Carbapenem resistance among Klebsiella pneumoniae isolates: risk factors, molecular characteristics, and susceptibility patterns.

BACKGROUND: Carbapenem resistance among isolates of Klebsiella pneumoniae has been unusual.

OBJECTIVES: To identify risk factors for infection with carbapenem-resistant K. pneumoniae (CRKP) and to characterize microbiological aspects of isolates associated with these infections.

DESIGN: Retrospective case-control study.

SETTING: A 900-bed tertiary care hospital.

RESULTS: From January 2006 through April 2007, K. pneumoniae was isolated from 461 inpatients; 88 had CRKP infection (case patients), whereas 373 had carbapenem-susceptible K. pneumoniae infection (control subjects). The independent risk factors for infection with CRKP were prior fluoroquinolone use (odds ratio [OR], 1.87 [95% confidence interval [CI], 1.07-3.26]; P=.026), previous receipt of a carbapenem drug (OR, 1.83 [95% CI, 1.02-3.27]; P=.042), admission to the intensive care unit (OR, 4.27 [95% CI, 2.49-7.31]; P<.001), and exposure to at least 1 antibiotic drug before isolation of K. pneumoniae (OR, 3.93 [95% CI, 1.15-13.47]; P=.029). All CRKP isolates carried the bla(KPC) gene. Approximately 90% of the tested isolates carried the bla(KPC-2) allele, suggesting patient-to-patient transmission. Almost all CRKP isolates were resistant to all antibiotics, except to colistin (resistance rate, 4.5%), gentamicin (resistance rate, 7%), and tigecycline (resistance rate, 15%).

CONCLUSIONS: CRKP should be regarded as an emerging clinical threat. Because these isolates are resistant to virtually all commonly used antibiotics, control of their spread is crucial.