REUTERS/Tobias Schwarz Reinhard Burger, head of the Robert Koch Institute, addresses the media in Berlin on June 10, 2011. He says bean sprouts are the most likely source of the country's E.coli outbreak.

German officials announced on Friday that they believe bean sprouts are indeed the source of the deadly E. coli infections in that country, the worst such outbreak in recorded history.

Health authorities had previously fingered the sprouts, grown on an organic farm in Bienenbüttel south of Hamburg, but then retracted their decision when DNA tests comparing strains from infected patients and sprouts on the farm did not match.

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But now, says Reinhard Burger, head of Germany’s disease control agency, the weight of the investigative evidence points to a batch of sprouts grown on that farm. The New York Times reported:

Mr. Burger said investigators had examined 112 people, 19 of whom had been infected with E. coli during a group visit to a single restaurant, and had examined recipes for the food they had eaten, spoken to the chefs who prepared it and even examined photographs they had taken of one another with their choice of food on the table.

Those in the group who ate sprouts were nine times more likely to be infected than those who didn’t, leading investigators to believe sprouts were the source of the E. coli. The researchers traced the sprouts back to the organic farm in Bienenbüttel, and have shut down any further sales of products from the farm.

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“It was the sprouts,” Burger said at a press conference in Berlin. It’s likely, however, that the source of the outbreak will never be confirmed with absolute certainty.

The reason the genetic tests were negative may be because the originally contaminated sprouts are no longer available — they may have already been eaten or thrown away. Authorities said the E. coli could have been introduced to the sprouts by people, the water supply or the seeds. Whatever was contaminating the sprouts, public health officials hope, is long gone.

This means that tomatoes, cucumbers and lettuce, which were also initially suspected as possible sources of infection, are exonerated. Germany’s disease experts declared these produce safe to eat. They continued to advise people not to eat raw sprouts, however.

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So far, 30 people in Germany and one person in Sweden have died from E. coli infection, largely from complications involving hemolytic uremic syndrome, which can cause kidney failure. Nearly 3,000 people have been infected.

Update [2:30 p.m.]: If you don’t want to give up sprouts, you can still eat them; just cook them first. Here’s a good AP report on sprout safety.