A trans-European war of the vegetables has seen Russia barring fresh agricultural produce from the European Union and more cross-border bans are in force across the EU.
EU envoys Friday sought to ease diplomatic tensions over the outbreak. Spain said it would seek damages for the slur cast on its produce after Germany slapped a ban on Spanish cucumbers.
Scientists remained divided over early reports that organic cucumber grown in Spain could be the cause of the new strain of E. coli bacteria unknown to the World Health Organization scientists.
Rowland Cobbold, a veterinary public health researcher at the University of Queensland in Australia, told Bloomberg News the origins of the bacteria, which caused a rare and potentially deadly kidney disease, may be traced to cows, not cucumbers.
"The cucumber may be the lead back to the original ruminant that was the source," Cobbold said.
The bacterium has a tendency to mutate, not seen in earlier strains, which binds it to the intestine where it produces a deadly toxin.
Infections rose overnight by more than 200 to a total of 1,700 and could likely rise amid continuing unrestrained travel between Europe and the rest of the world. The three U.S victims had recently travelled to northern Germany.
The deadly food bug in Germany has killed more people and resulted in more cases of severe kidney damage than any other on record, Robert Tauxe at the U.S. Centers for Disease Control and Prevention in Atlanta, said in comments reported by the London Daily Mail newspaper.
Asked if this was the world's deadliest E. coli outbreak yet, Tauxe said, "I believe it is,"
the newspaper reported.
"This is an unprecedented outbreak in its size," microbiologist Hugh Pennington told the Australian Broadcasting Corp. "It's not quite the biggest ever, in terms of number of cases, but it certainly is the biggest in terms of the health impact, the number of cases of people with complications. And I'm afraid it will probably be the biggest in terms of number of deaths as well."
As the diplomatic row over the cause of the infection deepened, Russia took a swipe at the European Union, mocking its health standards and announced it would bar all fresh vegetables from the EU.
Russian consumer protection agency head Gennady Onishchenko said that orders to stop all incoming European vegetable shipments had gone to all customs checkpoints, the BBC reported.
"I call on people to forgo imported vegetables in favor of domestic products," Onishchenko said.
"This shows that Europe's lauded health legislation -- one which Russia is being urged to adopt -- does not work," he said.
Reinhard Burger, president of the Robert Koch Institute, the German public health body tackling the E. coli outbreak, says it could be months before the problem eases, depending on whether infected food is still in warehouses and whether the original source is still active.
He told the BBC "we may never know" the infection's source.