Listeria

This is a type of food poisoning which is caused by eating food that has been infected with the listeria bacteria. This is known as ‘listeriosis’.

Listeria poisoning affects a wide range of people but is especially problematic for pregnant women, newborn babies and people with a weakened or compromised immune system. This particularly applies to the over 60’s.

Listeria Monocytogenes

This is the name given to the bacteria which causes listeria food poisoning. These bacteria are rod shaped in appearance and is one of the most dangerous forms of pathogenic bacteria known to humans.

These bacteria are found in poultry, sheep, cattle, dairy foods, fruit and vegetables. They enter the body via the gastrointestinal tract and release toxins which damage cells within the body. It also spreads through the bloodstream where it particularly targets the nervous system.

However it is considered a rare form of food poisoning and one that is treatable. But, it is nevertheless, a serious type of food poisoning which is particularly dangerous for pregnant women, the elderly and anyone with poor immunity.

Foods which contain the listeria bacteria

These bacteria are usually found in soft cheeses such as Brie or Camembert but it also appears in the following foods:

• Pates
• Butter
• Ice cream
• Sliced meats
• Poultry, e.g. cooked chicken
• Smoked salmon (packaged)
• Packaged sandwiches
• Unpasteurised milk
• Canned fish
• Unwashed fruit and vegetables

Listeria is a tough, durable type of bacteria which can resist extremes of temperature much better than other bacteria. It even thrives at temperatures of minus 24 Fahrenheit which means that it is able to survive refrigeration.

Refrigeration usually kills off most strains of bacteria but listeria appears to have a stronger than normal survival instinct in this respect.

Causes of listeria food poisoning

Listeria is caused by consuming food which has been contaminated by the listeria monocytogenes bacteria. These bacteria invade cells within the lining of the intestinal walls and releases toxins which cause an infection.

These bacteria are able to travel throughout the body but are particularly attracted to the nervous system. This leads to a range of health problems such as meningitis and septicaemia.

These bacteria are found in a variety of foods which include processed ready meals, side salads such as coleslaw (mixed vegetables in mayonnaise), cooked poultry and canned fish.

But one of the biggest high risk foods is soft cheese. These include Brie, Camembert, Ricotta and Feta and have been highlighted as one of the main causes of listeria food poisoning.

Symptoms of listeria food poisoning

The time between the consumption of the contaminated food and the appearance of the first symptoms is known as the ‘incubation period’.

With listeria, the symptoms take much longer to appear than with most other types of bacteria. In fact, it can be 8 weeks before the symptoms develop.

But, symptoms usually appear after a month which appears to be the average.

The symptoms start off as relatively mild but soon worsen once the immune system has been infected. They include:

• Fever
• Nausea
• Vomiting
• Diarrhoea
• Muscle aches and pains
• Tiredness
• Loss of appetite

These are the initial symptoms of listeriosis and in many ways will feel like a bad case of ‘the flu’.

But if the infection has affected the immune system it will cause the following symptoms:

• Poor balance
• Lack of co-ordination
• Severe headaches
• Stiff neck
• Seizures
• Confusion

Meningitis or septicaemia is likely to develop if the infection has spread to the brain or throughout the bloodstream.

Listeria food poisoning and pregnancy

The group of people who are at a very high risk of listeriosis are pregnant women.

If a women contracts listeria food poisoning during her pregnancy then she will experience the symptoms mentioned above but these may be relatively mild.

However, the risks to the unborn baby are anything but mild.

These bacteria are able to transfer from the mother to the baby via the placenta or at birth. If this happens they will enter the baby’s bloodstream and once there, will cause a serious infection.

This will result in either a stillborn baby or a miscarriage.

Pregnant women appear to be a greater risk of listeria food poisoning than other women which means that they need to take greater care about what they eat and food safety in general.

This is covered in more detail in our pregnancy and food poisoning section.

Other high risk groups and listeria food poisoning

These include people who have undergone a transplant; cancer treatment, e.g. chemotherapy; who suffer from HIV or AIDS or have kidney or liver disease. This is because their immune systems are less effective at fighting off bacteria which cause infections such as listeriosis.

People in any of these groups are more likely to develop a serious form of this illness and/or complications.

Diagnosing listeria food poisoning

Contact your GP if you have developed symptoms of this illness within the last month or two. Do this if you are in a high risk group, for example, you suffer from diabetes.

A blood test can detect the symptoms of listeria food poisoning. Another equally useful test is a spinal fluid test.

If you are pregnant then your GP will perform a blood test to check for signs of this illness.

Treatment for listeria food poisoning

Listeriosis can be treated with antibiotics. If this food poisoning has occurred during pregnancy then antibiotics will be given to the mother as soon as possible to prevent the risk of the infection spreading to the unborn baby.

Antibiotics are also prescribed if a newborn baby exhibits these symptoms although it may be given a different type or combination compared to an adult.

Preventing listeria food poisoning

There are a few measures you can take to avoid the risk of you contracting this form of food poisoning. These are especially important if you are pregnant or have a poorly functioning immune system.

They include:

• Avoid eating canned meats and meat based products such as ham, luncheon meat and hot dog sausages.
• Avoid soft cheeses such as Brie unless you know that they have been produced from pasteurised milk.
• Avoid canned fish or pates.
• Wipe kitchen surfaces, utensils and containers after use.
• Store raw and cooked food separately

These will reduce the risk of listeriosis.