CHICAGO, May 18 (Xinhua) -- Travelers to and children in underdeveloped areas of the world with blood type A suffer more severe symptoms once infected with diarrhea than those with blood type O or B, a study led by researchers at Washington University School of Medicine in St. Louis shows.

Enterotoxigenic E. coli are responsible for millions of cases of diarrhea and hundreds of thousands of deaths every year, mainly of young children. Some people infected with the bacterium develop severe, cholera-like, watery diarrhea that can be lethal; while others just experience unpleasant symptoms but recover easily, and some don't get sick at all.

The researchers then investigated whether blood type influences the disease severity by giving healthy volunteers a dose of an E. coli strain originally isolated from a person in Bangladesh with severe, cholera-like diarrhea.

They observed the volunteers for five days, and obtained data and blood samples from 106 people, and found that people with blood type A got sick sooner and more seriously than those of other blood types.

More than eight out of 10 or 81 percent of blood group A people developed diarrhea that required treatment, as compared with about half of people with blood group B or O.

The researchers also found that the bacteria produce a specific protein that sticks to blood A-type sugars, but not blood B- or O-type sugars on intestinal cells. Since the protein sticks to E. coli as well, it effectively fastens the bacteria to the intestinal wall, making it easy for them to deliver diarrhea-causing toxins to intestinal cells.

The effect of blood group in people infected with this strain of E. coli was striking and significant, but it doesn't mean people should change their behavior based on blood type, the researchers said.

The study was published in the Journal of Clinical Investigation Thursday.