After weeks of dithering about the source of an E. coli outbreak that has killed 31 people, sickened more than 3,000 and triggered economic upheaval among produce suppliers across Europe, health officials confirmed yesterday that sprouts from an organic farm in Germany were to blame.

No tests of the sprouts from the farm in Lower Saxony came back positive but officials linked hospitalised patients to restaurants and then farm fields.

"It was possible to narrow down epidemiologically the cause of the outbreak of the illness to the consumption of sprouts," the president of the national disease control centre, said Reinhard Burger, said yesterday. "It is the sprouts."

The breakthrough came after an expert team 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-Schöneburg, of the consumer protection agency.

Mr Burger said all the tainted sprouts would probably have either been consumed or thrown away by now, but warned that the crisis was not over and that people should avoid sprouts. But authorities lifted the warning against eating cucumbers, tomatoes and lettuce.