This post has been updated.
A particularly dangerous superbug, dubbed the "phantom menace" by scientists, is on the rise in the United States, according to a report Thursday by the Centers for Disease Control and Prevention.
This superbug's strains belong to the family of bacteria known as CRE, which are difficult to treat because they are often resistant to most antibiotics. They are often deadly, too, in some instances killing up to 50 percent of patients who become infected, according to the CDC. Health officials have called CRE among the country's most urgent public health threats.
The target of Thursday's report is relatively new. Unlike more common types of CRE, it carries a plasmid, or mobile piece of DNA, with an enzyme that breaks down antibiotics. And what makes these bacteria even more dangerous is their ability to transfer that plasmid--and that antibiotic resistance--to normal bacteria that are present in our bodies.
This type of CRE has had a lower profile because it's actually less antibiotic-resistant than other more common types of CRE. As a result, it hasn't been a frequent focus of testing and has largely escaped detection by health officials, prompting some researchers to dub it "the phantom menace."
"This is a tricky drug-resistant bacteria, and it isn't easily found," CDC Director Thomas Frieden said in an interview. "What we're seeing is an assault by the microbes on the last bastion of antibiotics."
Bacteria develop antibiotic resistance in two ways.
Many can evolve their own genome in ways that deactivate antibiotics, although that ability can't be shared with pathogens outside their own family.
Yet other bacteria rely on a shortcut: They get infected with a plasmid carrying the resistance gene. That makes them more dangerous because plasmids can make copies of themselves and transfer within a family of bugs and as well as jump to other families of bacteria, which can then "catch" the resistance directly without having to develop it through evolution.
In a related alarming development, Danish researchers announced Thursday that a dangerous new superbug gene discovered in China two weeks ago had been found in bacteria infecting one person in Denmark. The gene makes the bacteria resistant to colistin, the antibiotic of last resort. And similar to the 'phantom menace' type of CRE, the gene is contained in a plasmid.
Experts warned that the latest development was frightening. "History shows that these mobile resistance genes can spread around the world quickly, silently riding in people, animals and food," said Lance Price, director of the Antibiotic Resistance Action Center at George Washington University's Milken Institute of Public Health, in a statement.
He said the news that the superbug gene first found in China has now turned up in Denmark "suggests that this scenario is playing out in real time," he said.
CDC received reports counting at least 43 patients in 19 states with this type of CRE superbug between June 2010 and August 2015. All cases were confirmed by CDC. Although the numbers are relatively small, Frieden said they are "just the tip of the iceberg." There was one patient with this type of superbug in 2010 and 11 patients each year in 2013, 2014 and 2015.
Most U.S. clinical laboratories that test for CRE organisms wouldn't identify this particular type of bacteria because it's not part of standard testing. CDC changed its definition of the organism in January to help increase detection.
CRE stands for carbapenem-resistant Enterobacteriaceae.