Listeria Infection (Listeriosis)

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Listeriosis is an illness caused by the bacteria Listeria monocytogenes.


Listeriosis is transmitted primarily through ingestion of contaminated food. Transmission also occurs in utero from mother to fetus. 
People most at risk of infection include individuals with weakened immune systems, the elderly and pregnant women. 


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. 
The symptoms vary with the infected person. 

Symptoms for pregnant women can be non-specific and include:

  • Fever
  • Fatigue
  • Body aches

Infection during the pregnancy can cause the following:

  • Stillbirth
  • Miscarriage
  • Premature delivery
  • Bacteremia and meningitis in the newborn  

Symptoms in non-pregnant individuals include:

  • Fever
  • Muscle aches
  • Headaches
  • Stiff neck
  • Confusion and loss of balance
  • Weakness
  • Sometimes vomiting and diarrhea
  • Convulsion

The incubation period from the ingestion of a contaminated food to symptom onset can range from 1 day up to 70 days.    


General recommendations for avoiding Listeriosis - Food handling:  

  • Rinse all raw fruits and vegetables with fresh water before eating, cutting or cooking (including those that will be peeled)
  • Fresh produce with a thick outer layer should be scrubbed with a clean brush during washing (for example fruits such as melons and apples, and vegetables such as cucumbers and potatoes)
  • Dry wash produce with a clean cloth or paper towels prior to use
  • Keep all raw/uncooked meat, fish and poultry separate from fruit, vegetables, cooked foods and ready-to-eat foods 

Kitchen safety:

  • Wash hands, knives, utensils, cutting boards, kitchen surfaces and other materials used when preparing raw food products (including meat, dairy, vegetables and fruit)
  • Ensure you refrigerator is at 40°F or lower and freezer 0°F or lower to avoid the bacteria from growing
  • Routinely clean the inside walls and shelves of the refrigerator and immediately clean any spills involving high risk foods – use hot soapy water and then rinse

Food Storage and preparation safety:

Cook all raw food from an animal origin to the appropriate internal temperature -

  • Check and adhere to the used-by dates on ready-to-eat foods
  • Eat any unlabeled/unpackaged deli items, such as sliced deli meats, salads and smoked fish the day of purchase or within 2 days
  • Re-heat any leftover cold deli meats, pre-cooked meats or food, hot dogs and smoked seafood prior to consumption and dispose of leftovers within 2 days
  • Eat all cooked and pre-cooked seafood products when hot, do not keep leftovers
  • Home- or pre-cooked meat, such as rotisserie chicken, should be eaten when first cooked and hot or thoroughly re-heated and eaten within 2 days
  • High risk foods at room temperature –  
    • Up to 2 hours – can be returned to the refrigerator (to be re-heated) 
    • Between 2 to 4 hours – must be eaten immediately
    • More than 4 hours – dispose of all product

Recommendations for high-risk groups (Pregnant women, elderly and those with weakened immune systems) Soft Cheese:

  • Avoid eating soft cheeses unless they are made with pasteurized milk, including – queso fresco (be aware many pasteurized Mexican-style cheeses have been responsible for cases of Listeriosis and are likely contaminated during the cheese making process), Brie, Camembert, blue-veined cheese, queso panela and feta


  • Avoid eating deli/lunch meats, cold cuts, hot dogs and fermented or dry sausages (ready-to-eat meats) unless they have been heated to 165°F or steaming hot before consumption
  • Avoid eating refrigerated or deli-bought meat spreads or pâtés. Canned/shelf stable meat spreads or pâtés are safe to eat but must be refrigerated after opening
  • Wash hands when handling and ensure all fluids from ready-to-eat meat packaging does not contaminate surfaces, utensils or other food


  • Avoid eating any refrigerated smoked seafood products, often labeled as nova-style, lox, kippered, smoked or jerky (including salmon, whitefish, trout, mackerel, cod, tuna, shellfish)
  • Avoid eating any smoked seafood unless it has been thoroughly cooked before consumption or has originated from a can/shelf-stable product (commercial bought only)


There is no vaccine for listeriosis.

Recent Texas Trends

Over the last ten years, 2011-2020, the average number of cases of listeriosis reported in Texas has been 40 cases per year (ranging from 19 to 65). Many cases have been attributed to high-risk foods listed above. Recent outbreaks of listeriosis, involving cases in Texas, have been associated with Mexican-style cheeses such as queso fresco, diced celery, whole cantaloupe, caramel apples, and ice cream products.