Listeriosis is an infection that is usually contracted by eating food that has been contaminated by a type of bacteria called listeria monocytogenes. Listeria monocytogenes is commonly known as listeria.
The listeria bacteria has been found in a range of chilled ‘ready-to-eat’ food, such as:
- pre-packed sandwiches,
- pâté,
- butter,
- soft cheeses such as Brie or Camembert or others with a similar rind,
- soft blue cheese,
- cooked sliced meats and
- smoked salmon.
Types of listeriosis
There are two types of listeriosis:
- non-invasive listeriosis - where the infection remains limited to the digestive system, and
- invasive listeriosis - where the infection spreads into the blood (sepsis) and/or the central nervous system, before spreading to the brain; both these types of secondary infection can be potentially fatal.
Non-invasive listeriosis
Most cases of listeriosis are non-invasive, and people with non-invasive listeriosis will experience mild flu like symptoms, such as fever and muscle pain, as well as episodes of diarrhoea.
Invasive listeriosis
People with weakened immune systems are particularly vulnerable to invasive listeriosis.
Those with weakened immune systems include:
- older people who are over 60 years of age,
- pregnant women and their unborn babies,
- babies who are less than one month old,
- people with a health condition that weakens the immunes system, such as HIV, AIDS, or diabetes, and
- people who are having medical treatments that weaken their immune system, such as chemotherapy, or radiotherapy.
Invasive listeriosis is a very serious medical condition, and requires immediate admission to hospital so that the infection can be aggressively treated with antibiotics.
Listeriosis and pregnancy
Pregnant women are also vulnerable to getting listeriosis. This is because the hormonal changes that occur during pregnancy weaken the body’s natural defences against the listeria bacteria.
Pregnant women are 20 times more likely to contract listeriosis compared with the rest of the population.
Listeriosis that is contracted during pregnancy does not usually pose a serious threat to the mother’s health. However, it can be very damaging to her unborn child, and can result in miscarriage, still-birth, or the death of the baby shortly after birth.
How common is listeriosis?
It is hard to estimate how common non-invasive listeriosis is because many people mistake the condition for the flu, or a ‘stomach bug’, and do not report their symptoms to their GP.
Health regulations regarding food production and storage were tightened up following a number of cases of listeriosis that occurred during the 1980s which were linked to contaminated food.
Outlook
The outlook for non-invasive listeriosis is good. Symptoms tend to be short-lived and usually pass within three days without the need for treatment.
The outlook for invasive listeriosis is poor. An estimated 35% of people with invasive listeriosis will die due to complications that arise from the infection.
Contracting a listeriosis infection during pregnancy carries a moderately high risk of experiencing significant complications. It is estimated that 22% of pregnancy-related cases of listeriosis will result in the death of the baby.
The best way to prevent listeriosis is to ensure you always practice good food hygiene, such as not using food past its ‘use by’ date, following storage instructions on food labels, making sure your fridge is between 0oC and 5oC and thoroughly cooking food.
If you are in a high risk group for listeriosis - for example, if you are pregnant, or have a weakened immune system, you should avoid eating foods, such as soft mould-ripened cheese, or pate. See the ‘prevention’ section for more information.