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Table 2 Sensitivity (Se, %), specificity (Sp, %), positive and negative likelihood ratios (LR+ and LR-, respectively) of screening strategies for carbapenemase-positive isolates among 349 isolates non-susceptible to ertapenem

From: Development of an algorithm for phenotypic screening of carbapenemase-producing Enterobacteriaceae in the routine laboratory

Antibiotic and diameter (< in mm) Number (%) of isolates Se
%
Sp
%
LR+ LR-
Carbase+
(n = 52)
Carbase-
(n = 297)
Clinical breakpoints
 IMI 24 22 (42.3) 44 (14.8) 42.3 85.2 2.84 0.68
 MER 22 22 (42.3) 40 (13.5) 42.3 86.5 3.12 0.67
 DOR 24 17 (32.7) 22 (7.4) 32.7 92.6 4.37 0.72
 TAZ 21 51 (98.1) 220 (74.1) 98.1 25.9 1.31 0.11
 TCC 24 51 (98.1) 292 (98.3) 98.1 1.7 0.99 1.53
 FEP 24 42 (80.8) 138 (46.5) 80.8 53.5 1.73 0.37
Cut-offs
 MER 27 a 40 (76.9) 80 (27.0) 76.9 73.0 2.83 0.32
 TEM 8 a 35 (67.3) 12 (4.0) 67.3 96.0 15.97 0.34
 TAZ 16 b 46 (88.5) 105 (35.4) 88.5 64.7 2.48 0.19
 TEM 12 b 43 (82.7) 65 (21.9) 82.7 78.1 3.73 0.23
 MER 25 c 32 (61.5) 59 (19.9) 61.5 80.1 3.07 0.48
 TCC 15 d 51 (98.1) 227 (76.4) 98.1 23.6 1.27 0.12
 TEM 15 d 50 (96.2) 126 (42.4) 96.2 57.6 2.24 0.08
 FEP 26 d 43 (82.7) 162 (54.6) 82.7 45.4 1.51 0.39
Combination of cut-offs
 TAZ 16 & TEM 12 b* 39 (75.0) 48 (16.2) 75.0 58.9 4.62 0.08
 TCC 15 & TEM 15 d 50 (96.2) 94 (31.7) 96.2 68.3 3.00 0.07
 TCC 15 & TEM 15 & IMI 22 d 52 (100) 109 (36.7) 100 63.3 2.70 0.01
 TCC 15 & TEM 15 & MER 22 d 52 (100) 110 (37.0) 100 63.0 2.67 0.01
 TCC 15 & TEM 15 & IMI 22 & FEP 26 d 52 (100) 92 (31.0) 100 69.0 3.19 0.01
 TCC 15 & TEM 15 & MER 22 & FEP 26 d 52 (100) 93 (31.3) 100 68.7 3.16 0.01
Combination of cut-offs + additional tests
 TCC 15 & TEM 15 & IMI 22 & IMI 32-Clo d,e 51 (98.1) 81 (27.3) 98.1 72.7 3.55 0.04
 TCC 15 & TEM 15 & MER 22 & MER 32-Clo d,e 52 (100) 68 (22.9) 100 77.1 4.31 0.01
 TCC 15 & TEM 15 & IMI 22 & FEP 26 d & IMI 32-Clo d,e 51 (98.1) 71 (23.9) 98.1 76.1 4.05 0.04
 TCC 15 & TEM 15 & MER 22 & FEP 26d & MER 32-Clod,e 52 (100) 63 (21.2) 100 78.8 4.65 0.01
 MER 25 & TEM 11 & Rosco confirm kit c,f 29 (55.8) 23 (9.4) 55.8 90.6 5.82 0.49
 MER 27 & TEM 8 & Rosco confirm kit a,g 36 (69.2) 14 (4.7) 69.2 95.3 14.15 0.33
  1. IMI imipenem, MER meropenem, DOR doripenem, FEP cefepime, TAZ piperacillin/tazobactam, TCC ticarcillin/clavulanate, TEM temocillin, Carbase+ or Carbase- carbapenemase-positive or -negative isolate
  2. areference [13]; b*85 (24.4%) isolates not classified according to reference [14] strategy; creference [15]; dthis study
  3. ecloxacillin test applied only to chromosomally encoding AmpC Enterobacteriaceae
  4. f258 (73.9) of our isolates not tested according to reference [15] because of meropenem diameter ≥25 mm towards these isolates
  5. g 229 (65.6%) of our isolates not tested according to reference [13] because of meropenem diameter ≥27 mm towards these isolates