E. coli bacteria strain found in country for the first time as experts warn more cases should be expected in the future.
A 49-year-old woman has become the first person in the US to be infected with a superbug, an alarming new development in the spread of bacteria that cannot be treated by any antibiotics.
US health officials said on Thursday a strain of E. coli bacteria resistant to colistin, which is known as a treatment of last resort, was found in a Pennsylvania woman who had visited a clinic with symptoms of a urinary tract infection.
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Colistin "was an old antibiotic, but it was the only one left for what I call nightmare bacteria", said Thomas Frieden, chief of the US Centers for Disease Control and Prevention.
The woman had not travelled outside the US, so could not have acquired the resistant bacteria elsewhere, Frieden added.
He said more cases should be expected in the future, raising concerns that the superbug could pose a serious danger for routine infections if it spreads.
"We know now that the more we look, the more we are going to find," he said. "We risk being in a post-antibiotic world."
Colistin has been available since 1959 to treat infections caused by E. coli, salmonella and acinetobacter, which can cause pneumonia or serious blood and wound infections.
It was abandoned for human use in the 1980s due to high kidney toxicity, but is widely used in livestock farming, especially in China.
However, colistin has been brought back as a treatment of last resort in hospitals and clinics as bacteria have started developing resistance to other, more modern drugs.
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The US has committed $1.2bn of its 2016 budget to tackling the issue, while the UK government has been providing financial incentives to get drug companies to boost research and production of new antibiotics.
Overprescribing of antibiotics by physicians and in hospitals and their extensive use in food livestock have been blamed for contributing to the crisis.
More than half of all patients treated in hospital will get an antibiotic at some point during their stay.
But studies have shown that 30 to 50 percent of antibiotics prescribed in hospitals are unnecessary or incorrect, contributing to antibiotic resistance.
In the US, antibiotic resistance has been blamed for at least two million illnesses and 23,000 deaths a year.