Making rounds in the United States is a particularly dangerous superbug – and it isn’t called the “phantom menace” for nothing, according to a new U.S. Centers for Disease Control and Prevention (CDC) report.

The strains of this superbug are part of a bacterial family called carbapenem-resistant Enterobacteriaceae (CRE), now considered an urgent public health concern and are highly tough to treat due to their antibiotic resistance. The CDC warned that they often lead to death in up to 50 percent of infection cases.

Published Dec. 3, the CDC report pointed to a relatively new target, which unlike typical CRE types, carried a plasmid – mobile DNA pieces – with an enzyme breaking down antibiotics.

The dangerous part: they can transfer that plasmid and antibiotic resistance to normal bacteria found in the body.

CDC Director Thomas Frieden dubbed it a tricky superbug, one not readily detected.

"What we're seeing is an assault by the microbes on the last bastion of antibiotics," he said in an interview.

This CRE type is known to be low-profile due to its less antibiotic-resistant quality than most other common types, allowing it to escape the probing eye of health officials.

Antibiotic resistance happens via two ways: some bacteria evolve their own genome such that antibiotics are deactivated, while others get infected with a plasmid that carries the resistance gene.

Based on reports received by CDC, at least 43 individuals in 19 states were struck with the CRE superbug from June 2010 to August 2015. While relatively small, the numbers tell the CDC that this is just the tip of the iceberg.

The health agency is also monitoring infections from other CRE types. There have been 118 cases, for instance, that involve a specific enzyme separate from the one detected in the bacteria which was the focus of the Thursday report.

Carbapenems are not the last line of defense against Enterobacteriaceae infections, but the growing resistance problem remains a cause for concern. Antibiotic resistance limits the number of drugs that can be used for treating bacterial conditions.

Danish researchers also declared that a sinister new superbug gene found in China two weeks earlier had also been found in bacteria that infected someone in Denmark. The gene mcr-1 makes bacteria resistant to colistin, the last-resort antibiotic.

Infection disease expert Dr. William Schaffner from Vanderbilt University Medical Center called for doctors and the public to work together and be more prudent in using antibiotics to combat the mounting resistance concern worldwide.

Photo: Oliver Dodd | Flickr