In Brussels, the European Commission, the European Union’s executive arm, defended its decision to broadcast an apparently inaccurate German warning about Spanish cucumbers.

Under EU food safety rules, any member state that believes it is being affected by a health issue with a possible European dimension is obligated to pass that information to the Commission. The Commission then disseminates it to other national governments.

John Dalli, the health commissioner, said the system worked as it was supposed to, but that he would review the episode to see if there were lessons to be learnt for the future. Privately, other officials argued that they were relying on the best available information at a time of mounting fatalities. “We had people dying,” one said.

The Commission is exploring ways to provide EU aid to stricken farmers, although officials said their options were legally limited and that most of the money would probably have to come from national governments – a difficult prospect at a time when Spain and other member states are undertaking harsh budget cuts.

Philippe Binard, head of Freshfel, the European Fresh Produce Association, an industry trade group, said his members were urging authorities to speed up the investigation.

“The market is in a complete standstill in most of the European member states,” Mr Binard said, noting the threat by Russia – the EU’s largest produce export market – to impose a blanket ban unless the situation was clarified. Similar messages were coming from Ukraine, Belarus and the Gulf states, he said.

But as farmers’ losses piled up, the source of contamination remained a mystery. Officials described a shoe-leather investigation in which German health officials were asking hundreds of patients – some gravely ill – to try to recall what they had eaten over the last 10 days, and then comparing results.

“We don’t have a clue at this stage where the contamination is coming from,” one European official said. Another raised the possibility that a definitive cause might never be found – an outcome that could loom over the European vegetable industry long after the outbreak has passed.

Mr Binard also acknowledged the difficulty of pin-pointing irregularities in an extensive modern food chain that stretches from farms to consumers. “The chain has a lot of operators,” he said, from regional packing stations, to wholesale markets, processing plants, catering facilities and supermarkets, among others.

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