Derry Dunn considers himself lucky. If the Orange County justice of the peace had waited a little longer to begin treatment, he could have been among the 30 to 40 percent of victims who lose their limbs due to a bacterium that causes a flesh-eating disease. Dunn is one of the more than 20 cases that doctors see every year on the Texas Gulf Coast, said Dr. A. Scott Lea, assistant professor of infectious diseases at UTMB here. "In Galveston, we see it four or five times a year," Lea said. "We've seen two this year already." In about half the cases, doctors don't get to the patient soon enough. About 10 percent of vibrio patients die, Lea said, and 30 to 40 percent lose a limb. "If you are really lucky, you only lose some skin and tissue," the UTMB doctor said. Although it triggers a vicious disease, it affects only a tiny fraction of the hundreds of thousands of people who get wet in the Gulf of Mexico every year. Lea said that a sure sign of the disease would be purple blisters, compared to other blisters that are usually yellow in color. "The doctors along the coast are pretty adept at diagnosing it," Lea said. "It's when the patient goes back to North Texas or Central Texas or wherever they came from and the doctor doesn't recognize it, that it can really be a problem."