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Comparative risk factors for nosocomial New Delhi metallo-beta-lactamase (NDM-1) producing Enterobacteriaceae and non-carbapenemase producing (NCP) Enterobacteriaceae

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Carbapenem resistance occurs via two mechanisms: acquisition of resistance genes (NDM-1, KPC, OXA) or combination of extended spectrum beta-lactamase production and alteration of the expression of porins (NCP Enterobacteriaceae).


We conducted a case-case-control study to identify if NDM-1 Enterobacteriaceae share risk factors with NCP Enterobacteriaceae.


Patients admitted for at least 48 hours between September 2010 and July 2013 were included. Case 1: Patients with NDM-1 Enterobacteriaceae isolated from either clinical or surveillance cultures. Case 2: Patients with NCP Enterobacteriaceae isolated from either clinical or surveillance cultures. Control: Patients screened negative for carbapenem-resistant Enterobacteriaceae (CRE). Patients with both NDM-1 Enterobacteriaceae and NCP Enterobacteriaceae were excluded. Demographic, clinical, microbiological and antibiotics usage data were collected from electronic medical records. We conducted time at risk adjusted bivariate analysis followed by multivariate analysis using STATA 12.0.


A total of 1934 patients were screened for CRE. A total of 40 NDM-1 Enterobacteriaceae and 43 NCP Enterobacteriaceae patients were compared with 61 randomly selected control patients. There was no significant difference in age, sex and Charlson index between cases and controls. Independent risk factor for NDM-1 Enterobacteriaceae was intensive care unit (ICU) admission in the preceding 3 months (OR, 3.2; 95% CI 1.2 – 8.6; p=0.02) and for NCP Enterobacteriaceae was number of days exposed to carbapenems (OR 1.2; 95% CI 1.1 – 1.3; p=0.002).


NDM-1 Enterobacteriaceae and NCP Enterobacteriaceae do not share similar risk factors in this small single center study. This finding has an implication on infection control strategies for CRE control.

Disclosure of interest

None declared.

Author information

Correspondence to E Izharuddin.

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  • Electronic Medical Record
  • Carbapenems
  • Share Risk
  • Charlson Index
  • Antibiotic Usage