German scientists found no traces of E. coli O104:H4 bacteria at an organic vegetable farm believed to be the source of an outbreak that has killed 22 people, sickened 2,153 in Germany and 90 others in 10 European countires and the United States.  627 people have developed Hemolytic Uremic Syndrome.

Even though first lab tests on bean sprouts from the farm were negative, officials said they were not surprised because any contaminated produce could have been long since distributed.

“This is an important lead that we’re vigorously pursuing,” federal Agriculture Minister Ilse Aigner said in Berlin on Monday after the state agriculture ministry in Lower Saxony state said the 23 samples tested so far had been negative.

However, Aigner repeated warnings to consumers to avoid bean sprouts, cucumbers, tomatoes and salad and for good reason.  In its latest report, Germany’s Robert Koch Institute (RKI) said the source of the outbreak has not been identified, but fresh tomatoes, cucumbers and lettuce from the northern part of the country “must be considered to have the highest relative risk for infection compared to other foods investigated,” and these raw vegetables should be avoided “until the definitive source of the outbreak has been identified.”

Describing the preliminary results of two more epidemiological studies, RKI said 46 patients with HUS or EHEC infection from Bremen, Hamburg and Lubeck were questioned in detail from May 29 to June 2 about the foods they had eaten.

These cases were compared with 2,100 healthy individuals — the control group — matched for age, gender and region of residence. These were the results:

— Lettuce had been eaten by 84 percent of those ill, but only by 47 percent of the controls.

— Cucumbers had been eaten by 75 percent of those ill, but only 50 percent of the controls.

— Tomatoes had been eaten by 80 percent of those ill, but only 63 percent of the controls.

A total of 95 percent of those ill had eaten at least one of these vegetables.

In a second, separate study, investigators found that people who had eaten from the salad bar at a company canteen in Frankfurt were 7 times more likely to have developed bloody diarrhea than those who did not eat from the salad bar. There was no association with illness for other foods investigated, such as dessert, fruit and asparagus.

“These two unrelated and methodologically distinct studies support the results of the previously performed case control study,” RKI concluded, referring to an earlier epidemiological investigation conducted in Hamburg and published May 26.

And, sprouts were on the questionnaire.