They've been blamed before, but this time, Germany's investigators feel quite certain that contaminated vegetable sprouts from a local farm caused Europe's current E. coli outbreak, the deadliest ever recorded.

"It is the sprouts," asserted Reinhard Burger, the head of the Robert Koch Institute, which is Germany's national disease control centre.

Burger said the outbreak, which has killed 29 and sickened nearly 3,000 -- including at least one Canadian -- is believed to have started on a small organic vegetable farm in Lower Saxony that first came under suspicion last weekend.

The farm was initially blamed for the outbreak on Sunday, but authorities backpedalled the following day, after lab tests for the particular E. coli strain behind the outbreak came back negative.

Tests of the sprouts are still negative, but investigators have closely studied the outbreak pattern and say there is enough evidence to conclude that the sprouts were to blame, Burger explained.

"People who ate sprouts were found to be nine times more likely to have bloody diarrhea or other signs of EHEC (enterohaemorrhagic E. coli) infection than those who did not," he said Friday at a joint press conference with heads of Germany's Federal Institute for Risk Assessment and Federal Office for Consumer Protection.

"In this way, it was possible to narrow down epidemiologically the cause of the outbreak of the illness to the consumption of sprouts."

The breakthrough came after a task force linked separate clusters of patients who had fallen sick to 26 restaurants and cafeterias that had received produce from the organic farm.

"It was like a crime thriller where you have to find the bad guy," said Helmut Tschiersky-Schoeneburg from the consumer protection agency.

As for how the sprouts got contaminated, that remains a mystery. Authorities do know that a rare strain of the E. coli, called O104:H4, which had never been seen in an outbreak before, caused the infections.

For now, investigators are simply pleased they've found the source.

"It is very satisfying to present this discovery today, to be able to isolate the cause and source of the infection," Burger said. "It is the result of intensive co-operation between German health and food authorities."

Sprouts are popular in Germany, where they are served in most salad bars and often in sandwiches.

With the decision, the warning against eating cucumbers, tomatoes and lettuce has been lifted, said Andreas Hensel, head of the Risk Assessment agency. That advisory, issued over two weeks ago, has cost vegetable farmers in Europe hundreds of millions of euros in lost sales.

While it is possible that all the contaminated sprouts have now either been consumed or thrown away, Hensel warned that the crisis is not yet over.

"There will be new cases coming up," he said.

E. coli infections typically incubate in the body for three to four days before symptoms begin to appear.

Some of the nearly 3,000 people who have become ill so far may yet develop hemolytic uremic syndrome (HUS), a serious complication that destroys red blood cells and can cause the kidneys to shut down.

Already, 722 of the 2,808 who have been sickened in Germany have suffered from HUS.

The World Health Organization says 97 others have fallen sick in 12 other European countries, as well as three in the United States. One Canadian who recently travelled to Germany also tested positive for the E. coli strain fingered in this outbreak.

"The number of new infections is declining," Burger told the news conference Friday.

With files from the Associated Press