Two of the patients died at Manchester Royal Infirmary. The third death happened at Aintree University Hospital NHS Foundation Trust.
In total, six hospital patients who were seriously ill in hospital contracted listeria.
Why is listeria dangerous?
The bacteria in listeria can cause listeriosis. It is usually caught from eating food containing listeria bacteria. Listeria infection in healthy people is usually either unnoticed or may cause very mild illness.
However, it can have more serious consequences for some people, particularly those with pre-existing health conditions and pregnant women.
Mild symptoms of listeriosis include a high temperature of 38C or above, aches and pains, chills, feeling sick or vomiting, diarrhoea.
The time between exposure to the organism and the development of the illness can be up to 70 days.
Occasionally, however, a more serious infection develops and spreads to the bloodstream or brain.
Good food hygiene is paramount to prevent listeriosis.
Which foods pose a greater risk of listeriosis?
It is mainly a problem with:
dairy products made from unpasteurised milk
soft cheeses, like camembert and brie
chilled ready-to-eat foods, like prepacked sandwiches, pâté and deli meats
How do you avoid listeriosis?
Wash your hands regularly with soap and water
Wash fruit and vegetables before eating them
Store ready-to-eat foods as recommended by the manufacturer
Make sure all hot food is steaming hot all the way through
Do not eat food after its use-by date, even if it looks and smells normal
What are the symptoms of listeriosis?
High temperature of 38C or above
Aches and pains
Feeling sick or vomiting
More serious problems can occur if you're pregnant or have a weak immune system and can lead to an infection spreading to the blood stream or brain.
If you're pregnant, you should avoid eating the following foods that have the highest risk of causing listeriosis:
Some uncooked soft cheeses – including brie and camembert
All types of pâté – including vegetable pâté
Unpasteurised milk or dairy products
Any undercooked food
Call 999 or go to A&E if you have the following symptoms:
a severe headache and stiff neck
discomfort when looking at bright lights
a rash that does not fade when a glass is rolled over it – the rash may be blotchy, like bruises or small red pinpricks
These could be symptoms of meningitis caused by listeriosis, which needs to be treated in hospital straight away.