Salmonella is present in one in every 30 boxes of eggs imported for sale in England, a food watchdog study says.
Vulnerable people are warned to cook eggs thoroughly
With eggs from Spain, this rises to one in eight, according to the Food Standards Agency (FSA).
The FSA estimated the levels after tests on 1,744 imported boxes on sale in London and the North West, in small shops and discount chains.
It said the vast majority of eggs were free of salmonella, but urged the vulnerable to cook eggs thoroughly.
In their tests on the 1,744 boxes, researchers found salmonella inside eggs in 10 boxes, and contaminated egg shells in 157 boxes.
They then used their findings with other data on imported eggs to give a broader, more accurate picture, and estimated salmonella was present in 3.3% of boxes.
The samples came from eight European countries, with two-thirds coming from Spain.
Most of the contaminated eggs came from three farms in Spain, the FSA said.
France had the second highest number, with one in every 170 boxes found to be contaminated.
Dr Andrew Wadge, director of food safety for the FSA, said: "The vast majority of eggs we eat in the UK are salmonella-free.
"However this survey shows that problems with salmonella in eggs have not gone away."
He said the European Commission had set targets for reducing salmonella in laying flocks and making vaccination compulsory in countries with high contamination.
Only 10% of eggs sold in the UK were imported, and most imported eggs were used in the catering trade, said the FSA.
But the watchdog advised the elderly, the young, pregnant women and the sick to cook eggs thoroughly to reduce any risk of food poisoning.
Salmonella is a type of bacteria and poisoning usually occurs from eating contaminated food such as meat and eggs.
Infection causes severe diarrhoea, cramping abdominal pain, nausea and sometimes vomiting.
The symptoms can last for several days, but most people make a full recovery within a week.
In June, confectionary giant Cadbury Schweppes withdrew one million chocolate bars after a pipe at its plant in Marlbrook, Herefordshire, caused salmonella contamination.