Table 5. Results, by organism tested, for select phenotype-based definitions used to identify carbapenemase producers among 307 carbapenem-resistant enterobacterial isolates from 6 US Emerging Infections Program sites, January 1, 2011–January 30, 2014*.
| Organism | Definition no., result, no. isolates/no. total (%)† |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| 2‡ |
4§ |
5¶ |
4 plus MHT# |
||||||||
| False-positive | Selected false-negative | False-positive | Selected false-negative | False-positive | Selected false-negative | False-positive | Selected false-negative | ||||
| Klebsiella spp. | 15/111 (13.5) | 14/111 (12.6) | 31/111 (27.9) | 1/111 (0.9) | 11/111 (9.9) | 14/111 (12.6) | 3/111 (2.7) | 1/111 (0.9) | |||
| Enterobacter spp. | 42/102 (41.2) | 0/102 | 68/102 (66.7) | 0/102 | 26/102 (25.5) | 0/102 | 30/102 (29.4) | 0/102 | |||
| Escherichia coli | 25/94 (26.6) | 1/94 (1.1) | 70/94 (74.5) | 1/94 (1.1) | 20/94 (21.3) | 3/94 (3.2) | 3/94 (3.2) | 1/94 (1.1) | |||
*MHT, the modified Hodge test. †False-positive isolates are those meeting the definition but not found to produce a carbapenemase. Selected false-negative isolates were selected on the basis of nonsuceptibility to >1 carbapenem not meeting the definition but found to produce a carbapenemase. ‡Definition 2 nonsusceptible to any carbapenem, excluding ertapenem, and resistant to all third-generation cephalosporins tested (pre-2015 Centers for Disease Control and Prevention carbapenem-resistant Enterobacteriaceae surveillance definition). §Definition 4, resistant to any carbapenem. This definition obtained the lowest number of selected false-negatives. ¶Definition 5, resistant to any carbapenem, excluding ertapenem. This definition obtained the lowest number of false-positives among definitions with selected false-negatives of <10%. #Definition 4 (resistant to any carbapenem) plus MHT (i.e., 2-step testing).