In a study of 23 women with recurrent infections, the researchers found that most patients were being reinfected by the same strain of E. coli bacteria that caused their initial infection and not by different strains each time, as reported previously. In addition, they found that the bacteria causing recurrences in most of the women were harbored in the patient's own intestinal tract.

Results of the study were reported in the August Journal of Infectious Diseases.

"These findings give us a new understanding of the mechanism of recurrent urinary-tract infections," said Thomas A. Russo, UB assistant professor of medicine and lead investigator on the study.

Most women with urinary tract infections are treated with a short course of antibiotics designed to kill the bacteria in the urine. This may no longer be the best approach, given the study's results, he said, because while such therapy clears up the infection in the urinary tract, it doesn't kill the same bacteria existing in the fecal flora, ready to infect again.

"It's possible that alternative approaches aimed at eradicating a persisting strain from the intestinal flora, and not just the urinary tract, would result in a long-lasting permanent cure," Russo said.

Urinary-tract infections in women account for an estimated 7 million office visits a year, at a cost of more than $1 billion. About 20 percent of women with an initial infection will develop recurrences, some as many as 20 a year.

Previous studies concluded that more than 75 percent of the recurring infections were caused by a new strain of bacteria from an outside source. Using a technique similar to DNA fingerprinting unavailable to earlier researchers, Russo's group found that 68 percent of recurring infections in the 23 young women were caused by the same strain of bacteria that caused their first infection.

Further analysis determined that the recurrences were new infections, and were not caused by bacteria that persisted from the previous infection. The researchers traced the new infections to bacteria harbored in the patient's own colon. "If our results are confirmed in future studies, they may have significant therapeutic implications for some or all women with recurrent UTIs," Russo stated.

"Data from at least two previous treatment studies suggest that long-term remission can be achieved with antimicrobials in some women. We also know that certain antibiotics can eradicate bacteria in the fecal flora better than others. Further data on the impact of different treatment regimens on long-term cure clearly are needed."

Others participating in the study were Ann Stapleton, Thomas M. Hooton and Walter E. Stamm of the University of Washington, Seattle, and Suzanne Wenderoth of the National Institutes of Health.