What is Listeria?

What is listeria?

Listeria Monocytogenes is a bacterium that can cause a foodborne illness called listeriosis. The primary groups of people who are affected by listeria are high risk populations including the elderly, pregnant women, young children, and people with weakened immune systems. Every year, an estimated 1,600 people become infected with listeria and roughly 260 die from the contamination. However, most cases of Listeria infection go unnoticed and are not life threatening. The bacterium listeria monocytogenes can be traced back to water, soil, and some animals such as poultry and livestock. The bacterium can also live in food processing factories which means packaged or processed foods are susceptible to contamination. The most common types of foods associated with Listeriosis infections are processed meats and raw milk products. Listeria can reproduce even in extremely cold temperatures inside freezers and must be eliminated through cooking or pasteurization. 

Some foods that have been linked to listeria include:

  • Soft cheeses made with unpasteurized milk
  • Ready to eat meats such as hot dogs
  • Smoked seafood
  • Raw sprout vegetables

Symptoms and Treatment of Listeria

  • Muscle aches
  • Fever
  • Nausea
  • Diarrhea
  • Headache
  • Stiff neck
  • Dizziness

Symptoms for listeriosis typically show up between weeks 1 and 4 from initial infection but there have been cases where infected parties reported illness signs from day 1 all the way to day 70. Doctors diagnose listeriosis by checking for the symptoms listed above and through a series of questions on your previous consumption habits. A blood test can be taken to check for listeria. If the infection is deemed serious enough, antibiotics will be administered to fight off the bacteria. However, most adults who are infected with listeria recover on their own with drinking lots of water and resting.

Prevention of Listeria

If there are ever any listeria outbreaks, keep in mind what you have consumed and if they crossover with any of the listed contaminated foods. For an up to date list of outbreak investigations past and present, visit the official CDC Multi-state Foodborne Outbreaks page.

  • Keep raw meats such as red meat, poultry, and seafood bagged in leak-proof plastic and separate from other food items when shopping.
  • Wash hands thoroughly after visiting the restroom
  • Keep raw meats and raw vegetables separate during preparation to avoid cross contamination
  • Wash raw produce thoroughly before cooking. Animal fecal matter used in soil fertilization might have the listeria bacterium.
  • Consume ready to eat foods as soon as possible
  • Do not consume suspicious smelling or looking food

Pregnant Women, Newborns, and Listeria

Pregnant women are advised to closely monitor their diets to avoid foods that may carry Listeria Monocytogenes. Although the disease is rare even among pregnant women, the consequences for fetuses may be severe. Pregnant women are ten times more susceptible to listeriosis than individuals of the healthy adult population and symptoms are often non life-threatening but may lead to miscarriage, premature labor, or permanent damage to a baby. One such illness is called granulomatosis infantiseptica and causes disorders in internal organs and the skin of the baby. Infected pregnant women can take antibiotics to prevent spreading the illness to her baby and infected babies can be treated by the same method. For the protection of unborn children, follow the suggested guidelines during pregnancy:

  • Avoid processed meats such as deli meat, hot dogs, and luncheon meat unless they are heated thoroughly
  • Avoid refrigerated pates or meat-based spreads
  • Avoid raw milk and raw milk products such as soft cheeses
  • Do not eat cold-served smoked seafood
  • No cold, store-bought salads

Listeria Outbreaks

Recent listeria outbreaks are listed below:


Vulto Creamery Soft Raw Milk Cheese

  • Six people have been infected with a strain of Listeria that has been traced back to samples of Ouleout cheese from the Vulto Creamery
  • Six out of six of the identified infected persons stated they had consumed soft cheeses months prior to the illness showing signs
  • On March 7, 2017, Vulto Creamery recalled 4 different cheeses and 3 days later recalled4 more types of cheese to include Heinennellie, Miranda, Willowemoc, Ouleout, Andes, Blue Blais, Hamden, and Walton Umber
  • Of the six infected individuals, two have died and they resided in Connecticut and Vermont
  • The cheese were distributed to retail locations all across the U.S.
  • This outbreak investigation is ongoing


Frozen Vegetables

  • 11 vegetable products from CRF Frozen Foods of Pasco, Washington were distributed to multiple states.
  • 9 people were infected in 4 different states with 3 of those 9 individuals dying.

Raw Milk

  • Raw milk linked to Miller’s Organic Farm in Bird-In-Hand, Pennsylvania led to the infection of two individuals in California and Florida. The listeria infection led to one death.
  • Although the illnesses occurred in 2014, the CDC did not find the source of the listeria outbreak until two years later.

To learn more about other foodborne illnesses, visit the main foodborne illness page.