BERLIN — A day after German agricultural officials identified locally grown sprouts as a possible cause of the E.coli outbreak that has killed 22 people and sickened more than 2,200, the officials said Monday that initial tests had failed to show conclusively that the bacteria originated with the sprouts.

Results from the first 23 of 40 tests on several varieties of sprouts came back negative, said officials from the agriculture ministry in the state of Lower Saxony. The ministry did not indicate when the remainder of the test results would be known.

“Based on previous experience during the examination of part of the sample,” the ministry said in a statement, “we assume that intensive analytical effort will be necessary to identify the pathogen with certainty.”

The confusing signals mark the second time that German officials publicly identified a probable cause of the outbreak, only to pull back later. They had said earlier that cucumbers from Spain were suspected as the cause, and then said tests had ruled out that hypothesis.