While the discovery of this superbug in two pig samples is alarming, there’s more. A Pennsylvania woman--who reportedly has not traveled outside the U.S. recently--tested positive for the same E. coli strain--the first human case of the colistin-resistant strain detected in the U.S. That patient has since been treated and her urine shows no more signs of the bacteria.

Health officials had been tracking outbreaks in Asia, Canada and Europe. Between the human case and the two pig samples, it’s clear that the superbug--known as the mcr-1 gene--has made its way into the U.S. It had already been detected--among pigs and humans--in China as of late 2015. It appears to be far more common among animals than humans.

The Washington Post states, “Public health officials' biggest fear is that the gene will spread to bacteria that are now susceptible only to colistin. In all three cases here, the gene was carried on a plasmid, a mobile piece of DNA that easily can transfer the gene to other bacteria. That would result in a kind of super-superbug, invincible to every life-saving antibiotic available.”

USDA has not revealed the fate of either pig used for these sample tests. Both pigs were from U.S. slaughterhouses. The second pig sample is still being further analyzed.

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