In the study, published in today's (Thursday, Oct. 4) New England Journal of Medicine, researchers analyzed the records of female students at UC Berkeley, the University of Minnesota, and the University of Michigan. The women had come into university health centers for treatment of urinary tract infections, or UTIs.

The fact that the bacteria emerged in different parts of the country suggests that the source of the strain may have been introduced through contaminated foods, said Lee Riley, MD, professor of epidemiology and infectious diseases at UC Berkeley, and principal investigator of the study.

"Urinary tract infections are not considered epidemic infections," said Riley. "The only way this (community-acquired infection) could happen is if it's spread by a contaminated product."

A bladder infection, or cystitis, occurs when bacteria such as E. coli get into the urethra, or urinary canal. People with bladder infections often experience frequent and painful urination.

Bacteria was isolated from more than 300 urine samples and tested for resistance to different antibiotics commonly used to treat bladder infections.

The study found that 22 percent of the E. coli strains collected from the UC Berkeley site were resistant to trimethoprim-sulfamethoxazole, a first-line antibiotic used to treat bladder infections. Further tests revealed that 38 to 50 percent of the drug-resistant forms of cystitis from these three geographical regions were caused by a previously unrecognized strain of multidrug-resistant E. coli called clonal group A.

"We were really surprised to find so many unrelated women with UTIs caused by the same organism," said Amee Manges, a doctoral student at UC Berkeley's School of Public Health and lead author of the study.

It is possible for humans to acquire drug-resistant bacteria through the foods they eat, said UC Berkeley's Riley. He said the practice of giving animals antibiotics to protect them from disease may be leading to the emergence of drug resistance in food products, which could pose a serious public health issue for humans.

Researchers also compared the bacteria from the urine samples with fecal bacteria in stool samples taken from 41 healthy people from the UC Berkeley community. They were able to identify the same clonal group A strain of E. coli in the fecal samples, suggesting that the strain exists in that community.

"This clonal group of E. coli was responsible for 11 percent of all UTIs at the UC Berkeley site, and was responsible for half of the trimethoprim-sulfamethoxazole resistant UTIs during the four-month period of the study," said Manges. "It's clear this clonal group is really influencing the resistance rates we are observing among UTI cases here."

The authors point out that the United States has seen an increase in recent years of drug-resistant forms of UTI. Some studies suggest that as many as 18 percent of women in the United States with urinary tract infections are resistant to trimethoprim-sulfamethoxazole.

Urinary tract or bladder infections are second only to respiratory infections in prevalence. According to the National Institutes of Health, UTIs accounted for nearly 8.3 million doctor visits in the United States in 1997.

Women are at greater risk for urinary tract infections; about one in five will develop at least one bladder infection in her lifetime. Factors contributing to the increased risk for women compared to men may include a shorter urethra, which gives bacteria easier access to the bladder, and a urethral opening that is anatomically close to sources of bacteria from the vagina and anus.

People with diabetes or weakened immune systems are also at risk for infections, as are people with catheters inserted into their bladders for health reasons.

Other authors of the study are James R. Johnson, M.D., and Timothy T. O'Bryan of the University of Minnesota; Betsy Foxman, Ph.D., of the University of Michigan; and Kathleen E. Fullerton, M.P.H. of UC Berkeley.