BERLIN - Specialists in high-tech labs tested thousands of vegetables as they hunted for the source of the world's deadliest E. coli outbreak, but in the end it was old-fashioned detective work that provided the answer: German-grown sprouts.
After more than a month of searching, health officials announced Friday they had determined that sprouts from an organic farm in the northern German village of Bienenbuettel were the source of the outbreak that has killed 31 people, sickened nearly 3,100, and prompted much of Europe to shun vegetables.
"It was like a crime thriller where you have to find the bad guy," said Helmut Tschiersky-Schoeneburg, head of Germany's consumer protection agency.
It's little surprise that sprouts were the culprit - they have been implicated in many previous foodborne outbreaks: ones in Michigan and Virginia in 2005 and a large outbreak in Japan in 1996 that killed 11 people and sickened more than 9,000.
While sprouts are full of protein and vitamins, their ability to transmit disease makes some public-health officials nervous. Sprouts have abundant surface area for bacteria to cling to, and if their seeds are contaminated, washing won't help.
"E. coli can stick tightly to the surface of seeds needed to make sprouts, and they can lie dormant on the seeds for months," said Stephen Smith, a microbiologist at Trinity College in Dublin, Ireland.
Once water is added to make the seeds grow, the number of bacteria carried within the seeds can multiply up to 100,000 times.
German investigators tracked the path of the bacteria step by step, from hospital patients struggling with diarrhea and kidney failure, to restaurants where they may have gotten sick, to specific meals and ingredients, to industrial food suppliers and the farms that grew the produce.
And they still have more questions to answer, such as what contaminated the sprouts in the first place? Bad seeds, contaminated water, nearby animals, the answer is still elusive.
Interviews with thousands of patients - mostly women between ages 20 and 50 with healthy lifestyles - led investigators to conclude initially that salads could be the problem.
Health officials immediately warned consumers to avoid cucumbers, tomatoes, and lettuce - causing huge losses to European farmers as demand plummeted for their produce - but the seemingly ubiquitous alfalfa, radish, and other sprouts weren't yet on anyone's radar.
"You get this stuff in every cafeteria," said Gert Hahne, spokesman for the agriculture ministry in Lower Saxony, the state where the contaminated sprouts were found. "But after two weeks of diarrhea, most people don't remember if they had a few sprouts on top of a ham sandwich or mixed into a salad."