Listeriosis is a serious illness most often caused by eating food contaminated with Listeria monocytogenes, bacteria that are commonly found in the environment in soil, decaying vegetation, water, animals, and humans. Pregnant women and their newborns, adults aged over 65, and people with weakened immune systems are most at risk for becoming ill with listeriosis.

How is listeriosis spread?

Foods that are more likely to be contaminated with Listeria bacteria include raw (unpasteurized) milk, soft cheeses, raw vegetables, melons, and ready-to-eat meats such as hot dogs, pâté, and deli meats. The bacteria can also be transferred from one food to another by improper food handling. Listeria can grow in refrigerated foods.

Listeria is rarely spread directly from person to person but may be spread from an ill pregnant woman to her unborn or newborn baby.

What are the symptoms of listeriosis?

People become ill a few days to as long as over two months after consuming contaminated food. Symptoms include fever, diarrhea, muscle aches, headache, nausea and vomiting, and generally feeling unwell. Serious and sometimes fatal complications can occur when the infection spreads to the blood or affects the brain or heart.

Pregnant women may experience only a mild, flu-like illness. However, infections during pregnancy can lead to miscarriage, stillbirth, premature delivery, or life-threatening infection of the newborn.

What is the treatment for listeriosis?

In general, people with mild illness only require rest and fluids, to replace what is lost through diarrhea. People with severe symptoms or symptoms that last a long time, pregnant women and their newborns, adults aged over 65, and people with weakened immune systems should seek care from their health care provider. Doctors test a patient’s blood to detect Listeria.

How can I protect myself against listeriosis?

Persons at highest risk for severe illness (such as pregnant women, adults aged over 65, and people with weakened immune systems), should avoid high risk foods, such as:

  • raw (unpasteurized) milk and cheeses, including soft and semi-soft cheeses such as feta, brie, camembert and blue veined cheeses
  • certain cheeses made from pasteurized milk such as queso fresco and queso blanco as they may become contaminated during the making of the cheese
  • ready-to-eat meats such as hot dogs, pâté, deli meats, smoked seafood and fish unless they are heated to an internal temperature of 74°C /165°F or until steaming hot just before serving
  • raw or undercooked forms of meat, poultry and fish such as sushi, sashimi, kibbeh and tartare
  • raw or lightly cooked sprouts of any kind (including alfalfa, clover, radish, and mung bean sprouts)

To prevent becoming ill:

  • Wash fruits and vegetables thoroughly with clean running water. Eat cut melon right away or store in refrigerator no longer than 7 days.
  • Wash, rinse and sanitize all utensils, cutting boards and food preparation surfaces before and after using them.
  • Use separate utensils, cutting boards and food preparation surfaces when preparing raw and cooked foods.
  • Avoid spreading juices from the packaging of processed meats, such as hot dogs, deli and luncheon meats on other foods, utensils, and food preparation surfaces. Be sure to wash your hands after handling these food products.
  • Heat ready-to-eat foods thoroughly.
  • Store opened packages of hot dogs no longer than 1 week in the refrigerator and unopened packages no longer than 2 weeks in the refrigerator.
  • Store factory-sealed, unopened packages of lunch and deli meat no longer than 2 weeks in the refrigerator.
  • Store opened packages and meat sliced at a local deli no longer than 3 to 4 days in the refrigerator.
  • Check and use food packaging labels as instructed. Store perishable foods, such as raw meats and fresh fruits and vegetables, in the refrigerator at 4°C/40°F or lower.
  • Do not eat food items that have been recalled. These items should be discarded or returned to the location of purchase.
  • Purchase milk and other dairy products that are pasteurized. For cheeses and other dairy products, make sure the label says, “made with pasteurized milk.”
  • Always wash hands well with soap and water for at least 15 seconds before and after preparing food, before eating, after using the toilet, after changing diapers, after handling pets or their feces, and any time hands may be dirty.
What should I do if I may have eaten food contaminated with Listeria?

Those who believe they may have eaten food contaminated with Listeria and have symptoms of possible listeriosis infection within two months after eating the food item should seek medical care. This is especially important for those who are pregnant, over 65 years, or have a weakened immune system.

What is Ottawa Public Health’s role?

Ottawa Public Health (OPH) must be notified by health care providers and laboratories when a person is ill with listeriosis. OPH conducts an investigation to potentially determine the cause or source of the infection, provides education to the ill person, and follows up with health care providers as needed.

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