The German authority said on Friday bean sprouts were probably the source of the E. coli outbreak, which has killed 30 people and infected about 3,000 around the world.

"It's the (bean) sprouts," said Reinhard Burger, president of the Robert Koch Institute (RKI), Germany's national disease control center.

"People who ate (bean) sprouts were found nine times more likely to have bloody diarrhoea or other signs of E. coli infection than those who did not," He said

But he admitted this conclusion was based on epidemiological investigation, as no positive result has been found through sample tests.

According to the data of RKI, more than 1,000 sample tests focusing on bean sprouts have been done so far.

He also said the Robert Koch Institute was lifting its warning against eating cucumbers, tomatoes and lettuce but keeping the warning in place for the sprouts.

This is the second time bean sprouts were identified as the source for the terrible outbreak. The German authority first issued warning on it last Sunday, which was overthrown by laboratory tests on Monday.