The lethal E. coli bacteria that has left 18 dead and more than 1,500 sick in Europe is a new strain that experts have never seen before, the World Health Organization announced Thursday.
Early investigations suggest that the strain is an altered type of two E. coli bacteria with deadly genes that, experts said, could explain the widespread and dangerous nature of the illness.
"This is a unique strain that has never been isolated from patients before," Hilde Kruse, a food safety expert at the WHO, told The Associated Press. "[It has] various characteristics that make it more virulent and toxin-producing."
The source of the bacteria remains unknown, continuing to baffle experts.
The strain has hit eight countries in Europe, but has been concentrated in Germany.
Two cases have surfaced in U.S. hospitals, said Lola Russell, a spokeswoman for the Centers for Disease Control and Prevention. Russell did not disclose the names or locations of those who had fallen ill, but she did say their illnesses were associated with recent travel to Germany. Both are expected to survive.
Moreover, a local Texas health department confirmed Wednesday that seven cases of E. coli appeared in the Amarillo area this week, but Russell said those cases were not associated with the European outbreak.
Donna Makkhavane, a spokeswoman for the city of Amarillo, said that all seven cases were found in children, and "most were under 5 years old."
Makkhavane could not confirm the source of the E. coli outbreak in the children, but local experts are investigating food sources, international travel and exposure to animals.
Most E. coli strains are harmless, but those that do cause sickness usually trigger bouts of bloody diarrhea, fever and abdominal cramps. In the bacteria's most serious and severe form, the infection causes hemolytic uremic syndrome, or HUS, a condition that attacks the kidneys and can cause stroke, seizure, coma and death. In a typical outbreak, only about 1 to 2 percent of those affected experience HUS.
"Initial information suggests [the strain] is more virulent or "meaner" than those previously seen," said Dr. Christopher Ohl, associate professor of medicine in the infectious disease division at Wake Forest University School of Medicine. "Although we don't know how many total infections there are, it seems that it is more likely to result in HUS."
Despite a massive medical dragnet, the culprit for the outbreak has not yet been determined. Tomatoes, cucumbers and lettuce consumed in the region are being tested for the E. coli bacteria.
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, chairman 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."
And doctors said recent proposed budget cuts to the Food and Drug Administration's food surveillance program may make outbreaks in the U.S. even more likely in the future.
"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.
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 that is causing a higher percentage of people to experience HUS, or whether the outbreak is just extremely widespread.
Germany first targeted 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.