Along with becoming more resistant to antibiotics, the “H30-Rx” strain developed the unprecedented ability to spread from the urinary tract to the bloodstream and cause an extremely dangerous infection called sepsis.

This means that the H30-Rx stain poses a threat to the more than 10 million Americans who develop a urinary tract infection each year, according to the study authors.

They said this strain of appears to be much more able than other E. coli strains to move from the bladder to the kidneys and then into the bloodstream. H30-Rx may be responsible for 1.5 million urinary tract infections and tens of thousands of deaths each year in the United States, according to the study published Dec. 17 in the journal MBio.

Genetic analyses revealed how H30-Rx came into being. More than two decades ago, a strain called H30 developed mutations in two genes. This resulted in a clone called H30-R, which was resistant to the antibiotic Cipro. Soon after, H30-R gave rise to H30-Rx, which is resistant to several antibiotics.

By focusing on H30-Rx, it might be possible to develop a vaccine that could prevent many infections, according to the study authors.

“This strain of E. coli spreads from person to person, and seems to be particularly virulent,” study co-author James Johnson, of the Veterans Affairs Medical Center and the University of Minnesota, said in a journal news release.

“This study might help us develop better tools to identify, stop or prevent its spread by finding better ways to block the transmission of the superbug, or by finding a diagnostic test that would help doctors identify such an infection early on — before it might have the chance to turn lethal,” he explained.

“We now know that we are dealing with a single enemy, and that by focusing on this strain we can have a substantial impact on this worldwide epidemic,” study co-author Evgeni Sokurenko, of the University of Washington School of Medicine, said in the news release.