(AP) -- Salad eaters, beware. Experts say it's little surprise that sprouts are behind the world's deadliest E. coli outbreak.
Sprouts need warm and humid conditions to grow - precisely the same conditions required by bugs like E. coli and salmonella to thrive. And raw sprouts have been blamed before in food poisoning outbreaks, in the U.S. and a large outbreak in Japan in 1996.
German officials said Friday that sprouts caused the deadly outbreak there, although they don't know which kind. The organic farm linked to the outbreak grew a wide variety, including alfalfa, onion and radish.
Sprouts are grown in water from seeds, which are rinsed daily. They can be grown from numerous kinds of vegetables and are often eaten raw in salads and sandwiches.
Officials in Germany say they're not yet sure whether the sprout seeds were infected or whether the sprouts got contaminated by dirty water. Public health agencies have long been concerned about the risks of bacterial contamination of water used to produce sprouts.
E. coli can stick to the surface of sprout seeds.
"They can lay dormant on the seeds for months," said Stephen Smith, a microbiologist at Trinity College in Dublin.
Unfortunately for sprout-eaters, the germs are then inside the sprout as well as outside.
At that point, "washing has no effect," Smith said.
The European Food Safety Authority doesn't recommend avoiding certain foods, but advises consumers to take basic precautions, like washing all fruits and vegetables with clean water and peeling or cooking them when possible.
For now, German authorities are recommending people avoid all sprouts.
In the U.S., the Food and Drug Administration recommends children, the elderly, pregnant women and people with weakened immune systems avoid eating any kind of raw sprouts. The agency also recommends cooking sprouts thoroughly to reduce the risk of illness.
Because most sprouts - including alfalfa, bean, and mung - are eaten raw, they're not exposed to temperatures high enough to kill bacteria.
But experts say it's not necessary to ditch sprouts entirely because they are a good source of protein and vitamins.
"It's not that all sprouts are bad," Smith said. "But if you're desperate to eat sprouts and you want to be safe, try stir-frying them first."
Bob Sanderson, president of the U.S.-based International Sprout Growers Association, said the industry is working to update food safety guidelines issued by the FDA more than a decade ago. Sanderson's group - which represents 45 producers around the world - named June "Sprout Health and Wellness Month."
"In a way, it is kind of international sprout month," he said. "Just maybe not in the way we hoped."