Carbapenemase-producing Klebsiella pneumoniae and Hematologic Malignancies

To the Editor: Until a few years ago, the most frequent microbiologi-cally documented cause of severe bloodstream infections among patients with hematologic malignancies was gram-positive bacteria (1). However , over the years, gram-negative bacteria have become the main infectious cause of death among patients with hematologic malignancies, and rates of different phenotypes associated with antimicrobial drug resistance are increasing (2). This trend could be the result of increasing empirical use of antimicrobial drug therapy and pro-phylaxis and use of new, more effective antimicrobial drugs. In particular, over the past few years at our hospital (Agostino Gemelli Teaching Hospital , Rome, Italy), we have observed a progressive increase in bloodstream infections caused by Klebsiella pneu-moniae carbapenemase–producing K. pneumoniae (KPC-Kp), which are responsible for a dramatic new scenario. We reviewed records of all patients affected by hematologic malignancies who were admitted to the hospital hema-tology department from January 2009 through December 2012 and in whom a bloodstream infection caused by gram-negative bacteria developed. A KPC-Kp bloodstream infection was defined as a bloodstream infection documented on the basis of blood culture positivity (at least 1 specimen) for a KPC-Kp strain and clinical signs of systemic inflam-matory response syndrome. The Vitek 2 system (bioMérieux. Firenze, Italy) was used for isolate identification and antimicrobial drug susceptibility testing ; PCR and sequencing, as previously described, was used to identify bla KPC genes (3). Antibiograms were reported 72–120 hours (median 76 hours) after onset of bloodstream infection. Death was considered attributable to infection for patients who died within 2 weeks after the first positive blood culture and for whom other potential causes of death could be excluded. During the study period, we detected 147 bloodstream infections caused by gram-negative bacteria, 38 (25%) of which were caused by K. pneumoni-ae; of these, 26 (18%) were caused by KPC-Kp. We did not identify any episodes of recurrent KPC-Kp bloodstream infection. We did document a progressive , exponential increase in infections caused by KPC-Kp. No KPC-Kp cases were documented until 2009, and cases increased from only 1 case in 2010 to 12 cases in 2012 (Table). The incidence of KPC-Kp among all gram-negative causes of bloodstream infections in-9 neutrophils/ mL for >10 days); almost half (12/26, 46.1%) of these patients experienced complete remission during the course of consolidation therapy or were receiving initial chemotherapy. Among KPC-Kp isolates, 80.8% were susceptible to co-listin, 69.2% to tigecycline, and 65.4% to gentamicin. The …