Some vacationers may be more lucky than others if they catch a case of "traveler's diarrhea."
Researchers found that for people infected with the type of E. coli bacteria that causes the condition, the severity of their symptoms seemed to depend on their blood type.
Enterotoxigenic E. coli causes millions of cases of diarrhea and hundreds of thousands of deaths every year worldwide. Most of those affected by the bacteria are young children and those visiting developing countries.
Some people infected with this type of E. coli develop severe, watery diarrhea. For others, the infection causes only mild symptoms or none at all.
It turns out that blood type might play a part.
People with type A blood were more likely to develop severe diarrhea when infected with this specific type of E. coli than those with type O or B blood, the study authors reported.
Researchers at Washington University School of Medicine, along with scientists at Johns Hopkins University, the U.S. National Institutes of Health and the Naval Medical Research Center, said they pinpointed the protein responsible for this discrepancy among blood groups.
They found that E. coli releases a protein that sticks to intestinal cells in people with type A blood, but not those with type O or B blood. The protein also sticks to the E. coli, making it easier for the bacteria to infect healthy cells.
The study authors said the goal is to find a vaccine that targets this protein and protects those with type A blood.
"We think this protein is responsible for this blood-group difference in disease severity," said study senior author Dr. James Fleckenstein, an associate professor of medicine at Washington University, in St. Louis.
"A vaccine targeting this protein would potentially protect the individuals at highest risk for severe disease," he added in a university news release.
In the controlled trial, researchers gave healthy volunteers a dose of an E. coli strain originally isolated from a person in Bangladesh who had severe diarrhea. The volunteers were monitored for five days. Those who developed moderate to severe diarrhea were treated with antibiotics.
At the end of the trial, all of the participants were given the medication to clear the bacteria from their system -- even if they didn't get sick.
Interestingly, after analyzing data and blood samples collected from 106 people who participated in the trial, the researchers found that those with blood type A got sick sooner and more seriously than those with other blood types.
The trials showed that 81 percent of those with type A blood developed diarrhea that required treatment. The same was true for only about 50 percent of those with type B or O blood.
Despite these findings, the researchers don't suggest that people change their behavior based on their blood type.
"I don't want anyone to cancel their travel plans to Mexico because they have type A blood," said researcher Dr. Matthew Kuhlmann. "Or the converse: I don't want anyone to think they're safe because their blood group is not A. There are a lot of different species of bacteria and viruses that can cause diarrhea, so even though this blood-group association is strong, it doesn't change your overall risk. You should continue taking the same precautions whatever your blood type."
Those precautions include frequent hand washing, using purified water and practicing overall good hygiene as the best way to protect against E. coli.
The study, funded by the U.S. National Institutes of Health, was published May 17 in the Journal of Clinical Investigation.
FoodSafety.gov has more information on E. coli.
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