BERLIN - In a surprising U-turn, German officials said initial tests published Monday provided no evidence that sprouts from an organic farm in northern Germany were the cause of the country's deadly E. coli outbreak.

The Lower-Saxony state agriculture ministry said 23 of 40 samples from the sprout farm suspected of being behind the outbreak have tested negative for the highly agressive, "super-toxic" strain of E. coli bacteria. It said tests were still under way on the other 17 sprout samples.

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"The search for the outbreak's cause is very difficult as several weeks have passed since its suspected start," the ministry said in a statement, cautioning that further testing of the sprouts and their seeds was necessary to achieve full certainty.

Negative test results on sprout batches now, however, do not mean that previous sprout batches weren't contaminated.

The ministry statement about samples from the Gaertnerhof organic sprouts farm in the northern German village of Bienenbuettel left consumers across the continent still puzzled as to what is safe to eat. The ministry itself also said it was not clear how soon an answer woud be found.

"A conclusion of the investigations and a clarification of the contamination's origin is not expected in the short term," the ministry added.

The current crisis is the deadliest E. coli outbreak in modern history, killing at least least 22 people and sickening more than 2,300 across Europe.