(CNN) -- An outbreak of a virulent strain of E. coli has killed 19 people in Europe and infected more than 2,000 in at least 12 countries, the World Health Organization said on Saturday.

All but one of the fatalities were reported in Germany, where officials say it's still too early to determine whether the peak of the outbreak has passed. One person in Sweden also died.

In Germany, there have been 573 cases of hemolytic uremic syndrome (HUS) -- a form of kidney failure -- in the current European outbreak, according to WHO. That's more cases of HUS than in any other recorded outbreak, worldwide.

Twelve patients in Germany have died of HUS, according to WHO, while six died of enterohemorrhagic E. coli, EHEC, a strain that causes hemorrhaging in the intestines and can result in abdominal cramps and bloody diarrhea.

Reports indicate that an estimated 1,428 people have that E. coli strain so far but do not have HUS, according to the World Health Organization.

Infections have also been identified in Austria, Czech Republic, Denmark, France, Netherlands, Norway, Poland, Spain, Switzerland and the United Kingdom, according to the organization.

The European Food Safety Alert Network initially said enterohemorrhagic E. coli was found in organic cucumbers originating from Spain, packaged in Germany and distributed to various countries. But authorities have said that the source of the contamination has not been pinpointed.

The Robert Koch Institute, Germany's federal unit responsible for disease control and prevention, has advised German consumers not to eat raw tomatoes, cucumbers and lettuce.

Cucumbers, tomatoes and lettuce imported from Germany and Spain will be tested and cleared before they are sold in the United States, according to David Elder of the Food and Drug Administration, and those test results will be shared with the European Union.

Germany and Spain account for a small fraction of produce that is sold in the United States in a given year.

Two women and a man who traveled last month to northern Germany remain hospitalized in the United States with HUS, Chris Braden of the U.S. Centers for Disease Control and Prevention said Friday. 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.