Pathogens 101 | Listeria

What is Listeria?

Listeriosis is an uncommon but potentially fatal infection usually caused by food contamination. The bacterium Listeria monocytogenes is what causes foodborne illness, and can cause high fever, severe headache, neck stiffness and nausea. It is an important public health problem in the United States.

Healthy people rarely contract listeriosis. Listeriosis can cause miscarriages and stillbirths, as well as serious and sometimes fatal infections in those with weakened immune systems, such as infants, the elderly, and persons living with HIV or undergoing chemotherapy.

What are the Symptoms of Listeriosis?
A person with listeriosis usually has fever and muscle aches, sometimes preceded by diarrhea or other gastrointestinal symptoms. Almost everyone who is diagnosed with listeriosis has “invasive” infection, in which the bacteria spread beyond the gastrointestinal tract.

Symptoms vary with the infected person:

  • Pregnant women: Pregnant women typically experience fever and other non-specific symptoms, such as fatigue and aches.
  • Infections during pregnancy can lead to miscarriage, stillbirth, premature delivery, or life-threatening infection of the newborn.
  • Persons other than pregnant women: Symptoms, in addition to fever and muscle aches, can include headache, stiff neck, confusion, loss of balance, and convulsions.

Manifestations of listeriosis are host-dependent.
Listeriosis can present in different ways depending on the type of infection. In older adults and persons with immunocompromising conditions, septicemia and meningitis are the most common clinical presentations. Pregnant women may experience a fever and other non-specific symptoms, such as fatigue and aches, followed by fetal loss or bacteremia and meningitis in their newborns. Immuno-competent persons may experience acute febrile gastroenteritis or no symptoms. In the United States, an estimated 1,600 persons become seriously ill with listeriosis each year. Of these, 260 die.

How does someone get listeriosis?
You get listeriosis by eating food contaminated with Listeria monocytogenes. Babies can be born with listeriosis if their mothers eat contaminated food during pregnancy. However, healthy persons may consume contaminated foods without becoming ill. Persons at risk can prevent listeriosis by avoiding certain high-risk foods and by handling and storing food properly.

Who Gets Listeriosis?
• Pregnant women: Pregnant women are about 13 times more likely than the general population to get listeriosis. About one in six (17%) cases of listeriosis occurs during pregnancy.
• Newborn babies: Newborn babies suffer the most serious effects of infection in pregnancy.
• Persons with weakened immune systems from transplants or certain diseases, therapies, or medications.
• Persons with cancer, diabetes, alcoholism, liver or kidney disease.
• Persons with AIDS: They are almost 300 times more likely to get listeriosis than people with normal immune systems.
• Older adults
• Healthy children and adults occasionally get infected with Listeria, but they rarely become seriously ill.

Most human infections follow consumption of contaminated food. When Listeria bacteria get into a food processing factory, they can live there for years, sometimes contaminating food products. The bacterium has been found in a variety of raw foods, such as uncooked meats and vegetables, as well as in foods that become contaminated after cooking or processing, such as soft cheeses, processed meats such as hot dogs and deli meat (both products in factory-sealed packages and products sold at deli counters), and smoked seafood. Unpasteurized (raw) milk and cheeses and other foods made from unpasteurized milk are particularly likely to contain the bacterium.

Listeria is killed by pasteurization and cooking; however, in some ready-to-eat foods, such as hot dogs and deli meats, contamination may occur after factory cooking but before packaging. Unlike most bacteria, Listeria can grow and multiply in some foods in the refrigerator.

How do I know if I have Listeriosis?
If you develop fever and chills while pregnant or if you are very sick with fever and muscle aches or stiff neck, consult your doctor immediately. A blood or spinal fluid test (to look for the bacteria) will show if you have listeriosis.

How is Listeriosis Treated?
• Listeriosis is treated with antibiotics. A person in a high-risk category who experiences fever and other non-specific symptoms, such as fatigue and aches, within 2 months of eating contaminated food should seek medical care and tell the physician or health care provider about eating the contaminated food.
• If a person has eaten food contaminated with Listeria and does not have any symptoms, most experts believe that no tests or treatment are needed, even for persons at high risk for listeriosis.

Even with prompt treatment, some listeriosis cases result in death. This is particularly likely in older adults and in persons with other serious medical problems. The CDC listeriosis page:

The following recommendations for persons who are pregnant, immunocompromised (including transplant recipients, individuals with HIV/AIDS, cancer), and older adults, are at higher risk for listeriosis:

• Do not eat hot dogs, luncheon meats, cold cuts, other deli meats (e.g., bologna), or fermented or dry sausages unless they are heated to an internal temperature of 165°F or until steaming hot just before serving.
• Avoid getting fluid from hot dog and lunch meat packages on other foods, utensils, and food preparation surfaces, and wash hands after handling hot dogs, luncheon meats, and deli meats.
• Pay attention to labels. Do not eat refrigerated pâté or meat spreads from a deli or meat counter or from the refrigerated section of a store. Foods that do not need refrigeration, like canned or shelf-stable pâté and meat spreads, are safe to eat. Refrigerate after opening.

• Do not eat soft cheese such as feta, queso blanco, queso fresco, brie, Camembert, blue-veined, or panela (queso panela) unless it is labeled as made with pasteurized milk. Make sure the label says, “MADE WITH PASTEURIZED MILK.”

• Do not eat refrigerated smoked seafood, unless it is contained in a cooked dish, such as a casserole, or unless it is a canned or shelf-stable product.
• Refrigerated smoked seafood, such as salmon, trout, whitefish, cod, tuna, and mackerel, is most often labeled as “nova-style,” “lox,” “kippered,” “smoked,” or “jerky.”
• These fish are typically found in the refrigerator section or sold at seafood and deli counters of grocery stores and delicatessens.
• Canned and shelf stable tuna, salmon, and other fish products are safe to eat.

3 Easy Steps To Help Prevent Listeriosis
The U.S. Food and Drug Administration (FDA), the Centers for Disease Control and Prevention (CDC), and the U.S. Department of Agriculture (USDA) recommend that consumers follow these three easy steps to help prevent listeriosis:
1. Keep the refrigerator at 40°F (4°C) or below.
2. Use ready-to-eat, refrigerated foods as soon as possible.
3. Clean the refrigerator regularly.

It’s All About the Fridge
Keeping the refrigerator at 40°F or below is important because – unlike most foodborne bacteria – Listeria will grow in the refrigerator, and it will grow faster at refrigerator temperatures above 40°F. And, the longer ready-to-eat, refrigerated foods are stored in the refrigerator, the more time Listeria has to grow. Finally, Listeria can spread from one food to another through spills in the refrigerator. That’s why keeping the refrigerator clean is also important!

Who’s At Risk
People with weakened immune systems are not able to effectively fight illness, so listeriosis can be particularly serious for at-risk people. If you’re at risk or if you’re preparing food for someone who’s at risk, read on for the specific things you should know.

→ Here are 3 very specific things you can do to help prevent listeriosis. ←
at the Right Temperature
• Your refrigerator should register at 40°F (4°C) or below and the freezer at 0°F (-18°C).
• Place a refrigerator thermometer in the refrigerator, and check the temperature periodically. Adjust the refrigerator temperature control, if necessary. Place a second thermometer in the freezer.

Ready-to-Eat Foods ASAP!
• Use ready-to-eat, refrigerated foods as soon as possible. The longer they’re stored in the refrigerator, the more chance Listeriahas to grow.

the Refrigerator
• Clean your refrigerator regularly.
• Wipe up spills immediately. This is particularly important, so Listeria doesn’t have a place to grow and then spread to other foods.
• Clean the inside walls and shelves with hot water and a mild liquid dish-washing detergent; then rinse. Then dry with a clean cloth or paper towel.

New Studies
New studies show that Listeria can grow over time at refrigerator temperatures above 40°F (4°C). And, the longer ready-to-eat, refrigerated foods are stored in the refrigerator, the more chance Listeria has to grow.

Through food handling and spills, Listeria in refrigerated food can spread to other non-contaminated foods. The good news is – cleaning the refrigerator will often prevent the spread of Listeria.

Refrigerator Thermometers A Must-Have for Food Safety!
To reduce your risk for listeriosis, it’s important to use an appliance thermometer made specifically for use in a refrigerator or freezer.

For safety, it is important to verify the temperature of refrigerators and freezers. Refrigerators should maintain a temperature no higher than 40°F (4°C). Frozen food will hold its top quality for the longest possible time when the freezer maintains 0°F (-18°C). An appliance thermometer can be kept in the refrigerator and freezer to monitor the temperature.

Two are Better than One!
If possible, buy two appliance thermometers – one for your refrigerator and one for your freezer. The refrigerator should register at 40°F (4°C) or below. The freezer should register at 0°F (-18°C).
• To measure the temperature in the refrigerator: Put the thermometer in the middle of the refrigerator. Wait 5 to 8 hours. If the temperature is greater than 38° to 40°F (3° to 4°C), adjust the refrigerator temperature control to a lower setting. Check again after 5 to 8 hours.
• To measure the temperature in the freezer: Place the thermometer between frozen food packages. Wait 5 to 8 hours. If the temperature is greater than 0 to 2°F (-18° to -17°C), adjust the freezer temperature control to a lower temperature setting. Check again after 5 to 8 hours.


Contact Us

Send us an email and we'll get back to you, asap.

Not readable? Change text. captcha txt

Start typing and press Enter to search