Causes of listeriosis (Listeria)

Learn about the cause of listeriosis, how it is spread and where it is found.

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What causes listeriosis?

Listeriosis is caused by infection with Listeria bacteria.

How is listeriosis spread?

Listeriosis can be spread:

  • during pregnancy from mother to baby
  • when you eat food or drink water that has been contaminated with Listeria

You can spread Listeria between foods if you do not follow proper food handling practices.

Listeria can also be spread from contact with infected animals. Farmers and veterinarians can get the illness from contact with domestic farm animals. This can happen when they help animals give birth or when farmers butcher an animal for meat.

Generally, listeriosis is not spread between people.

Where is it found?

Listeria is found in soil, sewage and untreated water everywhere. It can also be found in the following foods:

  • fish
  • meat
  • seafood
  • fruits and vegetables
  • dairy products, such as milk and cheese

However, some foods are more likely to be contaminated than others.

How does food and water become contaminated?

Listeria bacteria live in the environment and can naturally exist in:

  • soil
  • plants
  • untreated water

Listeria can also get into sources of water when feces from infected animals enter the water supply.

Fruits and vegetables can get contaminated if contaminated water is used on crops. They can also become contaminated from Listeria in soil and manure-based fertilizers.

Listeria bacteria can contaminate facilities where food is processed and manufactured. This can happen when:

  • contaminated water is used for cleaning or rinsing
  • the ingredients coming into the facility are contaminated

Once Listeria enters a facility, it can sometimes contaminate the foods that are manufactured there. 

Meat and dairy products can be contaminated even if the farm animals appeared healthy when processed.

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