What is listeria? Everything you need to know

This illustration depicts a three-dimensional (3D) computer-generated image of a grouping of Listeria monocytogenes bacteria. The artistic recreation was based upon scanning electron microscopic (SEM) imagery.

(CNN)Listeria is back in the news again after packages of butternut squash, cauliflower, zucchini and butternut squash based vegetable bowl products from brands Trader Joe's, Green Giant and Signature Farms were recalled.

The manufacturer of the products, Growers Express, voluntarily recalled the products after concerns about a possible contamination of the potentially fatal bacteria Listeria monocytogenes.
"Listeria is an organism that can cause serious and sometimes fatal infections in young children, frail or elderly people, and others with weakened immune systems," the US Food and Drug Administration said in a statement. "Although healthy individuals may suffer short-term symptoms such as high fever, severe headaches, stiffness, nausea, abdominal pain and diarrhea. Listeria infection can cause miscarriages and stillbirths among pregnant women."
Here's what you need to know about the bacteria, and what happens if you get it:

    What is it?

    Listeria monocytogenes is a hardy bacterium that is resistant to extreme hot and cold. This bacterium is pathogenic -- meaning that it is infectious to humans, causing the illness listeriosis.

    Where does it come from?

    Listeria is found in soil, water and the intestines of some animals. But most animals who have it show no symptoms, so the bacterium can get transferred to raw foods such as unpasteurized dairy products, raw vegetables and raw meats.
    But unlike other types of bacteria, Listeria can still grow in the low temperatures of a refrigerator. And when Listeria gets into a factory environment, it can live for several years, the U.S. Food and Drug Administration says.
    Studies suggest that up to 10% of humans may be carriers.

    Who is most at risk?

    Listeriosis primarily affects the elderly, pregnant women, newborns and people with weakened immune systems. In the U.S., an estimated 1,600 people become seriously ill each year. And about 16% of those illnesses result in death.
    Cervical infections caused by listeriosis in pregnant women may result in spontaneous abortion during the second or third trimesters or stillbirth.

    What are the symptoms of listeriosis?

    The early symptoms of listeriosis are similar to those of the flu with nausea, muscle aches and a high fever. Gastrointestinal symptoms such as diarrhea may also appear.
    But the length of time between infection and the appearance of symptoms is unknown.

    How can I protect myself?

    Recommendations for keeping food safe from Listeria are similar to those used to protect against other foodborne illnesses. Remember to cook meat to the USDA's recommended temperatures and to wash all raw vegetables and fruit.
    Keep your fridge below 40 degrees Fahrenheit, and eat leftovers within three to four days, the Centers for Disease Control and Prevention says.

    How common is Listeria infection?

    About 800 cases of Listeria infection are diagnosed each year in the United States, along with three or four outbreaks of Listeria-associated foodborne illness.
      A multi-state outbreak of Listeria from contaminated hot dogs and deli meats occurred in 1998, killing 21.
      Between 1998 and June 2009, 48 deaths from Listeria-caused illnesses were reported by the CDC's Foodborne Outbreak Online Database.
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