Two U.S. residents who recently traveled in northern Germany appear to be among victims of a massive outbreak of food poisoning that has killed 16 and sickened more than 1,150 people in Europe since the second week of May, federal health officials confirmed Tuesday.
The victims have been hospitalized with serious, life-threatening complications of E. coli infections caused by a rare strain of the bacteria that has taken scientists by surprise, said Dr. Robert Tauxe, deputy director of foodborne, bacterial and mycotic diseases at the U.S. Centers for Disease Control and Infection.
"We have never seen that organism before," Tauxe told msnbc.com.
He's referring to E. coli 0104:H4, a strain that can cause many of the problems of the better-known E. coli 0157:H7, including bloody diarrhea and the potentially deadly hemolytic uremic syndrome, or HUS.
The U.S. victims, who have not been identified by name, state or geography, were reported by state health officials who are monitoring illness surveillance systems for signs that the outbreak has made its way from Europe to America. Investigation of their cases is continuing, Tauxe said.
State health agencies have been directed to report instances of HUS or bloody diarrhea in recent travelers to Germany. Meantime, officials with the federal Food and Drug Adminstration say they're flagging cucumbers, lettuce and tomatoes from Spanish growers implicated in the outbreak for further inspection.
"Luckily, this is not a huge import season for vegetables," said Siobhan DeLancey, an FDA spokeswoman.
Tauxe and other food safety experts said they would expect cases to expand beyond Germany and eight other European nations to the U.S.
"It's hard for me to believe there won't be a handful of travelers who ate contaminated food in a restaurant," said Dr. Dennis Maki, an infectious disease expert and professor emeritus at the University of Wisconsin Department of Medicine. "I'll be surprised if we don't have a few cases."
Victims likely become ill within days of eating contaminated food, Maki said. Travelers who find themselves on a plane or other public transport with diarrhea and other food poisoning symptoms should remember to wash their hands thoroughly and clean surfaces as they go. There is a small risk of person-to-person spread of the infection, mostly among children and those who care for them.
The rare germ, which is a type of bacteria known as Shiga-toxin producing E. coli, or STEC, appears to be resistant to many commonly used antibiotics, said Tauxe. However, doctors typically try to stay away from antibiotics in STEC cases. Because HUS causes kidney failure and acute anemia, victims are typically treated with dialysis and other emergency measures.
"It takes a lot of support care," Tauxe said.
It's not yet clear whether this strain of E. coli is more virulent than others, or whether there are massive numbers of milder cases that went undetected, Tauxe added.
Germany's top health official said 373 people have come down with HUS, in which E. coli attacks the kidneys, often requiring critical care. Another 796 people in the country have been hit by less serious infection with the E. coli bacteria. The northern city of Hamburg and surrounding areas have been worst affected.
In a typical year, Germany might see 60 cases of HUS, officials said.
Investigators in Europe continued to scramble Tuesday to detect the source of the unprecedented outbreak that has been tied to raw cucumbers, lettuce or tomatoes. European Union officials said Germany identified cucumbers from the Spanish regions of Almeria and Malaga as possible sources of contamination. Another suspect batch may have orginated in the Netherlands or Denmark.
The vegetables could have been contaminated at any point on the journey from field to retail outlets. E. coli is found in the digestive systems of cows, humans and other mammals and can be spread through fecal contact. In the vast majority of cases, it causes mild stomach problems.
Though FDA officials are flagging incoming produce from Spain for infection, they don't expect huge quantities of vegetables. In all of May, for instance, the U.S. imported one shipment of Spanish cucumbers, or 480 cases. So far, there is no indication that the shipment was contaminated, DeLancey said.
The vast majority of E. coli infections have affected either Germans or people who recently traveled to Germany. Other cases have been reported in Denmark, France, the Czech Republic, the U.K., the Netherlands and Switzerland but the World Health Organization said it only had confirmation of the German cases and another six cases in France.
Follow health reporter JoNel Aleccia on Twitter @jonel_aleccia