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Listeriosis is an uncommon bacterial infection caused by the bacteria Listeria monocytogenes. This bacterium is widespread in nature and most cases are sporadic, although food borne outbreaks and person-to-person spread have been documented. L. monocytogenes is most commonly found in the soil, water, mud, cattle forage, and silage. Infected humans and animals can also shed the bacteria.

Listeriosis is reportable to the Iowa Department of Public Health by Iowa Administrative Code 641 Chapter 1.


Symptoms can occur anywhere from 3 to70 days after exposure, but the average incubation period is about three weeks. Infection may result in acute, mild illness with fever or may be more severe and result in infection of the brain causing the following signs:

  • Sudden fever
  • Intense headache
  • Nausea and vomiting
  • Diarrhea
  • Delirium
  • Coma

Infection in the heart muscle or lesions in the liver or skin have also been reported. Spontaneous abortion in pregnant women is also possible.


Listeriosis is caused by eating food contaminated with the bacterium. L. monocytogenes, which can be found in soil, water, and animals. L. monocytogenes can multiply at refrigerator temperatures unlike most other food borne pathogens. Most cases of Listeriosis are associated with the consumption of raw milk, soft cheeses, ready-to-eat foods, processed meats, or contaminated vegetables. Infected individuals may shed the bacteria in their urine and feces but human-to-human transmission is uncommon. Listeriosis may be acquired by the fetus in utero or during passage through the birth canal. Mothers can shed the bacteria in their vaginal secretions and urine for up to 10 days after delivery and newborns may become infected before birth or as they pass through the birth canal.

Risk Factors

Immunosuppressed individuals such as newborns, the elderly, and pregnant women are at an increased risk for Listeriosis. Approximately 30 percent of diagnosed cases occur within the first three weeks of life. The case-fatality rate in infected newborn infants is about 30 percent and approaches 50 percent when onset occurs in the first four days of life.


Prevention recommendations for high risk individuals, including those that are immunosuppressed, are as follows:

  • Avoid unpasteurized milk and soft cheeses such as feta, Brie and blue cheese
  • Thoroughly heat leftover foods or ready-to-eat foods such as hot dogs or processed lunch meats before eating
  • Avoid foods from delicatessen counters or thoroughly re-heat cold cuts before eating

Prevention recommendations for all individuals include the following:

  • Keep uncooked meats separate from vegetables, cooked food, and ready-to-eat foods
  • Avoid raw/unpasteurized milk or foods made from raw milk
  • Thoroughly wash raw vegetables before eating
  • Wash hands, knives, and cutting boards after handling uncooked foods
  • Read and follow label instructions to “keep refrigerated” and “use by” a certain date

Because this bacterium can be shed in the feces of infected individuals, people with diarrhea (especially children in child care settings or people who handle food) should not go to school or work. Individuals may usually return when their diarrhea stops if they carefully wash their hands after using the toilet, diapering, and before and after handling food.


Listeriosis is treated with antibiotics. Severe infections may result in hospitalization and require intravenous antibiotic administration, especially for immunosuppressed individuals.


There were three cases of Listeria monocytogenes reported in 2021. 

For more detailed information and statistics on all notifiable diseases, please see our current annual report located in the reports section of the CADE homepage.

Additional Resources