There has been a significant rise in the number of people in Europe infected by a strain of E. coli which has led to the deaths of 17 people, officials say.
More than 1,500 people in nine nations - though nearly all in Germany - have now been infected by enterohaemorrhagic E.coli (EHEC), which can cause the deadly haemolytic-uraemic syndrome (HUS).
The death toll in Germany has risen to 16, with officials saying an 84-year-old woman with HUS had died on Sunday.
The outbreak's source is not yet known.
Earlier, the Spanish government said it was considering legal action against the authorities in Hamburg for wrongly blaming its produce.
"We do not rule out taking action against the authorities who called into question the quality of our products," Deputy Prime Minister Alfredo Perez Rubalcaba told radio Cadena Ser.
Spain's fruit and vegetable exporters estimate they have been losing more than 200m euros ($290m; £174m) since the outbreak emerged.
Germany has admitted the bacteria did not come from Spain as initially reported, but said the decision to issue the warning had been correct as a different strain of E.coli was present in Spanish cucumbers.
"Hundreds of tests have been done and the responsible agencies... have determined that most of the patients who have been sickened ate cucumbers, tomatoes and leaf lettuce and primarily in northern Germany," German Agriculture Minister Ilse Aigner said.
"The states that have conducted the tests must now follow back the delivery path to see how the cucumbers or tomatoes or lettuce got here."
The Robert Koch Institute, the German federal institution responsible for disease control, said on Wednesday afternoon that 1,534 people in the country had been infected by EHEC.
EHEC is a deadly strain of E. coli bacteria, which is found in the digestive systems of cows, humans and other mammals.
On Tuesday, the RKI reported 1169 cases of EHEC, and said 470 people were suffering from HUS, up from 373 on Monday.
Experts said the number was unprecedented in modern medical history because HUS normally occurred in 10% of EHEC infections. They warned that the strain could be more dangerous than anything previously seen.
"There may well be a great number of asymptomatic cases out there that we're missing," Paul Hunter, a professor of health protection at the University of East Anglia, told the Associated Press.
"This could be a much bigger outbreak than we realise right now."
"There might also be something genetically different about this particular strain of E. coli that makes it more virulent."
But the European Commissioner for Health and Consumer Policy, John Dalli, ruled out any need for a ban on cucumbers, or for a warning against travelling to northern Germany.
"The outbreak is limited geographically to an area surrounding the city of Hamburg," he told reporters.
"It appears the outbreak is on the decline."
About half of the haemolytic-uraemic syndrome, HUS patients in Hamburg clinics have suffered neural disorders three to five days after falling ill, such as epileptic fits and slurred speech, according to the German newspaper, Die Welt.
Germany typically sees a maximum of 50 to 60 annual cases of HUS, which has a fatality rate of up to 5%, according to the World Health Organization (WHO).
Unusually, more than 60% of the EHEC cases in Germany have been women - 88% over the age of 20 - and nearly 90% of the HUS cases have been women over the age of 20, officials have said.
Experts have said this may be because women were the ones most likely to be eating fresh produce or handling food in the kitchen.
Hundreds of tests have been carried out by laboratories across Germany In addition to Germany, cases of EHEC have also been reported in eight other European countries - Austria, Denmark, the Netherlands, Norway, Spain, Sweden, Switzerland and the UK, the WHO said. All but two of those infected either live in Germany or recently travelled to Germany.
Fifteen cases of HUS and one related death have also been reported in Sweden, seven cases in Denmark, three in the Netherlands, two in the UK, and one in Spain, according to the European Center for Disease Prevention and Control.
Several countries have taken steps to curtail the outbreak, such as banning cucumber imports and removing the vegetables from sale.
Health authorities have also advised people to wash fruit and vegetables thoroughly, to do the same with all cutlery and plates, and to wash their hands before meals.