Listeriosis is a rare infection typically caused by eating food contaminated with listeria bacteria. Foods that can be particularly risky include cold and cured meats, smoked and cured fish, shellfish and mouldy cheeses such as camembert and brie. Previous outbreaks have also been linked to pre-prepared sandwiches.

The UK Health Security Agency has confirmed it is investigating five linked cases of listeria infection in people who fell sick between May and December. Three died with at least one death attributed to listeria and two others known to have been infected when they died. The cases are thought to be linked to desserts supplied to NHS hospitals and care homes.

What are the symptoms of listeriosis?

Most people infected with the bacteria suffer no symptoms or only mild signs such as a high temperature, vomiting, aches and pains, chills or diarrhoea, according to the NHS website.

Pregnant women may also experience stomach ache or notice their baby moving less than usual. Babies who are affected may be irritable and feed less than usual.

Parents are advised to call 999 or go to A&E if children suffer more severe symptoms including a severe headache and stiff neck, discomfort looking at bright lights, seizures, sudden confusion or sleepiness, and a rash that does not fade when a glass is rolled over it.

How dangerous is listeriosis?

Cases are usually mild but some people are at higher risk, including pregnant women, newborn babies and patients with weakened immune systems. Risk also increases with age.

It can usually be managed at home with rest and plenty of fluids. Some people may be prescribed antibiotics to help them clear the infection more quickly.

How can you reduce your risk of contracting listeriosis?

Make sure your fridge is working properly, with a temperature below 5C, and keep chilled, ready-to-eat foods cold. Once removed from the fridge, consume such foods within four hours.

Ensure you eat, cook or freeze foods by their use-by date and follow the  storage instructions, while keeping raw and ready-to-eat foods separate. Ensure any food is properly cooked through and wash your hands regularly before and during food preparation.

Pregnant women and people with compromised immune systems are advised to avoid ready-to-eat cold-smoked or cured fish products such as smoked salmon.

Mums-to-be should also avoid some soft cheeses unless cooked, pâté, unpasteurised milk or dairy products and undercooked food.