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What is listeria?

Listeria is a bacterium primarily found in soil and water. Vegetables can become contaminated from soil or from manure used as fertiliser. Animals carrying the bacterium can also contaminate food. Listeria has been found in many types of uncooked foods, such as meats and vegetables, as well as in processed foods that become contaminated after processing, such as soft cheeses (such as feta and crumbled blue cheese), cooked sliced meats and pre-packaged sandwiches.

Unpasteurised milk or foods made from unpasteurised milk may also be sources of listeria infection. Listeria is killed by pasteurisation, and heating procedures used to prepare ready-to-eat processed meats should be sufficient to kill the bacterium. However, unless good manufacturing practices are followed, contamination can occur even after processing.

Public Health England says those at increased risk from listeriosis caused by listeria include:


Listeria symptoms

Symptoms of a listeria infection can include:

If listeria infection spreads to the nervous system ( brain and spinal cord), the following symptoms can occur:

  • Headache
  • Stiff neck
  • Confusion
  • Loss of balance
  • Convulsions

Infected pregnant women may experience only a mild, flu-like illness. However, infection during pregnancy can lead to premature delivery, infection of the newborn or even stillbirth. There is no routine screening test to find out if you are likely to contract listeriosis during pregnancy. If you have symptoms of listeriosis, seek medical advice immediately.

How is listeriosis diagnosed and treated?

Illness caused by listeriosis can develop after just a day or up to 90 days later. The average incubation time is about 30 days.

Around 5% of people may carry the disease but do not become ill from it.

Listeria infection is often diagnosed by medical history and confirmed by blood or spinal fluid tests.

Antibiotic treatment will usually cure the infection, and when given promptly to an infected pregnant woman, may prevent infection of her foetus.

Even with prompt treatment, some infections result in death. In the elderly and people with serious medical problems, these infections are more likely to be fatal.

WebMD Medical Reference

Medically Reviewed by Dr Rob Hicks on February 24, 2017

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