Eight patients in a Denver hospital last year harbored Klebsiella pneumoniae carrying New Delhi metallo-beta-lactamase (NDM), an enzyme that confers resistance to many antimicrobials, marking the biggest such outbreak in the United States so far, according to the Centers for Disease Control and Prevention (CDC).
The outbreak was first spotted with the detection of carbapenem-resistant K pneumoniae (CRKP) in respiratory samples from two patients in July and August, says an article in today's Morbidity and Mortality Weekly Report (MMWR). Review of records and surveillance cultures identified six more cases.
The patients had been hospitalized for a median of 18 days before CRKP was identified. Three of them were treated for CRKP infections, and five were found to be asymptomatically colonized. All of them survived. Tests revealed that the initial isolates were resistant to all antimicrobials except tigecycline.
An epidemiologic investigation suggested that multiple transmission events had occurred and that "undetected, asymptomatically colonized patients were involved in some transmission routes."
How the pathogen got into the hospital was unclear. Before this outbreak, only 16 isolates of NDM-producing carbapenem-resistant Enterobacteriaceae (CRE) had been found in the United States, 14 of them in patients who had received medical care in South Asia.
In a Health Alert Network advisory e-mailed to reporters today, the CDC said that, of the 37 unusual forms of CRE reported in the United States, 15 have been reported since July 2012. The agency called for healthcare providers to act aggressively to prevent the emergence and spread of these organisms.