Cucumbers, tomatoes and lettuce were given an official all-clear Friday by German authorities, who said the evidence was strong that sprouts grown from beans or peas caused an E coli outbreak that has killed 30 people.

"It's the sprouts," said Reinhard Burger, head of the Robert Koch Institute, the federal infectious-disease laboratory.

He said the finding was based on a study of coach passengers who ate in a restaurant: every passenger who chose a dish with sprouts on it had fallen sick with bloody diarrhoea, the first sign of an enterohaemorrhagic Escherichia coli (EHEC) infection.

The market garden, the Bienenbuettel Gaertnerhof, has been closed.

The warning against the other three vegetables was issued May 25 and caused a massive slump in Europe's produce trade.

The new strain of E coli which causes kidney and nerve damage has been on the loose in Northern Germany since the start of May. Though found in faecal samples of patients, it has not been traced on any fresh food.

The rate of infections has begun to decline, Mr. Burger said.