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Outbreaks of Resistant E. coli Strain Prompt Concern

Urinary infections could be caused by contaminated food, says study

WEDNESDAY, Oct. 3, 2001 (HealthDayNews) -- A new strain of an antibiotic-resistant bacterium that causes urinary tract infections in women has suddenly appeared in widely separated communities in the United States, raising the possibility of widespread contamination of food, researchers report.

The Escherichia coli strain has been isolated from women with urinary tract infections in California, Michigan and Minnesota, reports a team led by Dr. Lee W. Riley in the latest kissue of The New England Journal of Medicine. Riley is a professor of epidemiology and public health at the University of California at Berkeley. The strain is resistant to the trimethoprim-sulfamethoxazole combination commonly used to treat E. coli infections and has a genetic fingerprint different from other resistant strains, the researchers report.

"This one is different from other groups of E. coli that are traditionally associated with urinary tract infections," says Riley. "We provide evidence that this drug-resistant strain might be spread by food."

The emergence of the new strain in three different geographic areas points toward "one or more contaminated products ingested by community residents," the journal report says. Contaminated foods have been responsible for community-wide outbreaks of intestinal infections caused by a different strain of E. coli that is designated 0157:H7, the report says.

The public health implications of the finding could be important. The new strain accounts for a startlingly large percentage of antibiotic-resistant E. coli above what normally would be expected in the areas where it has been found.

"If it were not for this clone [strain], the overall level of resistance in the Berkeley population we studied would be 12 percent," Riley says. "Because of this clone [strain], it is 22 percent. In Minnesota, a related strain accounts for a similarly large proportion of antibiotic-resistant infections."

The finding is important for two reasons, says Dr. Walter E. Stamm, professor of medicine at the University of Washington School of Medicine and author of an accompanying editorial.

"First, it is a demonstration of the continuing development of antibiotic resistance," Stamm says. "It is also possible that there might be a potential single source of this organism, possibly in food."

Further tests to determine the breadth of the outbreak are needed, as are studies of possible sources of the infection, Stamm says. Riley says he is trying to determine that source.

Whatever the source, "it is probably a very likely thing that the overuse of antibiotics plays a role in the emergence of such resistant strains," Stamm says. His editorial says it is "yet another example of the ongoing global problem of antimicrobial resistance."

That problem is due not only to medical overuse of antibiotics, Riley says. The food industry also uses a lot of antibiotics, he says. "Half of all the antibiotics used in the United States is given to animals as growth promoters. Many of the drug-resistant organisms that humans get are ultimately derived from drug-resistant strains in animal reservoirs."

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"We need to be more selective about our use of antibiotics, not only in humans but also in animal feed," says Riley.

E. coli generally isn't thought of as causing outbreaks of urinary tract infections, but there are precedents, says the report. In London in 1987 and 1988, a strain caused an outbreak of cystitis, a bladder infection, and other diseases, and E. coli is an endemic cause of urinary tract infections in Barcelona, Spain.

Information about bacterial resistance to antibiotics is available from the Centers for Disease Control and Prevention and the Food and Drug Administration.

SOURCES: Interviews with Lee W. Riley, M.D., professor of epidemiology and public health, University of California at Berkeley, and Walter E. Stamm, professor of medicine, University of Washington, Seattle; Oct. 4, 2001, The New England Journal of Medicine
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