listeria
Listeria is a bacterium that is commonly found in soil and water, which may contaminate the following foods.

Foods that contain Listeria include the following:

  • All animals’ meat, while still uncooked or undercooked
  • Well-cooked ready-to-eat foods such as deli meats and hot dogs (while they undergo other processes such as slicing)
  • Raw fish and shellfish
  • Raw eggs
  • Raw unpasteurized milk
  • Cheese made from raw milk
  • Unpasteurized dairy products
  • Cream or custard
  • Unwashed raw vegetables and fruits
  • Uncooked pre-prepared foods such as sushi and sandwiches
  • Other ready to eat foods
  • Hummus and other dips that contain tahini
  • Cold-cut meats
  • Refrigerated meat pâté or spread
  • Refrigerated smoked fish
  • Soft serve ice-cream

How is food contaminated with Listeria?

Listeria bacterium, especially Listeria monocytogenes, can be found in soil and water.

  • Vegetables and fruits can be polluted by soil or manure used as fertilizer.
  • Animals can carry the germs without becoming unwell, and meat or dairy products derived from these animals can become infected.
  • Bacteria have been detected in raw foods such as uncooked meats and vegetables, as well as processed goods that have become contaminated during processing, such as cheese and cold cuts at the deli counter.
  • The bacterium may be present in unpasteurized (raw) milk or foods produced from raw milk.
  • Listeria can infect other foods in the refrigerator through spillage, especially juices from the following:
    • Hot dog
    • Lunchmeat packages
    • Raw meat
    • Raw poultry

What is Listeria?

Listeria is a bacterium that is commonly found in soil, water, and refrigerators and even on your hands.

  • Among all other species of Listeria, Listeria monocytogenes is the most predominant and highly virulent, which means it causes a serious infection that may even lead to death.
  • Consumption of food contaminated with Listeria causes food poisoning.
  • Listeriosis is an infection caused by the Listeria bacterium that leads to food poisoning.
Each year, about 1,850 people in the United States become very ill with listeriosis, out of which about 425 of them are killed.

Who are at a risk of listeriosis?

Although Listeria is present almost everywhere in your environment, your immune system fights off bacteria and prevents infection in your body from listeriosis (an uncommon infection).

Although healthy adults and children ingest Listeria-infected food, they do not become ill, but people who are prone to the disease will almost certainly become ill after they consume even a few bacteria.

The following people are more prone to listeriosis:

  • People with weak immune systems, especially:
    • Due to an infection such as human immunodeficiency virus infection where the immune system is disrupted.
    • After taking immunosuppressants as a treatment of other medical conditions such as kidney or liver diseases and cancer
  • Women who are pregnant and their unborn fetus and newborns:
    • Pregnant women have weak immunity
    • Listeria can transmit from the mother to her baby during pregnancy through the placenta (vertical transmission)
    • Although it is believed that the mother may transmit Listeria through her breast milk, there is no strong evidence to support the statement
  • People who are 65 years and older and who may have a weak immune system due to aging

SLIDESHOW

Bacterial Infections 101: Types, Symptoms, and Treatments See Slideshow

What are the symptoms of listeriosis?

The incubation period—the time from being infected with the bacterium to the appearance of the first symptoms of Listeria monocytogenes—may range from four days to several weeks, which may go up to 70 days. Listeria that spreads to other parts such as the brain and placenta from the gut have longer incubation periods.

The most common symptoms of listeriosis may include:

Serious illness may cause the following:

How is listeriosis diagnosed?

Symptoms caused by Listeria bacterium, especially the most common symptoms, give the doctor a picture of possible food poisoning. However, to know the exact organism that caused food poisoning, bacterial culture has to be done.

Some body tissue such as the placenta or body fluids such as the blood and spinal fluid are collected and cultured in a lab to find the causative organism. After a while, bacteria that are grown on the culture media are studied under the microscope to identify the organism.

What are the treatment options for listeriosis?

If you are diagnosed with listeriosis, your doctor will prescribe you antibiotics to treat listeriosis. Early detection and treatment of Listeria in pregnant women is a must because they prevent the transmission of infection to the baby. Infected babies may be treated with antibiotics in appropriate doses.

However, even with quick treatment, some infections result in mortality. This is more likely among the elderly and people who have other major medical concerns.

How to prevent listeriosis

Avoiding high-risk foods and using hygienic food-handling procedures are the best ways to avoid Listeria infection.

  • If you're going to cook something, cook it well.
  • Before you consume fresh raw fruits and veggies, make sure to thoroughly wash them first.
  • Cookware and utensils should be thoroughly cleaned.
  • After handling raw foods, wash knives and cutting boards.
  • Refrigerate raw items at the bottom of the fridge and check the temperature regularly.
  • Refrigerate any leftovers right away. Throw them out if you don't eat them within 24 hours.
  • If you do reheat them, make sure they're hot and steaming.
  • Refrigerate frozen meats to thaw.
  • Keep raw meat separate from vegetables, cooked foods, and ready-to-eat items in the fridge and while preparing food.
  • Scrub the surface of melons such as cantaloupes, watermelon, or honeydew before cutting, and wash hands for 20 seconds before and after handling with warm water and soap.
  • Direct contact with infected animals can lead to infection in veterinarians, farmers, and others who care with animals, so take precautions.

High-risk people and pregnant women should follow the suggested recommendations:

  • It is not necessary to eliminate hard cheese, processed cheese, cream cheese, cottage cheese, or yogurt, but you should avoid soft cheese, such as:
    • Feta
    • Brie
    • Camembert
    • Blue-veined 
    • Mexican-style cheese
  • Cook leftovers or ready-to-eat meals such as hot dogs until they are steaming hot before eating.
  • Although the risk of listeriosis from deli counter foods is generally low, pregnant women and others with impaired immune systems may choose to avoid these meals or completely reheat cold cuts before consuming.

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Medically Reviewed on 2/15/2022
References
Image Source: iStock Images

Listeria (Listeriosis): https://www.cdc.gov/listeria/index.html

How does Listeria get into food? https://ask.usda.gov/s/article/How-does-Listeria-get-into-food

Listeria Infection (Listeriosis): https://mothertobaby.org/fact-sheets/listeriosis-pregnancy/

Listeriosis: http://www.idph.state.il.us/public/hb/hblister.htm