Asymptomatic carriage of carbapenem-resistant Enterobacteriaceae is “considerable,” according to genetic analyses of bacterial isolates obtained from patients at four large U.S. hospitals.

To better understand the “urgent threat” of carbapenem resistance – specifically, to obtain a “snapshot” of how the resistant enterobacteria evolve, diversify, and spread – the researchers performed genetic analyses on 122 carbapenem-resistant and 141 carbapenem-susceptible bacterial isolates from patients hospitalized during a 16-month period at three Boston and one California medical centers. The isolates were obtained from urine (44%), respiratory tract (16%), blood (11%), wound (11%), and other samples, said Gustavo C. Cerqueira, PhD, of the Broad Institute of MIT and Harvard University in Cambridge, Mass., and his associates.

They found 8 species of bacteria that exhibited carbapenem resistance, chiefly Klebsiella pneumoniae. There also was a significant degree of diversity among resistant Enterobacteria. Most importantly, the investigators found evidence of substantial asymptomatic carriage of resistant bacteria and discovered several previously unrecognized mechanisms that produced resistance. Taken together, the findings indicate “continued innovation by these organisms to thwart the action of this important class of antibiotics,” reported Dr. Cerqueira, also affiliated with Massachusetts General Hospital in Boston, and his associates (Proc Nat Acad Sci USA. 2017 Jan 16 [ doi:10.1073/pnas.1616248114 ]).

The study findings underscore the need for “an aggressive approach to surveillance and isolation” to control this continuing threat, they added.

This work was supported by the National Institute of Allergy and Infectious Diseases. Dr. Cerqueira and his associates reported having no relevant financial disclosures.