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Listeriosis and Pregnancy

What is Listeriosis? Listeriosis is the name of an infection caused by eating food contaminated with a bacterium called Listeria monocytogenes. These bacteria are found everywhere in the environment. It is commonly found in soil, decaying vegetation and water. People and animals can be carriers of listeria bacteria and never get sick.

Outbreaks of listeriosis have been caused by consuming unpasteurized (raw) milk, soft cheese, vegetables and ready-to-eat meats (like lunch meat).


  • Front of Listeriosis and Pregnancy fact sheetListeriosis and Pregnancy Fact Sheet (PDF 245KB)
    View, download and print the Listeriosis and Pregnancy Fact Sheet. Listeriosis is the name of an infection caused by eating food contaminated with a bacterium called Listeria monocytogenes.

Contact Us

For more information, please contact the Infectious Disease Control Team:

  • 519-663-5317 Ext. 2330

What are the signs and symptoms of listeriosis?

  • Healthy adults sometimes become infected but the illness is usually mild and no treatment is needed. Symptoms of listeriosis in healthy people can include fever, muscle aches, nausea and/or diarrhea.
  • Symptoms usually develop 3 to 70 days (commonly three weeks) after eating food contaminated with the bacteria.
  • Pregnant women experience the same mild illness as healthy adults, but the infection may affect the baby, leading to premature delivery, stillbirth or infection of the newborn.
  • The bacteria can be transmitted from mother to developing baby while pregnant or at delivery from an infected birth canal.

Pregnant woman should seek medical attention if they develop symptoms of listeriosis infection.

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How is listeriosis diagnosed?

A blood test is the most common test to diagnose listeriosis. Testing is only recommended if you are sick with symptoms of listeria, regardless of if you have eaten food that may have been contaminated.

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Is there treatment?

Listeriosis is treated with antibiotics. Prompt treatment of pregnant women with symptoms of listeriosis can prevent infection in the baby. Antibiotic treatment is not recommended if you do not have symptoms.

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How do I prevent infection?

Safe food handling is important in the prevention of foodborne illness like listeriosis. In addition to general safe food handling recommendations, pregnant women are advised to avoid certain foods to reduce the risk of becoming infected with listeriosis:

  • Only eat hot dogs, luncheon meats or deli meats that have been reheated until steaming hot (74ºC). Make sure fluid from hot dog packages does not get on other foods, utensils and food preparation surfaces. Wash hands after touching hot dogs, luncheon meats and deli meats.
  • Avoid soft cheeses such as feta, Brie and Camembert; blue-veined cheeses; or Mexican-style cheeses such as queso blanco, queso fresco and panela.
  • Avoid refrigerated pâtés or meat spreads. Canned or shelf-stable pâtés and meat spreads may be eaten.
  • Avoid refrigerated smoked seafood unless it is used in a cooked dish, such as a casserole. Refrigerated smoked seafood, such as salmon, trout, whitefish, cod, tuna or mackerel, is most often labeled as "nova-style," "lox," "kippered," "smoked" or "jerky." The fish is found in the refrigerator section or sold at deli counters of grocery stores and delicatessens. Canned or shelf-stable smoked seafood may be eaten.

Food that is contaminated with listeria bacteria does not look or smell bad.

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Date of creation: December 29, 2012
Last modified on: November 11, 2016


1Heymann, D.L. (2015). Control of communicable diseases manual (20th ed.). Washington, DC: American Public Health Association.
2Centers for Disease Control and Prevention. Listeriosis. Retrieved from
3Public Health Ontario. Listeriosis. Retrieved November 8, 2016, from Retrieved from