Family doctor

listeria

Overview:

• Listeria is a form of food poisoning which rarely affects healthy people
• Those at high risk include pregnant women, newborn infants, the elderly, and those with weak immune systems
• Foods at high risk from listeria contamination include certain deli foods, hot dogs, uncooked meat, ready-to-eat foods, mussels, soft cheese and unpasteurised milk
• Listeria has a long incubation period of between 11 to 70 days
• Healthy people can get a milder form of the illness which strikes just one day after eating contaminated food

What is it?

Listeria is a form of food poisoning which rarely affects healthy people. However, the disease can be fatal in unborn children, newborn babies, and those with weak immune systems.

Listeria is different from other food poisons because it grows at fridge temperature - rather than room temperature like other food borne illnesses.

Foods most likely to be contaminated with listeria include deli foods such as cold meats, pate, soft cheese, and unpasteurised milk, uncooked meats, hot dogs and ready-to-eat seafood such as mussels.

A large listeria outbreak in 1985 in America which lead to 48 deaths was linked to Mexican soft cheese. In the U.S. it is estimated more than 1000 people become seriously ill and 250 people die from listeriosis each year.

The illness generally has a long incubation period of up to two months when it is infects pregnant women and those with weak immune systems.

Another recently recognised Listeria syndrome called "febrile gastroenteritis" has been reported in healthy people, and this illness usually strikes within one day and only lasts up to three days. The main symptoms are fever, diarrhoea, headache and stomach ache. It is not a serious illness in healthy people.

High risk groups:

• Pregnant women and their fetuses
• Newborn babies can be born with listeria if their mothers' contracted it during pregnancy
• People with AIDS
• Those with immune deficiencies
• Patients having chemotherapy for cancer
• Diabetics
• People with kidney disease
• The elderly
• Those taking steroid medications

Pregnant women are at 20 times more risk of listeria than healthy people, and one third of cases of listeriosis occur in pregnancy women. People with AIDS are at 300 times more risk of serious illness from listeria than the general population.

What are the symptoms?

Listeria causes a flu-like illness with a fever, headache, and sometimes nausea and diarrhoea. The illness normally strikes within two to eight weeks after eating contaminated food, but it can take up to 10 weeks to become ill.

Pregnant women infected with listeria can experience fever and chills and should contact their doctor as soon as possible because drug treatment can prevent a spontaneous abortion or stillbirth.

In others, the illness begins with fever and muscle aches. Symptoms such as a stiff neck, loss of balance, and seizures can occur if the infection spreads to the nervous system.

Anyone who feels ill and suspects food poisoning with listeria in the past two months should contact their doctor, especially those with existing health problems.

People who do not get sick but may have eaten contaminated food products do not need to see a doctor, even if they are in a high risk group.

Listeria can be diagnosed with a blood test or spinal fluid test.

What can be done?

Antibiotics are given to pregnant women who have been infected with listeria. This can prevent the infection passing to the fetus.

Antibiotics are also given to other high-risk groups. However, the elderly and those with serious medical problems may not be cured, despite prompt medical attention.

Prevention measures for pregnant women and those with weak immune systems:

• Avoid eating deli foods such as cold cuts - or reheat them before eating them.
• Check use-by dates on all ready-to-eat foods and examine the food and packaging before you buy and before eating it.
• Avoid cold rice and uncooked seafood (sushi may contain listeria).
• Avoid pate because this can carry listeria.
• Cook hot dogs and other pre-prepared meats until they are piping hot.
• Avoid soft cheeses such as camembert, brie, and blue vein. (Processed cheese such as cheddar, cream cheese, cottage cheese and yoghurt are safe to eat).
• Avoid ready-to-eat seafood such as mussels and oysters, or cook them before eating them.
• Practise safe food hygiene and avoid cross contamination of vegetables with raw meat by storing them separately. (See FamilyDoctor article on food safety).
• Wash cutlery and chopping boards after handling raw meat or deli food.

Prevention measures for the general population:

• Check food and packaging before buying and before eating it. Be careful when buying deli foods, ready to eat meats, seafood, soft cheese and hot dogs - always observe the use-by dates.
• Cooking food until it is piping hot will kill any listeria infection.
• Practise safe food handling and store vegetables and raw meat separately. (See FamilyDoctor article on food safety).
• Wash chopping boards and utensils after handling raw meat.

Getting help

Pregnant women and other at-risk groups should see their doctor promptly about any flu-like illness. It is advisable for pregnant woman to be aware of foods associated with an increased listeria risk.