Carbapenem-resistant Enterobacteriaceae, or CRE, infects about 9,300 people, killing about 600 of them in the United States every year—and more people could be carrying the bacteria without knowing it.

Findings of a new study suggest that the bacteria may spread silently, infecting people without causing any symptoms.

CREs Spreading Stealthily

Researchers have been tracking the family of these superbugs that can resist antibiotics of last resort, but the study published in the Proceedings of the National Academy of Sciences on Jan. 16 hints there's much about this class of bacteria that researchers may not yet be aware of.

CREs appear to have more ways of evading antibiotics than what researchers have currently identified. The bacteria may also be spreading more stealthily than current surveillance can detect.

Study researcher William Hanage, from Harvard T. H. Chan School of Public Health, and colleagues collected and genetically sequenced more than 250 CRE isolates that were responsible for diseases in four U.S. hospitals over a 16-month period. The isolates were drawn from patients' blood, respiratory tract, urine samples, and wound.

Eight species of CRE were eventually found at the four hospitals. Researchers found a variety of CRE types within each hospital, and these bacteria span several species with a range of genetic backgrounds and resistance genes.

The numbers and the fact that few of the isolates seem to be genetically related surprised the researchers because these mean that drug-resistance spread faster and more easily between the strains than expected.

Spreading Without Causing Any Symptom

Some of the species did not carry the genes that are known to suppress carbapenems, the antibiotics used to treat infections believed to be caused by multidrug resistant bacteria, but they were able to survive carbapenems, which hint that these pathogens have managed to find a way to avoid these antibiotics that researchers are not yet aware of.

Hanage and colleagues did not also find a clear pattern of transmission for the CRE strains. The resistance appears to be spreading without obvious cases of illness or infection, which could mean transmission happen from one person to another asymptomatically.

"While the typical focus has been on treating sick patients with CRE-related infections, our new findings suggest that CRE is spreading beyond the obvious cases of disease. We need to look harder for this unobserved transmission within our communities and healthcare facilities if we want to stamp it out," Hanage said.

The findings suggest that CREs easily adapt, and the variety with which they appear in the sick may be explained by a possible silent transmission among the healthy. More surveillance that would involve both healthy and sick people to prove this speculation is needed, but if this turns out true, study researchers said it is crucial to reconsider the strategies being used to fight these microbes.

"We provide evidence for considerable asymptomatic carriage and unrecognizable mechanisms of carbapenem resistance that, together, indicate continued innovation by these organisms to thwart the action of this important class of antibiotics and underscore the need for continued surveillance of CRE," the researchers wrote in their study.

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