The first tests on bean sprouts from a German farm suspected of being the source of the outbreak were negative.

Of 40 samples examined from the farm in Uelzen, south of Hamburg, the first 23 tested negative, officials said.

More than 2,200 people have fallen ill in 12 countries. Cases outside Germany have been linked to travel there.

Initially, German officials had pointed to Spanish cucumbers as the likely cause, but that later proved false.

In Luxembourg, the EU agriculture ministers will want to know how close experts are to identifying the source, amid mounting criticism of the investigation into the outbreak.