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For the first time, doctors have diagnosed a patient in the U.S. with a superbug resistant to the so-called antibiotic of last resort, the Washington Post reported on Thursday.

The strain of E. coli was found in the urine of a 49-year-old Pennsylvania woman last month, who went to the doctor with symptoms common for a urinary tract infection, according to a report published in the Antimicrobial Agents and Chemotherapy journal.

With most antibiotic-resistant superbugs, doctors have been able to rely on colistin, an antibiotic of last resort that can kill the dangerous bacteria.

The strain found in the woman’s urine is resistant to colistin, according to the authors of the report, who wrote the discovery, “heralds the emergence of a truly pan-drug resistant bacteria.”

Centers for Disease Control and Prevention Director Dr. Thomas Frieden speaks in 2015 about the fight against antibiotic-resistant strains:

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Medical professionals have long warned the evolution of antibiotic-resistant strains could lead to an unparalleled medical crisis, with minor infections or simple surgeries becoming fatal.

“It basically shows us that the end of the road isn’t very far away for antibiotics — that we may be in a situation where we have patients in our intensive-care units, or patients getting urinary tract infections for which we do not have antibiotics,” CDC director Tom Frieden told the Post. “I’ve been there for TB patients. I’ve cared for patients for whom there are no drugs left. It is a feeling of such horror and helplessness.”

The deadly superbug made news in November 2015 after researchers from China and the UK found the bacteria in a small group of people in China, as well as in pigs and raw pork meat. The colistin-resistant superbug has also been found in Europe and Africa.