The source of an alarming E. coli outbreak in Europe that has so far left 17 dead and more than 1,500 sick has baffled experts who warn the outbreak is more severe than anything they've ever seen from the bacteria.
The strain has hit eight countries in Europe, but has been concentrated in Germany.
Two cases have surfaced in the United States, said Lola Russell, a spokesperson for the Centers for Disease Control and Prevention. Russell did not disclose the victims' names or states where they reside, but she did say their illnesses are associated with recent travel to Germany. Both are expected to survive.
"This strain of E. Coli seems to be particularly virulent and also antibiotic resistant," said Dr. Ann Marie Kimball, professor of epidemiology and health sciences at the University of Washington School of Public Health. "It is a toxin producing strain which causes kidney shut down and apparently higher mortality."
Despite a massive medical dragnet, the culprit for the outbreak has not yet been determined. The initial suspect was cucumbers from Spain, but tests have discounted that the vegetable was responsible for carrying the bacteria. Tomatoes and lettuce are also being tested.
Because the source of the outbreak is still unknown, it is possible that tainted products could be unknowingly transported into the U.S., warned Dr. William Schaffner, chair of the department of preventive medicine at Vanderbilt University School of Medicine.
"Bacteria do not need a passport," said Schaffner. "There already have been a couple of cases in the U.S. The patients had traveled to Hamburg, returned to the U.S. where they became ill. This could happen again and the E. Coli could be transmitted to family, friends and others in the U.S."
Doctors say proposed budget cuts to the Food and Drug Administration's food surveillance may make outbreaks in the U.S. even more likely.
"I worry that the FDA is not properly resourced to be able to police imported food," said ABC News' senior health and medical editor Dr. Richard Besser. "This is so important for preventing the introduction of products that could be harmful."
E. Coli Outbreak Resistant to Antibiotics
But Schaffner said that it is not likely that this outbreak will spread to the U.S. because there is not a lot of fresh produce that is imported into the U.S. food supply from Europe.
Most E. Coli strains are harmless, but those that do cause sickness usually trigger bouts of diarrhea, fever and vomiting. In the bacteria's most serious and severe form, the infection causes hemolytic uremic syndrome, or HUS, a condition which attacks the kidneys and can cause stroke, seizure, coma and death.
German officials said this particular strain is a common bacteria found the digestive systems of mammals, including cows and humans.
In a typical outbreak, about 1 to 2 percent of those affected suffer from HUS. Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said that it will be important to decipher whether there is something unusual about this particular agent which is causing a higher percentage of people to suffer from HUS or the outbreak is just extremely widespread.
Germany first accused cucumbers imported from Spain as the source of the outbreak. After experts tested the vegetables and they came up negative for carrying the bacteria, Spain threatened to sue Germany over the cucumber charge.
But Osterholm said Spain may not be in the clear.
"Spain has no basis to say the cucumbers weren't involved because this is such a difficult organism to find," said Osterholm. "Right now, there is a lot of misinformation out there because, even if a food item is tested, there can be such a low level of contamination that nothing ever comes up in testing."
Osterholm continued to say that experts need to look epidemiologically at these cases to compare what E. Coli sufferers ate versus what the non-E. Coli sufferers consumed.
"Once you identify products, you do the trace and it almost universally comes back to one source," said Osterholm.
Kimball noted that strain "seems to be affecting a different age group."
Usually, young children and elderly people are most at risk of severe E. Coli symptoms, but women of various ages seem to be hit hardest by the outbreak.
"If you look at the primary group that eats salads in the U.S. and around the world, it's young to older women," he said. "The profile of the outbreak hit perfectly. It wasn't a surprise to see that vegetables were implicated."