Table 3. False-positive and selected false-negative results in a study evaluating phenotype-based definitions for reliability in identifying carbapenemase producers among carbapenem-resistant enterobacterial isolates from 6 US Emerging Infections Program sites, January 1, 2011–January 30, 2014.

Result	No. isolates/no. tested (%), by definition no., N = 307*
	1	2	3	4	5	6	7	8	9	10	11
False-positive	117/307 (38.1)	82/307 (26.7)	91/307 (29.6)	169/307 (55.0)	57/307 (18.6)	146/307 (47.6)	153/307 (49.8)	60/307 (19.5)	37/307 (12.1)	34/307 (11.1)	17/307 (5.5)
Selected false-negative	12/307 (3.9)	15/307 (4.9)	13/307 (4.2)	2/307 (0.7)	17/307 (5.5)	7/307 (2.3)	4/307 (1.3)	27/307 (8.8)	85/307 (27.7)	85/307 (27.7)	85/307 (27.7)

*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. Definitions: 1, nonsusceptible to any carbapenem, excluding ertapenem; 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); 3, nonsusceptible to any carbapenem, excluding ertapenem, and resistant to any third-generation cephalosporins tested; 4, resistant to any carbapenem; 5, resistant to any carbapenem, excluding ertapenem; 6, resistant to any carbapenem and resistant to all third-generation cephalosporins tested; 7, resistant to any carbapenem and resistant to any third-generation cephalosporin tested; 8, nonsusceptible to at least 2 carbapenems (ertapenem resistant, if tested); 9, nonsusceptible to any carbapenem (ertapenem resistant, if tested) and resistant to cefepime; 10, resistant to any carbapenem and resistant to cefepime; and 11, nonsusceptible to any carbapenem, excluding ertapenem, and resistant to cefepime.