Listeria test pregnancy

Listeriosis is usually caught from eating food containing listeria bacteria.

You can get it from lots of types of food, but it's mainly a problem with:

These foods do not always cause listeriosis. If you have eaten them recently, you do not need to do anything unless you get symptoms of the infection.

While the U.S. Centers for Disease Control and Prevention (CDC) have so far announced 55 illnesses and eight deaths linked to the Listeria monocytogenesis outbreak occurring across 14 states, the variable nature of Listeria infections — and foodborne illnesses in general — suggests that many illnesses and some deaths caused by this outbreak may go undiagnosed and unreported.

Among foodborne pathogens, Listeria has a reputation for being particularly deadly. According to CDC estimates, of 1,600 reported Listeria illnesses each year, 260 — 16 percent — result in death.

Almost any severe illness or death attributed to Listeria occurs in people with compromised or weak immune systems, such as developing fetuses, the elderly or otherwise immunocompromised individuals. In healthy adults, the worst cases display flu-like symptoms rarely serious enough to inspire a hospital visit, while many adults consume Listeria without ever feeling the effects.

But because severe Listeria infections share common symptoms with other diseases, and because detecting the bacteria requires a blood test, medical professionals may not properly diagnose listeriosis for each patient hospitalized with the disease.

Compared with other foodborne pathogens, however, the rate of detection for Listeria is actually quite high, according Robert Buchanan, Ph.D., director of the University of Maryland’s Center for Food Safety and Security Systems. He said that estimates suggest Listeria is accurately diagnosed in one of every two medical cases, whereas Salmonella diagnoses are likely closer to one in 30.

“If you get a severe case of listeriosis, it almost always involves hospitalization,” Buchanan said. “Once you’re in there and they start looking around, the probability of them finding it is pretty high.”

Buchanan said that despite the high detection rate, miscarriages likely account for the greatest number of undetected Listeria deaths. Pregnant women infected with Listeria can pass the bacteria onto their developing child without ever realizing they are infected, resulting in miscarriages or stillbirths that might not be accurately attributed to Listeria.

Women should consider testing for Listeria during their second or third trimesters of pregnancy if they have shown any signs of illness similar to listeriosis, particularly if they have eaten high-risk foods such as deli meats or unpasteurized dairy, said Jeff Duchin, M.D., chief of communicable disease control for King County and University of Washington epidemiology professor. If health care providers detect Listeria soon enough, a prompt intravenous treatment of antibiotics can prevent the bacteria from permanently harming the child.

More importantly, Duchin said, pregnant women and other people susceptible to Listeria should consider adjusting their diets.

“In my experience, many people who are at risk of serious Listeria infections need to be more conscious of foods to avoid: Unpasteurized milk and cheese, queso fresco, deli meats, hot dogs, unwashed produce, et cetera,” Duchin said. “Pregnant women and immunocompromised people in general really need to be aware of the risks they’re taking with certain foods and ask whether or not they need to be eating them.”

Among the elderly, some may contract listeriosis during bouts with other medical complications, leading to worsened illnesses without the health care providers realizing they’re infected.

Duchin attributed the relatively high death rate among listeriosis patients to two facts: First, the large majority of people who consume Listeria do not need to seek medical attention, so the statistics do not include them; second, once Listeria invades a certain type of white blood cell known as a macrophage, it appears to be a particularly difficult intruder for weak immune systems to combat.

While Buchanan said that medical professionals in states linked to the Listeria outbreak should be on alert for signs of the bacteria, he and Duchin both said that anyone pregnant or immunocompromised suspecting they could be infected should seek medical attention to get tested.

“If you’ve been exposed to the product in question, you live in the area of the outbreak and you’re experiencing any flu-like symptoms like a fever or joint ache or muscle ache, it’s a very good idea to mention to your healthcare provider that you’re worried about Listeria,” Duchin said.

Buchanan also commented on his surprise that the outbreak has developed in cantaloupe at such a wide scale.

“Usually, you have to have a pretty good slug of Listeria to get infected,” Buchanan said. “So, my question is: How did they get it from this cantaloupe? There’s no question Listeria will grow on cantaloupe, but are cantaloupes getting contaminated by people cutting into the interior without washing them, then leaving them out at room temperature? You need to be sure to wash the surface before you cut it, and then make sure you refrigerate it and eat it within a reasonable time.”

Listeria infection is one of the most serious types of food poisoning. Pregnant women are 10–20 times more likely to get it than the general population. It can cause serious problems for you and your baby. Find out how to avoid it.

1. Listeria infection is caused by eating foods contaminated by Listeria monocytogenes bacteria. Foods most likely to be contaminated include ready-to-eat refrigerated meals and processed foods, eg, cooked and chilled meals, soft cheeses, cold meats, pâtés and smoked fish.
2. Listeria infection can be particularly dangerous for pregnant women. It can cause miscarriage, premature labour or stillbirth, and can also cause infection in your baby.
3. It's impossible to tell from the look, taste or smell whether food is contaminated with listeria. 
4. The best way to avoid listeria infection is to avoid high-risk foods and always follow food safety guidelines.
5. If you think you have eaten food contaminated with listeria or if you have any of the symptoms of listeria infection, contact your doctor or midwife right away. 

Foods to avoid when eating out or buying takeaways, Ministry for Primary Industries brochure, 2020

What is listeria infection?

Listeria infection is caused by eating food contaminated with bacteria called Listeria monocytogenes. It is one of the most serious types of food poisoning.Listeria bacteria are widely found in dust, soil, water, plants, sewage and animal droppings. Due to contamination, they have also been found in a variety of foods, including raw meat, raw vegetables and some processed foods.

Listeria infection is commonly transmitted to humans by eating contaminated food. The bug has been found in a variety of foods at all stages of preparation, from raw to well-cooked leftovers. Listeria can also grow on food stored in a fridge.

What are the symptoms of listeria infection?

The symptoms may be general, such as fever, headache, tiredness, aches and pains, which may be accompanied by runny poos (diarrhoea), feeling sick (nausea) and stomach cramps.

On average, symptoms appear after about 3 weeks but may appear as late as 2 months after you have eaten something with listeria. Many pregnant women do not have any symptoms. Even if you do not feel sick, you can pass the infection to your baby. 

How can listeria infection affect pregnant women?

Pregnant women are 10–20 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. 

How can listeria infection affect my baby?

Listeria can be passed from mother to baby during pregnancy or birth. Newborn babies infected with listeria may show signs of infection at birth or during the first few days of life. 

Infection in newborn babies can be very severe and can include lung infection (pneumonia) and meningitis. Infected babies may have severe difficulty with breathing and feeding.

What should I do if I think I have listeria infection?

If you think you have eaten food contaminated with listeria or if you have any of the symptoms of listeria infection, contact your doctor or midwife right away. Remember that it can take 2 months for symptoms to appear.

How is listeria infection treated?

Your doctor may ask for a blood test to see whether you have listeria infection. You may need to take antibiotics to treat the infection and prevent your baby from becoming infected.

How do I know if my food is contaminated?

Foods that are contaminated with listeria don't look, smell or taste off. Cooking and pasteurisation are the only ways to kill listeria. Listeria will continue to grow in foods in the fridge.

How can I prevent getting listeria infection?

The best way to avoid listeria infection is to avoid high-risk foods and always handle food safely.

High-risk foods that should be avoided

While food safety procedures aim to prevent listeria getting into the foods we eat, there are some foods that are more likely to be contaminated and pregnant women should not eat them.

Avoid all raw and under-cooked seafood, eggs, meat, and poultry while you are pregnant. Do not eat sushi made with raw fish (cooked sushi is safe). Cooking and pasteurisation are the only ways to kill listeria.

Foods that are safe to eat

• Most foods that have been thoroughly cooked (until piping hot) and eaten straight away.
• Vegetables and fruit that have been well washed.
• All tinned foods.
• Breads and cereals (without added mock creams or custards).
• Dried food (fruit, nuts, lentils, beans etc).
• Pasteurised milk and milk products, such as yoghurt, cheese etc.

Safe ways to handle food at home

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.
• Wash raw fruit and vegetables well before eating.
• Cook all foods of animal origin, including eggs, thoroughly.
• Cook leftover foods or ready-to-eat foods, such as hot dogs, until 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 foods.
• Take special care when using a microwave to heat food all the way through until it is piping hot.

Learn more

The NZ Government Ministry of Primary Industries (MPI) in Food Safety (previously called the NZFSA) has a booklet Food safety in pregnancy and other useful resources available to download from the Food safety website

You can also talk to your doctor or midwife and contact the Public Health Unit at your local Community Health Service.

References

Reviewed by

Dr Li-Wern Yim is a travel doctor with a background in general practice. She studied medicine at the University of Otago, and has a postgraduate diploma in travel medicine (Otago). She also studied tropical medicine in Uganda and Tanzania, and holds a diploma from the London School of Hygiene & Tropical Medicine. She currently works in clinical travel medicine in Auckland.