What’s the Buzz

What is a Listeria Outbreak and What Does It Mean?

Cartoon box filled with food, someone using a magnifying glass to inspect.

Listeria outbreaks have been featured in the news after the Centers for Disease Control and Prevention (CDC) issued a food safety alert for Big Olaf Creamery, an ice cream brand sold in Florida. Please continue reading to find out what is a listeria outbreak, who is at risk, and how you can prevent it.

What is Listeria and what does it do to you?

Listeria is an infection that occurs from eating food contaminated by a harmful bacteria called Listeria monocytogenes. This bacteria causes a foodborne illness called listeriosis. Listeria monocytogenes is commonly found in groundwater, soil, animal feces, and rotting vegetation.

Most people with healthy immune systems do not become ill from eating contaminated foods that contain Listeria bacteria. However, some people are at high risk of developing listeriosis. People at risk of serious infection and severe symptoms include pregnant women, newborn babies, older adults aged 65 years and above, and people with weakened immune systems due to cancer treatments, AIDS, immunosuppressive drugs, or other reasons.

After eating contaminated food, Listeria bacteria can spread from the gut to other parts of the body. This is a potentially life-threatening infection called invasive listeriosis. It can cause brain or blood infection and lead to lifelong health problems or even death. 

What makes Listeria bacteria unique?

The bacteria Listeria monocytogenes is unique in two ways. One, this bacteria can survive inside the cells and grow even at very low temperatures, including freezing and refrigeration temperatures. 

Two, whereas contaminated food typically develops an unpleasant taste, smell, or texture, food contaminated with the bacterium Listeria monocytogenes does not undergo any changes in taste, smell, or texture that can alert you to spoiled food.

What is a Listeria outbreak?

As mentioned above, people who eat foods contaminated with Listeria bacteria can develop a severe illness. Listeriosis outbreaks occur when a batch of commercially sold food products becomes contaminated with Listeria bacteria. 

If contamination of a food product with Listeria monocytogenes is identified, the CDC will issue a food safety alert advising consumers to throw away any remaining product and to clean any containers, utensils, and food preparation surfaces that came in contact with the contaminated food product.

Are Listeria outbreaks common?

Listeria outbreaks are relatively rare. Approximately 1,600 people are diagnosed with listeriosis in the US each year. However, this infection can be fatal. More than 250 people die from Listeria infections every year. 

What causes a Listeria outbreak?

Listeria infection is most commonly caused by contaminated ready-to-eat foods, such as:

  • Deli meat that hasn’t been properly processed 
  • Unpasteurized milk products 
  • Soft cheeses and Mexican-style cheeses
  • Hot dogs
  • Fresh vegetables and fresh fruits (especially melons) that haven’t been properly washed
  • Raw sprouts or lightly cooked sprouts

While the above-listed high-risk foods are the most common culprits, any food that is improperly handled or prepared can become contaminated.

What are the symptoms of listeriosis infection? How soon do they develop?

The time period between consuming food contaminated with L. monocytogenes and the appearance of symptoms of listeriosis can range from a couple of days to 3 months. Symptoms typically appear 1-2 weeks after you have eaten contaminated food. They include flu-like symptoms such as fever, chills, nausea, diarrhea, and muscle aches. 

If the listeria infection spreads beyond the gut to the nervous system, it can lead to a serious illness with additional signs and symptoms such as headache, stiff neck, confusion, reduced alertness, balance problems, and convulsions.

Is listeriosis contagious?

No, listeriosis does not spread from person to person. However, unborn babies can contract a Listeria infection from their mother.

How do doctors diagnose listeriosis?

Healthcare providers diagnose listeriosis based on symptoms and medical tests, such as checking food, vomit, blood, and CSF (clear fluid in the brain and spinal cord) for the presence of the bacteria L. monocytogenes. 

Is Listeria infection curable?

Yes, Listeria infections can be treated and cured with antibiotics such as ampicillin (Principen®) and sulfamethoxazole (Bacter-Aid DS®). 

Doctors are more likely to prescribe antibiotics to older adults, pregnant women, newborn babies, and people with a weakened immune system who are at high risk of developing severe listeriosis. Most people feel better after 3-5 days of antibiotic treatment. It’s important to finish the full course of antibiotics even if you are feeling better. 

Healthcare providers may also prescribe additional medications such as antiemetics and nonsteroidal anti-inflammatory drugs to treat symptoms such as nausea, vomiting, fever, and muscle aches. 

Healthy adults with a mild illness may not need any treatment for a Listeria infection. Healthcare providers recommend getting plenty of rest, drinking lots of fluids, and eating a light diet for mild symptoms. 

How can I reduce my risk of contracting a Listeria infection?

As mentioned above, healthy people have a low risk of developing listeriosis. However, those with risk factors such as a weakened immune system, older adults, and pregnant women should take precautions while eating and drinking certain foods as well as storing and preparing food. These precautions can also protect you against other foodborne illnesses.

  • Wash your hands well and clean food surfaces before and after cooking.
  • Consume only pasteurized milk and milk products. Avoid raw milk and unpasteurized dairy products.
  • Clean fresh fruits and vegetables with a scrub brush under running water.
  • Cook eggs, seafood, hot dogs, and deli meats well. Use a food thermometer to ensure the inside temperature is at least 165 degrees F (74 degrees C). 
  • Avoid refrigerated meat spreads pâtés or pureed meat and refrigerated smoked seafood. Canned foods that don’t need to be refrigerated are safe but should be refrigerated after opening and consumed by the use-by date. 
  • Heat leftovers until they are steaming hot. Don’t eat leftovers that are several days old.
  • Wrap food properly in aluminum foil, cling wrap, or plastic bags—store food in clean, covered containers in the refrigerator. 
  • Don’t allow raw meat to leak juices onto other foods. Clean any spills in your refrigerator immediately.


  1. https://www.mayoclinic.org/diseases-conditions/listeria-infection/symptoms-causes/syc-20355269
  2. https://my.clevelandclinic.org/health/diseases/17721-listeriosis
  3. https://www.cdc.gov/listeria/outbreaks/monocytogenes-06-22/index.html