“We are now looking towards cucumbers as the most probable source of the illnesses,” said Cornelia Pruefer-Storcks, health senator in the northern German city of Hamburg.

A fourth cucumber has also tested positively for enterohaemorrhagic E. coli (EHEC), although authorities were not certain where the salad vegetable came from.

The Robert Koch Institute, the national disease centre, says that more than 200 people have been diagnosed as suffering from haemolytic uraemic syndrome (HUS), caused by EHEC, and that at least two people have died.

There are hundreds of other suspected cases, all of which have come to light in the past two weeks. Officials say the high number is very unusual as there are normally just 1,000 EHEC infections and 60 cases of HUS per year.

Children normally have a higher risk of contracting HUS, but in the latest outbreak adults, mostly women, have been felled by the disease which can result in acute renal failure, seizures, strokes and coma.

Consumer Affairs Minister Ilse Aigner said this week she was “really worried” by the outbreak and her ministry has warned people to especially careful when eating tomatoes, lettuce, and cucumbers.