Officials determined on Friday that sprouts grown at the farm in Lower Saxony state, in northern Germany, were the culprit in the outbreak - which has struck more than 3,000 people.
But the state's agriculture ministry said yesterday that it still isn't clear whether workers brought in the bug, or whether the bacteria got into the farm on seeds or by some other means. Tests on 1,100 samples, 300 of which are from the farm, are ongoing.