Listeria (listeriosis): Spread, prevention and risks
On this page
- How Listeria spreads
- Preventing listeriosis
- Risks of getting listeriosis
- Who is most at risk
- Risks of complications
How Listeria spreads
Listeria can be spread:
- when eating food or drinking water that has been contaminated with the bacteria
- during pregnancy through the placenta from the pregnant parent to the unborn baby
- directly to the newborn during delivery
Listeria can be spread between foods if you don't follow safe food handling practices.
Though rarely reported, it can also be spread by contact with infected animals. For example, farmers, veterinarians and other people who interact with animals can be exposed to Listeria when:
- they help infected animals give birth
- an infected animal is butchered for meat
Generally, Listeria isn't spread between people in the community. The risk of spreading the bacteria to a newborn baby during breastfeeding is also considered to be low.
Where Listeria bacteria are found
Listeria is commonly found in the environment, for example, in soil, sewage and untreated water.
It can also be found in foods such as:
- seafood and fish
- meat and poultry
- fruits and vegetables
- dairy products, such as milk and cheese
- non-dairy, plant-based products and beverages
However, some foods are at a higher risk of being contaminated than others. This depends on factors such as whether the foods:
- are raw or unpasteurized
- are refrigerated and don't need to be heated before eating
- come into contact with many different surfaces during production
- have high-moisture content and low acidity, that support growth of the bacteria
How food and water becomes contaminated
Since Listeria exists naturally in the environment (for example, in soil, in untreated water, and in animals that appear healthy), it can spread to food.
Listeria can contaminate facilities where food is processed and manufactured. Once it enters a facility, it's difficult to eliminate it completely. If it persists on surfaces and equipment, it can contaminate any of the foods that are manufactured there. Furthermore, it can grow at lower temperatures than other bacteria, such as in the refrigerator. As a result, some refrigerated prepared foods are at a higher risk of becoming contaminated with Listeria.
Preventing listeriosis
There's no vaccine to prevent listeriosis.
You can reduce your risk of infection with Listeria by:
- following general food safety tips
- Unlike most bacteria, Listeria can survive and sometimes grow on foods stored in the refrigerator.
- Set your refrigerator at 4°C (40°F) or lower to help slow its growth.
- Set your freezer at -18°C (0°F) or lower to prevent its growth.
- You can kill Listeria by cooking food properly.
- Unlike most bacteria, Listeria can survive and sometimes grow on foods stored in the refrigerator.
- cleaning anything that comes into contact with food, including your hands and kitchen surfaces
- using separate equipment and utensils for handling raw foods and cooked or ready-to-eat foods, to avoid cross-contamination
You can't tell if a food is contaminated with Listeria based on how it looks, smells or tastes. This is why people at high-risk for severe illness can lower their chances of getting sick by avoiding eating certain foods and making safer food choices.
You can help prevent others from getting sick by contacting your local public health authority to report:
- unclean restaurants or grocery stores
- suspected food poisoning from a restaurant
Learn more:
Risks of getting listeriosis
In recent years, about 168 cases of invasive listeriosis were reported annually in Canada. While listeriosis is a rare disease in Canada, certain foods are more likely to carry Listeria than others. Some higher-risk foods include:
- ready-to-eat meats, such as:
- hot dogs
- non-dried deli meats (for example, bologna, roast beef, and turkey breast)
- refrigerated pâtés and meat spreads
- raw or undercooked meat, poultry and seafood
- refrigerated smoked fish
- raw or unpasteurized milk
- soft, semi-soft and blue-veined cheeses
- frozen packaged vegetables that aren't cooked according to their package directions before being eaten
Who is most at risk
Anyone can be infected by Listeria but those who are most at risk of becoming sick with invasive listeriosis include:
- people with weakened immune systems that can't easily fight infections
- adults ages 60 and over
- due to an immune system that weakens with age
- people who are pregnant including their unborn baby and newborns
- due to the parent's immune system that weakens during pregnancy, and the risk of spread through the placenta
- due to a baby's immune system that isn't developed enough to fight off harmful bacteria
Risks of complications
Invasive listeriosis is a rare, but severe, illness that occurs when bacteria in the intestines spread to other areas of the body, such as the:
- bloodstream or
- nervous system (the brain, spinal cord and nerves)
Invasive listeriosis can cause long-lasting health effects and can be fatal.
During pregnancy, both you and your unborn baby are at an increased risk for listeriosis. If you have a Listeria infection, there's an increased risk that your baby could be infected as Listeria can:
- pass through the placenta or
- infect your baby during delivery
Listeriosis can be more serious for the unborn or newborn baby than for the pregnant parent.
Listeria infections during pregnancy can lead to:
- miscarriage
- the death of a fetus in the womb during the first 20 weeks of pregnancy
- stillbirth
- the death of a fetus in the womb (before delivery) at:
- 20 weeks of pregnancy or later or
- 500 g birth weight or higher
- the death of a fetus in the womb (before delivery) at:
- premature birth
- life-threatening illness in your baby or death shortly after birth