment with antibiotics.
How to avoid Listeria in pregnancy
It’s best to stick to freshly prepared foods, and steer clear of refrigerated, ready-to-eat produce that may have been stored for long periods of time- unlike some other germs, Listeria continues to grow at usual refrigeration temperatures. It is generally possible to eliminate Listeria from food by cooking or pasteurising it. Here is a list of some foods that are best avoided:
- Unpasteurised milk or foods made with unpasteurised milk (such as soft cheese like ricotta, brie and camembert)
- Sliced deli meats (though if carefully reheated to steaming hot just before eating, they can be made safe)
- Cold cooked chicken
- Soft serve ice cream
- Unpasteurised fruit juices
- Hot dogs
- Seed sprouts
- Refrigerated smoked seafood and pre-cooked prawns
- Pâté and meat spreads
- Unwashed raw foods such as fruits, veg & salads
- Pre-cut fruit, veg and salads
- Eggs, meat, poultry or seafood (including sushi) that is raw (or undercooked)
The following foods are generally safe:
- properly cooked meat, chicken, seafood (steaming hot!)
- freshly washed and prepared fruit, veg and salad
- hard cheeses (such as cheddar and parmesan) and pasteurised dairy products
- canned foods
- cooked eggs (so the yolk is no longer runny)
- hard frozen ice cream or gelato
Food safety tips to avoid Listeria in pregnancy
- Hand hygiene- Wash your hands well for at least 20 seconds both before and after handling raw food., and after going to the toilet, changing a nappy or touching an animal.
- Washing produce- wash all raw produce thoroughly under running water before preparing ( though raw meat or poultry should not be rinsed before cooking as droplets can spread bacteria in the kitchen)
- Keep the kitchen clean- wash utensils, work surfaces, and cutting boards with hot soapy water after use. Raw meat, poultry, seafood and eggs should be kept separate from other foods, and should not be prepared on the same surface. Cooked food should not be put on a plate that previously held uncooked food unless it’s been washed beforehand.
- Cooking– cook meat, poultry, seafood, and eggs thoroughly
- Refrigerating- keep your refrigerator below 5 degrees celsius
- If thawing frozen food, do so thoroughly in a refrigerator, microwave, or using cold water. Cook the food straight after thawing
- Don’t leave perishable food at room temperature for more than 1-2 hours (less time if it’s a warm day)
What about eating out during pregnancy?
- avoid the high risk foods listed above
- avoid anything that may have been “pre-made”
- don’t eat anything that is served lukewarm- it’s best to stick with dishes that must be cooked fresh
Further patient resources
Article Resources
Moran LJ, et al (2018). Nutrition and listeriosis during pregnancy: a systematic review
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