Health experts around the globe are keeping a close eye on the deadly E. coli outbreak in Europe—including here in the United States.

The Centers for Disease Control and Prevention is closely following the large outbreak of Shiga toxin-producing E. coli O104, or STEC O104, infections which are centered in Germany.

The Robert Koch Institute, Germany’s disease control and prevention agency, said Wednesday that 470 people are now suffering from hemolytic uremic syndrome, or kidney failure, a life-threatening complication of E. coli infections. That’s up from 373 cases reported Tuesday.

As far as U.S. citizens who have traveled to Europe, the CDC said two cases of HUS have been reported “in persons with recent travel to Hamburg, Germany.”

However, the agency said they are still awaiting lab results to confirm if these cases are directly related to STEC O104. 

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Hemolytic uremic syndrome (HUS) is a condition that results from premature destruction of red blood cells in the body, the Mayo Clinic said on its website. The damaged cells then drift and clog the filtering system in the kidneys, in many cases causing kidney failure.

Most cases of HUS occur in children as a result of certain strains of E. coli, but can also happen in adults. Often the cause of the condition in adults is unknown. Symptoms include bloody diarrhea, vomiting, abdominal pain and fever. HUS is considered a serious condition, but can be cured with appropriate treatment.

CDC officials said this deadly strain of E. coli spreading across Europe is very rare – and they are not aware of any cases of STEC O104:H4 infection ever being reported in the United States.

The exact source is still not known, but scientists said the suspicions about vegetables or salads being a possible source are well-founded since cattle manure used in fertilizer can harbor E. coli.

"E. coli can attach to the surface of many fresh produce, such as lettuce leaves, spinach leaves and cucumber. These type of E.coli survive harsher environmental conditions than...and produce some nasty toxins to humans," said Brendan Wren of the London School of Hygiene & Tropical Medicine.

The outbreak, which started in mid-May, has so far sickened more than 1,000 people in Germany as well as people from Spain, Sweden, Britain, Denmark, France and the Netherlands who had recently been in Germany.

It's "extraordinary" to see so many cases of the kidney complication from a foodborne illness, said Dr. Robert Tauxe, a foodborne disease expert at the CDC. "There has not been such an outbreak before that we know of in the history of public health."

He added there have been several high-profile foodborne outbreaks in recent years, but none with such a high death toll.

CDC Q&A:

Q: Would this be the largest E. coli outbreak ever in the world?

A: We are still learning more about the overall size of this outbreak. The number of HUS cases involved indicates that the outbreak is very large.

Q: Tell us about this rare strain, and are we testing for it here?

A: A very rare strain of Shiga toxin-producing E. coli, or STEC has been reported from some patients in the outbreak. This strain, E. coli O104:H4 has never been seen in the United States, and the CDC is only aware of few reports of this strain from other countries. Although it is rare, the United States’ public health surveillance systems are designed to be able to identify this, and other rare STEC strains, in ill people. However, the ability to detect STEC infections through surveillance depends on proper diagnostic testing of patients presenting with symptoms suggestive of STEC. In 2009, CDC published recommendations for the diagnosis of STEC infections by clinical laboratories.

The illness that it causes is similar to that caused by E. coli O157:H7 which is also a Shiga toxin-producing E. coli and the one most commonly identified in the United States.

Q: Could people travel from Germany and spread it here?

A: STEC infections can be spread from person to person. The best defense is careful, thorough hand washing. Persons returning from Germany who have diarrhea should be sure to wash hands well with soap and warm water after using the bathroom, and should not prepare food for others while they are ill. People who are in contact with ill people who recently visited Germany should also follow basic hygiene practices carefully, including washing their hands thoroughly before eating or drinking and after caring for an ill person.

Q: Why are so many people sick?

A: It is too early to know why this is such a large outbreak. The large size may have to do with contamination of a popular food item. However, to our knowledge a specific food vehicle has yet to be confirmed. It is also possible that the unusual strain is particularly likely to cause HUS.

Anyone who has recently traveled to Germany, and is exhibiting signs or symptoms of HUS, should immediately seek medical attention.

Reuters contributed to this report.