BACKGROUND: Carbapenem-resistant Enterobacteriaceae (CRE) are an emerging threat. Carbapenemase-producing CRE (CP-CRE) are associated with widespread antibiotic resistance and dissemination in health care facilities. To prevent spread of CP- and non-CP-CRE in facilities, hospitalized patients are placed in enhanced precautions. To better capture CP-CRE incidence, the Council of State and Territorial Epidemiologists (CSTE) CRE definition was changed in 2016 from “non-susceptible to a carbapenem (excluding ertapenem) and resistant to all third generation cephalosporins tested,” to “resistance to any carbapenem (including ertapenem)" using current Clinical and Laboratory Standards Institute interpretive criteria. Prior definitions excluded ertapenem based on elevated MICs to this antibiotic caused by non-carbapenemase-mediated resistance mechanisms (e.g. AmpC beta-lactamase, porin loss), often seen in Enterobacter spp. We describe the impact of this definition change on CRE case volume and CP-CRE case identification.
METHODS: The Minnesota Department of Health (MDH) conducts active, laboratory-based surveillance for CRE in the two most populous counties, including isolate submission to the MDH-Public Health Laboratory (PHL) for carbapenemase testing. The 2015 and 2016 definitions were applied to Enterobacter spp., Klebsiella spp., and E. coli isolates submitted in 2016. The 2016 definition was also applied excluding ertapenem to determine the role of ertapenem alone in increase in CRE volume. Multiple isolates of the same organism from single patients were excluded.
RESULTS: In 2016, 319 isolates of Enterobacter spp., Klebsiella spp., and E. coli were submitted to MDH-PHL; 201 (63%) of these were Enterobacter spp. Overall, this is a 126% increase over submissions in 2015. Of isolates submitted in 2016, 85 (27%) met the 2015 CRE definition; 18 (21%) of these were CP-CRE (9 K. pneumoniae, 2 E. coli, 7 E. cloacae). In contrast, 281 (88%) isolates met the 2016 CRE definition; 21 (7%) were CP-CRE (11 K. pneumoniae, 3 E. coli, 7 E. cloacae). 3 CP-CRE that met the 2016 definition would have been missed using the 2015 definition (2 K. pneumoniae, 1 E. coli). Of the 281 isolates that met the 2016 definition, 190 (68%) were based on resistance to ertapenem alone; 135 (71%) of these were Enterobacter spp.
CONCLUSIONS: The 2016 definition change did identify additional CP-CRE in Klebsiella spp. and E. coli but resulted in submission of a high proportion of non-CP Enterobacter spp., the majority of which were resistant to ertapenem alone. A more specific definition for Enterobacter spp. could reduce CRE case volume without detriment to CP-CRE identification, reducing financial burden of implementing infection control measures.