Another scare has emerged in the egg industry in Europe, with more than four million eggs recalled in Poland because of antibiotics.
Poland's veterinary service recalled 4.3 million eggs after it was discovered that they contained higher than accepted levels of antibiotics.
Polish authorities said that laying hens had been given the wrong feed, resulting in high antibiotic levels.
The new scare came as it was confirmed that fipronil contamination had again been found on a number of layer farms in the Netherlands.
Fipronil - a banned chemical that was found to have been used as a red mite treatment on layers, and which caused the destruction of millions of hens last year - has again been found on a small number of the country's farms.
Dutch eggs have been withdrawn from sale in Germany as a result of new contamination.
The European Food Safety Authority (EFSA) recently produced a report on the original fipronil scandal last year.
EFSA found contaminated eggs or chicken in eight different European Union countries. One of the affected countries was Poland.
Now Polish authorities are dealing with a separate contamination crisis in the egg industry - this time involving antibiotics.
Poland's veterinary service said in a statement: "The recall is caused by the presence of residues of the antibiotic lasalocid at a rate exceeding its maximum allowed value." Lasalocid is an antibiotic used in treating coccidiosis.
The head of the Polish veterinary service, Pawel Niemczuk, said the drug was added "erroneously" to the feed given to laying hens on a farm near Poznan.
"The feed for fattening chickens (which legally uses the antibiotic) was mistakenly given to laying hens," he told the Polish news agency, PAP.
Polish authorities said the contaminated eggs had made it onto the shelves of the biggest grocery stores in Poland, including the Portuguese-owned Biedronka chain, French-owned Carrefour and the local Piotr i Pawel delicatessen chain.
They said it was possible that they were also being sold in other retail outlets.
Consumers have been warned that eggs that have already been purchased should not be consumed, but returned to the shops where they were bought.
Last year health authorities confirmed that eggs from Poland were linked to a resurgence of salmonella cases in this country.
Towards the end of 2016, there were more than 160 cases in the UK had been linked to a Polish packing centre.
The number of cases declined after Polish authorities took action, but Public Health England (PHE) subsequently confirmed that the numbers had increased again.
Another 73 cases were reported in the UK. The European Union said that more than 500 confirmed or probable cases in 14 countries had been linked to Polish egg production over the last year.
Last year a spokeswoman for PHE said: “In 2016, Public Health England and the Food Standards Agency (FSA) worked with European partners in investigating a multi-country outbreak of salmonella enteritidis linked to an egg packing centre in Poland.
“The outcome of the 2016 investigations resulted in the Polish authorities taking public health action on the implicated premises in Poland, including marketing restriction on the eggs produced at these premises.
“However, some new cases of salmonellosis caused by this specific outbreak strain have been identified in England.
The spokeswoman added: “PHE have notified ECDC (the European Centre for Disease Prevention and Control) and European colleagues of this finding and, in collaboration with the FSA, are carrying out further investigations into the source of infection of the new cases.”
The PHE said that, since the re-emergence of the outbreak, a total of 73 cases had been reported in the UK. The spokeswoman said that UK authorities were working with their counterparts in Europe to tackle the problem.
A report produced by the ECDC showed that the original outbreak was linked to eggs originating from three Polish packing centres.
The report said that the number of reported cases fell sharply after control measures were put in place in Poland in November 2016 but from March 2017 the number of newly reported cases increased again.
Egg industry leaders in the UK have been urging food companies to source their eggs from British producers to ensure that consumers are safe.
Testing found no trace of fipronil on UK farms, salmonella levels are very low in the UK and British egg production is not affected by the latest antibiotic contamination.