Listeriosis - Protecting yourself and eating safely

Listeriosis is a rare but potentially serious infection caused by the bacterium Listeria monocytogenes. On average each year, there are between 14 and 22 cases of listeriosis reported in Ireland. Listeriosis is a notifiable disease in Ireland.

How you get listeriosis

People become infected by eating food that is contaminated with listeria. The incubation period (the time between the listeria getting into the body and symptoms first appearing) ranges between 3 and 70 days. The average incubation period is 3 weeks. If a woman eats contaminated food during pregnancy, the infection can be passed across the placenta to the baby.

Symptoms of listeriosis

In healthy people, listeria infection (listeriosis) generally causes either no symptoms or only mild, self-limiting flu-like symptoms with, very occasionally, gastroenteritis. Mild infections like this only affect the lining of the gut.

In more vulnerable people who are at greater risk, the disease can become invasive and get into the bloodstream.

In older and immunocompromised people (with weak immune system/body defences), the infection can occasionally spread to the central nervous system causing meningitis and/or bloodstream infection, with symptoms such as headache, stiff neck, confusion, and loss of balance or convulsions.
Pregnant women who are infected may have no symptoms or experience only a mild flu-like illness. However, infection during pregnancy can lead to her baby becoming infected and result in miscarriage, stillbirth, premature labour or meningitis in the newborn baby. For further information for pregnant women go to Listeria advice for pregnant women

Who is at most risk for listeriosis?

Anyone can become ill from eating food contaminated with listeria, although the disease primarily affects the following vulnerable groups of people:

Older people
Immunosuppressed people (e.g. persons with HIV/AIDS, cancer, diabetes)
Pregnant women (and their unborn children)
Newborns and young children

How is listeriosis diagnosed?

Diagnosis is usually made by testing the patient’s blood or cerebrospinal fluid (the fluid bathing the brain and spinal cord). During pregnancy, a blood test is the most reliable way to find out if symptoms are due to listeriosis.

How does Listeria get into food?

Listeria monocytogenes is widespread in the environment and can be found in soil and water. Vegetables can become contaminated from the soil or from manure used as fertilizer. Animals can carry the bacterium without appearing ill, and meat or dairy products from these animals can be contaminated. Foods may also be contaminated after processing, e.g. cheese.

How is listeriosis treated?

Listeriosis can be treated with antibiotics. However, even with treatment, infection can be severe and may result in death, especially in older people.

How can I protect myself from listeriosis?

Protecting yourself against listeriosis is particularly important for pregnant women, infants, older people and those with weakened immune systems. As with other foodborne illnesses, there are several measures that will help to reduce your risk of infection with listeria:

Always wash your hands before and after preparing food, and before eating.
Cook food thoroughly, especially meat and meat products, chicken and vegetables, and pre-prepared, ready to heat meals, ensuring that they are cooked through to the middle and piping hot (food that requires cooking should reach 75°C for at least 30 seconds).
Wash salads, fruit and raw vegetables thoroughly before eating, or peel if appropriate.
Keep uncooked meats separate from vegetables and from cooked and ready-to-eat foods
Wash hands, knives, and cutting boards after contact with uncooked food
Make sure that your refrigerator is working correctly (it should be kept between 0°C and 5°C)
When heating food in a microwave, ensure you follow heating and standing times recommended by the manufacturer
Keep foods for as short a time as possible and follow storage instructions including 'use by' dates
Throw away left-over reheated food. Cooked food which is not eaten immediately should be cooled as rapidly as possible and then stored in the refrigerator

What foods should I avoid if I am vulnerable to listeria infection?

The foods of most concern are those that do not require any further cooking or reheating such as chilled ready-to-eat foods. Foods most often associated with infection are ready-to-eat refrigerated and processed foods such as pre-prepared cooked and chilled meals, soft cheeses, cold cuts of meat, pâtés and smoked fish. Increasingly, outbreaks of listeriosis associated with fresh produce (particularly fresh vegetables that undergo little or no heat treatment) are being reported.

The following foods have been associated with an increased risk of listeriosis:

Any drinks or food made with raw (unpasteurised milk). This includes:
- Raw unpasteurised milk and any drinks that use raw milk (such as smoothies)
- Soft cheeses with white rind (e.g. Brie, Camembert, goat’s cheese)
- Blue-veined cheeses (e.g. Stilton, Roquefort, Gorgonzola)
Ready-to-eat cooked meats or meat products
Cured or fermented meats or meat products eaten without further cooking e.g. Parma ham, salami, chorizo, pepperoni
Ready-to-heat meals
Raw or smoked ready-to-eat fish, e.g. smoked salmon, smoked mackerel, marinated salmon, sushi, sashimi
Ready-to-eat cooked crustacean meat e.g. crabmeat, lobster, prawn
Live or cooked bivalve molluscs e.g. oysters, mussels, scallops, clams
Ready prepared pre-packed chopped salads e.g. leaves, sprouted seeds, coleslaw
Prepared salad items loose from salad bars/deli e.g. coleslaw, potato salad
Pre-packed sandwiches
Custom-made sandwiches from sandwich bars/deli
Any paté (including vegetarian)
Precut/prepared fruit, e.g. melon, fruit salad
Frozen vegetables eaten without further cooking

What should I do if I think I have Listeria?

For the great majority of healthy adults and older children, listeria is not a significant problem. If infected, symptoms will be short lived and self-limiting. However, if you are in one of the vulnerable groups and have concerns about symptoms or suspect you've eaten contaminated food, you should contact your GP or healthcare provider.

Last updated: 25 July 2025