Three people returned to the US from India earlier this year infected with the newly described "superbugs" that are highly resistant to antibiotics, according to media reports.
All three confirmed cases - one each in California, Illinois and Massachusetts - involved people who got medical care in India, the Chicago Tribune said citing the US Centres for Disease Control and Prevention (CDC).
The Illinois patient recovered, and there is no evidence the infection was transmitted to other people, the daily said citing Illinois Department of Public Health spokeswoman Melaney Arnold who released no other details about the case.
Another person was treated at Massachusetts General Hospital and isolated, a measure that prevented the germ from spreading, said David Hooper, chief of the hospital's infection control unit, the Boston Herald said.
The Massachusetts patient too survived. The daily said the superbug seems to have been contained.
All three patients developed urinary tract infections that carried a genetic feature that made their cases harder to treat.
Known as NDM-1 - short for New Delhi metallo-beta-lactamase - the gene allows bacteria to escape some of the strongest antibiotics available, a process known as drug resistance.
"All three of the US patients had been in India, and two - including the person treated at Massachusetts General - underwent medical procedures in hospitals while they were there," Medical epidemiologist Alex Kallen of CDC said
The patient treated in Boston was an Indian citizen with cancer who had undergone surgery and chemotherapy in that country before coming to Massachusetts, he said.
Kallen warned against panic. Although the NDM-1 mechanism is new, he said, other bacteria already found in the state also can evade carbapenems.
"That is not to downplay this," he said. "It is important, but this particular mechanism is just one of many that can cause this kind of pattern."