Consumers are being warned to boil any imported frozen berries for at least 60 seconds before eating them, in response to fears over a food-poisoning outbreak of the hepatitis A virus.

According to the Food Safety Authority of Ireland (FSAI), a few Irish cases of hepatitis A have been reported ‘which cannot be explained by travel abroad'.

"Investigations are underway to establish if there may be a link with contaminated imported frozen berries or other foods," it said.

Hepatitis can be mild, lasting less than two weeks, or more severe, lasting a number of months. Symptoms include loss of appetite, fever, nausea, abdominal pain and fatigue. These are followed a few days later by jaundice. Symptoms tend to be more severe the older a person is.

The virus is spread through the faeces of infected people, but can also be spread through contaminated water or through food that has been contaminated by infected food handlers.

This advice about boiling berries before consumption was originally given last year after a food-poisoning outbreak of hepatitis A, that was linked to frozen imported berries, was identified in Ireland, but was later found to have affected a number of European countries.

The advice is now being renewed as a result of the unexplained hepatitis A cases and the publication of a report into the European outbreak last year, which has concluded that some contaminated frozen berries may still be circulating in the food chain.

The original hepatitis A outbreak was first identified in Germany in May 2013. To date, over 1,400 cases have been reported in 12 European countries, with Italy the worst affected. Twenty-five cases were reported in Ireland, 21 of which were confirmed.

However, no single point source of contamination was ever identified, although 12 food operators were identified with links to contaminated batches.

"As contaminated imported frozen berries could still be circulating in the food chain, we continue to recommend the boiling of imported frozen berries for at least one minute before eating them. This is a precautionary measure and will destroy the virus if it is present.

"There is no evidence that fresh Irish berries were the cause of the outbreak. However, we suggest that - as with all other fruit and vegetables - fresh berries should be washed thoroughly if they are being eaten uncooked," commented FSAI chief executive, Prof Alan Reilly.

He added that this outbreak shows ‘how complex the food chain can be'.