Outbreak of Colistin-Resistant, Carbapenem-ResistantKlebsiella pneumoniaein Metropolitan Detroit, Michigan

Abstract

ABSTRACTCarbapenem-resistantKlebsiella pneumoniaehas spread worldwide and throughout the United States. Colistin is used extensively to treat infections with this organism. We describe a cluster of colistin-resistant, carbapenem-resistantK. pneumoniaeinfection cases involving three institutions in Detroit, MI. A cluster of five cases of colistin-resistant, carbapenem-resistantK. pneumoniaewas identified at Detroit Medical Center (DMC) from 27 July to 22 August 2009. Epidemiologic data were collected, and transmission opportunities were analyzed. Isolates were genotyped by using pulsed-field gel electrophoresis and repetitive extragenic palindromic PCR. Data regarding the use of colistin were obtained from pharmacy records. The index case of colistin-resistant, carbapenem-resistantK. pneumoniaewas followed 20 days later by four additional cases occurring in a 6-day interval. All of the patients, at some point, had stayed at one particular institution. The mean number of opportunities for transmission between patients was 2.3 ± 0.5, and each patient had at least one opportunity for transmission with one of the other patients. Compared to 60 colistin-susceptible, carbapenem-resistantK. pneumoniaecontrols isolated in the previous year at DMC, case patients were significantly older (P= 0.05) and the carbapenem-resistantK. pneumoniaeorganisms isolated from them displayed much higher MICs to imipenem (P< 0.001). Colistin use was not enhanced in the months preceding the outbreak. Genotyping revealed two closely related clones. This report of a colistin-resistant, carbapenem-resistantK. pneumoniaeoutbreak is strongly linked to patient-to-patient transmission. Controlling the spread and novel emergence of bacteria with this phenotype is of paramount importance.