(CNN) -- Despite complaints from Europeans, Russia will keep intact its ban on vegetables from the European Union because of the outbreak of a rare strain of E. coli, Russian Prime Minister Vladimir Putin said Friday.
The European Union has told Russia that the ban contradicts the spirit of the World Trade Organization.
"We can't poison our people for the sake of some spirit," Putin retorted.
The E. coli infection has spread to 12 countries and is blamed for at least 18 deaths -- all but one reported in Germany. About 1,800 others have been sickened.
There have been 552 cases of hemolytic uremic syndrome (HUS) -- a form of kidney failure -- in the current European outbreak, according to the World Health Organization. That's more cases of HUS than in any other outbreak ever worldwide, according to an official at the U.S. Centers for Disease Control and Prevention.
Eleven patients in Germany have died of HUS, according to WHO. Six died of enterohemorrhagic E. coli, EHEC, a strain that causes hemorrhaging in the intestines and can result in abdominal cramps and bloody diarrhea.
One person in Sweden also has died.
Across Europe, 1,271 cases of EHEC without HUS have been reported, WHO said on its website.
Although the outbreak's cause has not been confirmed, cucumbers, tomatoes and lettuce imported from Germany and Spain will be tested before they are sold in the United States, according to David Elder of the U.S. Food and Drug Administration.
"I want to emphasize that this outbreak has not affected the U.S.," Elder told reporters in a conference call. "Produce remains safe and there is no reason for Americans to alter where they shop, where they buy or what they eat."
Two women and a man who traveled last month to northern Germany remain hospitalized in the United States with HUS, said Chris Braden of the U.S. Centers for Disease Control and Prevention. A fourth person developed bloody diarrhea, but was not hospitalized, he added.
Two U.S. service members in Germany also developed diarrhea, Braden said. "We have no expectation that this will spread in our country," he added.
In addition to cases in Germany, Sweden and the United States, cases have been identified in Austria, Czech Republic, Denmark, France, Netherlands, Norway, Spain, Switzerland and the United Kingdom, according to WHO.
All but two of the cases occurred in people who had recently visited northern Germany or, in one case, had contact with a visitor from northern Germany, the organization said.
Russia's ban on fresh vegetable imports is the strictest response to the outbreak.
Putin said that despite the complaints from European officials, who see the move as disproportionate, "cucumbers that cause human fatalities are indeed smelling bad."
"We expect that our partners at least tell us about the source of this infection, but they themselves can't figure out what's going on," he said.
Russia plans to check on the validity of the ban, he said, but not until more facts emerge from the European Union about the outbreak.
Scientists at the Beijing Genomic Institute have said the outbreak of infection in Germany is caused by a new "super-toxic" E. coli strain, though the CDC said the strain has been seen before, particularly in a 2009 outbreak in the republic of Georgia.
"We have very little experience with this particular strain, but it has been seen before," said Robert Tauxe, deputy director of the CDC's division of food borne diseases.
WHO said the strain has been seen before, but not with an EHEC outbreak.
The CDC said the strain is rare and added that, while it is not aware of any cases ever having been reported in the United States before, it is aware of a few previous reports of the strain in other countries. Britain's Health Protection Agency has said that the strain suspected in the outbreak is "rare" and "seldom seen in the UK."
Yelena Skrynnik, Russia's agriculture minister, issued a statement Thursday assuring Russians that, despite the ban, "the volume of home-grown vegetable production combined with exports (from other countries) is sufficient to fully meet Russia's domestic demand."
In 2010, the imports of tomatoes and cucumbers from the EU amounted to, respectively, 11% and 5% of all imports of those vegetables into Russia, the Russian Agriculture Ministry said.
The ban could potentially affect some larger cities in the European part of the country, where about 90% of vegetables are imported, said Sergey Shugayev, chairman of the Rural Russia Association.
China and Turkey are the two largest exporters of fresh vegetables to Russia, according to the Russian Greenhouses Association.
The European Food Safety Alert Network initially said EHEC was found in organic cucumbers originating from Spain, packaged in Germany and distributed to various countries. But authorities have said the source has not been pinpointed.
Spain's Ministry of Health, Social Politics and Equality said Thursday that all samples of Spanish produce that it analyzed had proved negative.
CNN's Maxim Tkachenko contributed to this report.