Tests done on a food factory in Hungry found it was the source of an outbreak of listeriosis.
Contaminated products are being sold in shops in Britain and Northern Ireland, putting unwitting consumers at risk.
Two people have died and close to a dozen have fallen ill since 2015.
The European Food Safety Authority also warned about eating uncooked frozen products including spinach and green beans. Both cases of listeriosis in the UK last year resulted in death.
Dr Kathie Grant from Public Health England said: “Most people won’t have any symptoms of the infection or will only experience mild symptoms such as vomiting and diarrhoea, which usually pass within a few days without the need for treatment.”
But she warned: “More serious infection can develop in those with weakened immune systems or in vulnerable groups including babies, the elderly or pregnant women.
“The best way to prevent listeriosis is to practise good food hygiene.
“Along with the FSA, FSS (Food Standards Scotland) and HPS (Health Protection Scotland), we are reminding people that most frozen vegetables, including sweetcorn, need to be cooked before eating.
“This includes if adding them to salads, smoothies or dips.”
The EFSA warned the extent of the outbreak had initially been underestimated. Recent cases showed the outbreak was still ongoing.
Their report added: “It is strongly recommended that the processing plant concerned is completely cleaned and disinfected, which involves dismantling and thoroughly cleaning and disinfecting all the plant equipment, as well as any additional surfaces that may represent a point of contamination.”
Listeriosis is a rare infection caused by bacteria called listeria.
It usually goes away on its own, but can cause serious problems if you’re pregnant or have a weak immune system.
Listeriosis is usually caught from eating food containing listeria bacteria.
You can get it from lots of types of food, but it is mainly found in
- unpasteurised milk
dairy products made from unpasteurised milk
soft cheeses, like camembert and brie
chilled ready-to-eat foods, like prepacked sandwiches, pâté and deli meats