The “new superbug” MCR—actually a gene, carried by gut bacteria, that confers resistance to the absolutely last-ditch antibiotic colistin—has been in the United States for at least a year, according to a new report.

The gene was first identified last year and caused a flurry of alarm when it was spotted for the first time in the U.S. in May, after being found in bacteria from people, animals and meat in more than 30 countries.

That first U.S. identification came from a just-diagnosed woman in Pennsylvania. But in a letter posted Monday by the journal Antimicrobial Agents and Chemotherapy, researchers from JMI Laboratories in Iowa say they have found a second instance of MCR that is more than a year old. It was found in a stored sample of E. coli that was collected in May 2015 in New York.

The new discovery confirms that the Pennsylvania case was not the first MCR-related infection in the U.S., but only the first to be found—making it a reasonable assumption that there are others that have not been identified yet.

Also, in both patients the bacteria harboring the gene were susceptible to other antibiotics—which raises the possibility that this new resistance factor may be less of an immediate health threat, and more like a time bomb with an unpredictably long fuse.

But along with new European research announced last week and a troubling new finding reported today, the U.S. discovery reinforces that for medicine and public health to protect the population from that time bomb going off—that is, from the arrival of completely untreatable infections—they will need to start doing a lot more looking for MCR than they do now.