Table 4. Results, by study site, for select phenotype-based definitions used to identify carbapenemase producers among 307 carbapenem-resistant enterobacterial isolates from 4 US EIP, Emerging Infections Program sites, January 1, 2011–January 30, 2014*.

Site	No. isolates/no. tested (%), by definition no.†
	2‡			4§			5¶			4 plus MHT#
	FP	sFN		FP	sFN		FP	sFN		FP	sFN
Minnesota	51/111 (45.9)	3/111 (2.7)		55/111 (49.5)	1/111 (0.9)		25/111 (22.5)	5/111 (4.5)		23/111 (20.7)	1/111 (0.9)
Tennessee	17/65 (26.2)	4/65 (6.2)		50/65 (76.9)	1/65 (1.5)		18/65 (27.7)	4/65 (6.2)		3/65 (4.6)	1/65 (1.5)
Maryland	6/59 (10.2)	5/59 (8.5)		16/59 (27.1)	0/59		3/59 (5.1)	6/59 (10.2)		3/59 (5.1)	0/59
New York	4/53 (7.5)	2/53 (3.8)		31/53 (58.5)	0/53		8/53 (15.1)	1/53 (1.9)		3/53 (5.7)	0/53

*FP, false positive; MHT, the modified Hodge test; sFN, selected false negative.
†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).