Doctors have discovered a new bacterial strain that accounts for a striking portion of drug-resistant urinary tract infections among women. The bug's prevalence over a wide geographic area cannot be accounted for by its usually sluggish mode of transmission.
Urinary tract infections affect 11% of U.S. women each year. Because they typically spread from person to person through the ingestion of fecal material, epidemics in which the same strain spreads over a large area are rare. Most urinary tract infections are easily cured with standard antibiotics, but in some parts of the country as many as 20% only respond to a combination of powerful drugs.
To study the epidemiology of the disease, Lee Riley and his colleagues at the University of California, Berkeley, examined bacteria in urine samples of 228 women who sought treatment at Berkeley's health center. To their surprise, they found that a single, previously unknown Escherichia coli strain accounted for more than half of the 55 drug-resistant infections. A follow-up study found that the same strain, dubbed "clonal group A," also caused about 40% of resistant infections in two smaller study sites in Ann Arbor, Michigan, and Minneapolis, Minnesota.
Such simultaneous outbreaks are common for E. coli strains that cause food poisoning, but are hard to explain through the fecal transmission route, Riley and his team write in the 4 October issue of The New England Journal of Medicine. The researchers theorize that the bacteria in each of the three locations share a common recent origin.
Such a scenario is possible and contaminated food may be the culprit, says Walter Stamm, an infectious disease expert at the University of Washington in Seattle. But he cautions that further study is needed to determine whether this strain poses a major risk to public health.