Carbapenem antibiotics are used to treat serious infections caused by extended-spectrum β-lactamase–carrying pathogens. Carbapenem resistance has been unusual in isolates of Klebsiella pneumoniae. In this study, the prevalence and molecular epidemiologic characteristics of carbapenem-resistant K pneumoniae are analyzed, and the experience involving 2 hospital outbreaks is described.
A citywide surveillance study was conducted in hospitals in Brooklyn. An observational study involving subsequent outbreaks at 2 hospitals was undertaken. Isolates were genetically fingerprinted by ribotyping and were examined for the presence of KPC-type carbapenem-hydrolyzing β-lactamases.
Of 602 isolates of K pneumoniae collected during the citywide surveillance study, 45% had extended-spectrum β-lactamases. Of the extended-spectrum β-lactamase–producing isolates, 3.3% carried the carbapenem-hydrolyzing β-lactamase KPC-2. Several isolates were reported by the clinical microbiology laboratories as being susceptible to imipenem. Although all the isolates were resistant using agar diffusion methods, minimal inhibitory concentrations of imipenem were substantially lower for several isolates using standard broth microdilution tests and were highly dependent on the inoculum used. Two hospitals experienced the rapid spread of carbapenem-resistant isolates involving 58 patients. Overall 14-day mortality for bacteremic patients was 47%. Most isolates belonged to a single ribotype.
Carbapenem-resistant K pneumoniae isolates are rapidly emerging in New York City. The spread of a strain that possesses a carbapenem-hydrolyzing β-lactamase has occurred in regional hospitals. Because these isolates are resistant to virtually all commonly used antibiotics, control of their spread is crucial. However, automated systems used for susceptibility testing may not accurately identify all these isolates, which will severely hamper control efforts.