What is listeria?
Listeria infection, also known as listeriosis, is caused by the bacteria Listeria monocytogenes (L. monocytogenes). The Centers for Disease Control and Prevention (CDC) estimates that
These bacteria are most commonly found in foods that include:
- unpasteurized or raw dairy products
- certain deli meats
- raw vegetables
Listeriosis isn’t serious in most healthy people, who may never experience symptoms or complications of the infection. However, for some people, this infection can be severe or life threatening.
Treatment depends on how severe the infection is and your overall health. Proper food safety can help reduce your risk of developing listeriosis.
Other potential symptoms may include:
In this type of listeriosis, symptoms can begin
In some cases, listeriosis can spread outside your intestines. This more advanced infection, known as invasive listeriosis, causes more severe symptoms. These include:
People with invasive listeriosis often do not experience the first symptoms until
Invasive listeriosis is serious and can cause dangerous complications if left untreated.
According to the American College of Obstetricians and Gynecologists, pregnant people are 10 times more likely to get listeriosis than the general population. Currently, scientists are unsure as to why pregnancy increases the risk of getting the infection.
If you’re pregnant, you may not have any symptoms or the symptoms may be so mild that you don’t realize you have listeriosis.
Additionally, as in invasive listeriosis, symptoms can take a while to show up, often between
When present, the typical symptoms of listeriosis in a pregnant person are flu-like, including:
- fever, with or without chills
- body aches
A Listeria infection in a newborn can cause serious, often life threatening illness and complications. Symptoms of listeriosis in a newborn can include:
Listeriosis in newborns is divided into
- Early onset. Early onset listeriosis happens within 6 days of birth. A newborn acquires the infection from their parent’s placenta. Early onset infections typically cause meningitis, septicemia (blood infection), and pneumonia.
- Late onset. Late onset listeriosis happens between 7 to 28 days after birth. Medical professionals believe newborns with this type of listeriosis get the infection during delivery or due to an exposure in the hospital. It tends to cause meningitis and septicemia.
The potential complications of listeriosis include:
- bacterial meningitis, inflammation of the membranes surrounding the brain and spinal cord
- encephalitis, inflammation of the brain
- endocarditis, an infection and inflammation of the inner lining of the heart
- septicemia, an infection of the bloodstream
- pneumonia, an infection of the lungs
- osteomyelitis, an infection of the bone
- septic arthritis, an infection of the joints
- sepsis, a life threatening condition that’s caused by your body’s response to an infection
Listeriosis develops after you come into contact with the bacteria L. monocytogenes. Most commonly, a person gets listeriosis after eating contaminated food. A newborn can also get it from their mother.
Listeria bacteria live in soil, water, and animal feces. They can also live on food, on food production equipment, and in cold food storage. Listeriosis is commonly spread by:
- processed meats, including deli meat, hot dogs, meat spreads, and refrigerated smoked seafood
- unpasteurized dairy products, including soft cheeses and milk
- some processed dairy products, including ice cream
- raw vegetables and fruit
Listeria bacteria can still grow in cold environments, such as refrigerators, although they don’t grow as quickly. They can also survive freezing temperatures, which means that they can be present in frozen foods that have been thawed.
A 2020 study collected samples of frozen fruit and vegetables from retail and catering locations. Researchers were able to detect L. monocytogenes in 10 percent of the frozen vegetables. Some of the bacterial strains matched those that had caused previous infections in people.
These bacteria are more likely to be destroyed by heat. Heating processed foods, like hot dogs, to 165°F (73.8°C) will kill the bacteria.
Healthy people will rarely become ill because of Listeria. If you do, the illness is typically mild and goes away on its own.
Those at an increased risk of serious illness or complications from listeriosis include:
- pregnant people
- individuals over age of 65
- those with a weakened immune system, which can happen due to:
- immunosuppressant medications, such as prednisone or medications prescribed to treat autoimmune diseases like rheumatoid arthritis or lupus
- organ transplants
A variety of foods have been previously linked to Listeria
Soft cheeses are produced from milk that hasn’t been pasteurized. Pasteurization is a process that helps kill potentially harmful microbes in certain types of foods. Some examples of soft cheeses include:
To see if a specific cheese is pasteurized, check the label. It should say something along the lines of “made with pasteurized milk.” If you’re in doubt about whether or not a product is pasteurized, it’s best not to buy it.
Raw milk hasn’t been pasteurized to kill harmful microbes. Keep in mind that raw milk can also be used to make other dairy products like cheese, yogurt, and ice cream.
Similar to soft cheeses, check the product label to see if a product is made with pasteurized milk.
Listeria can potentially be found in several different types of ready-to-eat meat products. These include:
- deli meats
- cold cuts
- hot dogs
- pâté or other meat spreads
- smoked fish
If you’re at risk of serious listeriosis, it’s generally best to avoid these items unless they’ve been cooked to a safe temperature, such as 165°F (73.8°C).
Pâtés, meat spreads, or smoked fish that are shelf-stable are typically safer. Shelf-stable means that an item can be stored at room temperature prior to opening. A good rule of thumb is to avoid selecting items found in the refrigerated section of the store.
Raw fruits and vegetables
Since Listeria can be found on raw fruits and vegetables, be sure to wash or scrub these foods under running water before preparing or eating them.
This is important even if you don’t plan on eating the skin or peel, as bacteria found on the peel can get into the food as you prepare it.
For melons in particular, take steps to consume them safely. Aim to eat cut melon right away. Otherwise, store it safely in a refrigerator. Throw away any remaining cut melon in your refrigerator after a week has passed.
Raw sprouts can harbor Listeria as well as a variety of other bacteria like Escherichia coli (E. coli) and Salmonella. Unlike other types of fresh vegetables, washing raw sprouts isn’t effective at removing bacteria.
If you’re at risk of severe listeriosis, make sure any sprouts are thoroughly cooked before eating them. Avoid consuming sprouts that are raw or even lightly cooked.
Some foods can still become contaminated with Listeria during production, processing, or packaging. Because of this, always adhere to appropriate food safety practices when handling, preparing, and cooking food.
If a specific product is found to be contaminated with Listeria, the company that produces it will issue a recall. Be sure to stay up-to-date on current recalls. If you have a food item affected by a recall, throw it away or return it to the store.
If you’re otherwise healthy and have eaten food that may have been contaminated with Listeria, monitor yourself for symptoms. Pay close attention to any signs of infection, such as a fever or flu-like symptoms.
In most cases, symptoms are mild and last only a few days. However, if symptoms persist and illness does not improve after 5 days, make an appointment with your doctor.
A person should also seek medical help at once if symptoms of listeriosis occur:
- during pregnancy
- in someone with a compromised immune system due to, for example, HIV, diabetes, or chemotherapy
- in a newborn or infant
- in an older adult
Be ready to describe any symptoms to the doctor and give details about the food and when the person ate it.
Treatment for listeriosis depends on how severe your symptoms are and your overall health.
If your symptoms are mild and you are otherwise in good health, treatment may not be necessary. Instead, your doctor may instruct you to stay home and care for yourself with close follow-up.
Home treatment for listeriosis is similar to treatment for any foodborne illness. To treat a mild infection at home, you can:
- Prevent dehydration by drinking water and clear liquids if vomiting or diarrhea occur.
- Use over-the-counter medications to manage body aches and fever, such as acetaminophen (Tylenol) and nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen (Advil or Motrin) or naproxen (Aleve).
- During recovery, eat foods that are easy to process. These include bananas, rice, applesauce, and toast. Limit spicy foods, dairy, alcohol, or fatty foods like meat.
For more severe cases of listeriosis, your doctor will prescribe antibiotics. These are drugs that kill bacteria or slow their growth. Some types of antibiotics that are commonly used for listeriosis include ampicillin and trimethoprim-sulfamethoxazole (Bactrim).
If you have invasive listeriosis, you’ll likely need to stay in the hospital and be treated with intravenous (IV) medications. Antibiotics through an IV can help eliminate the infection, and the hospital staff can watch for complications.
Treatment in pregnancy
If you’re pregnant and have listeriosis, your doctor will want you to begin treatment with antibiotics. They’ll also monitor your baby for signs of distress. Newborn babies with an infection will receive antibiotics as soon as they’re born.
Recovery from a mild infection may be quick and you should feel back to usual within a few days.
If you have a more advanced infection, recovery depends on the severity of the infection. Generally, prompt treatment with an antibiotic can reduce symptoms and help prevent complications.
If your infection becomes invasive, recovery may take longer. You may also need to stay in the hospital during part of your recovery so you can have IV antibiotics and fluids.
A newborn with listeriosis may need antibiotics for several weeks while their body handles the infection. This will likely require the newborn to remain in the hospital. Late onset listeriosis typically has a
Practicing food safety measures is the best way to prevent listeriosis. To do this, follow the tips below:
- Keeping clean. Cleanliness is key. Clean your hands, counters, and appliances. Reduce the possibility of cross-contamination by washing your hands before and after cooking, cleaning produce, or unloading groceries.
- Washing produce thoroughly. Under running water, scrub all fruits and vegetables with a produce brush. It’s best to do this even if you plan to peel the fruit or vegetable.
- Cooking foods well. Kill bacteria by fully cooking meats. Try using a meat thermometer to ensure you’ve reached recommended safe cooking temperatures.
- Avoiding certain foods if you’re pregnant. During pregnancy, limit foods that could be contaminated with Listeria bacteria. Some examples include unpasteurized cheeses, deli and processed meats, or smoked fish.
- Cleaning your fridge regularly. Wash shelves, drawers, and handles with warm water and soap regularly to kill bacteria.
- Keeping temperatures cold enough. Listeria bacteria don’t die in cold temperatures, but a properly cooled fridge can slow bacteria growth. If you can, invest in an appliance thermometer and maintain a refrigerator temperature at or below 40°F (4.4°C). The freezer should be at or below 0°F (-17.8°C).
Listeriosis is a bacterial infection that’s typically transmitted by eating contaminated food. Some examples include soft cheeses, deli meats, and raw fruits and vegetables.
While listeriosis may cause mild illness in healthy people, it can have a serious effect on others. These include pregnant people, older adults, and people with a weakened immune system. Pregnant people can also pass the infection to their baby, leading to serious illness or death.
The best way to prevent listeriosis is to follow good food safety practices when handling, cooking, or eating food. Additionally, those that are at risk of serious illness should aim to avoid foods that are frequently associated with listeriosis.