FILE - In this June 5, 2011 file picture greenhouses at an organic farm that grows bean sprouts are photographed in the Uelzen district, northern Germany, Sunday, June 5, 2011. Investigators have determined that German-grown vegetable sprouts are the cause of the E. coli outbreak that has killed 29 people and sickened nearly 3,000, the head of Germany's national disease control center said Friday, June 10, 2011. Reinhard Burger, president of the Robert Koch Institute, said even though no tests of the sprouts from an organic farm in Lower Saxony had come back positive for the E. coli strain behind the outbreak, an investigation into the pattern of the outbreak had produced enough evidence to draw the conclusion. (AP Photo/dapd, Axel Heimken,File)
BERLIN (AP) — German authorities say they haven't yet been able to resolve how sprouts at a farm became contaminated with an aggressive strain of E. coli that has been blamed for 33 deaths.
Officials determined Friday that sprouts grown at the farm in Lower Saxony state, in northern Germany, were the culprit in the outbreak — which has sickened more than 3,000 people.
But the state's agriculture ministry said Sunday that it still isn't clear whether workers brought in the bug, or whether the bacteria got onto the farm on seeds or by some other means.
The ministry says tests on some 1,100 samples, nearly 300 of them from the farm, are ongoing in an effort to answer that question. But it says that they have produced no positive results yet.