TABLE 3.
Performance of the CzIE rapid test according to β-lactamase type and high inoculum MIC
| BlaZ type (no. of isolates) | Cz MIC at HId (no. of isolates) | Rapid test result | CzIE detected by broth microdilution gold standardd |
% sensitivity (95% CI)d | % specificity (95% CI)d | |
|---|---|---|---|---|---|---|
| No. isolates with CzIE present (%) | No. isolates with CzIE absent (%) | |||||
| Type A (n = 186) | ≥32 μg/ml (n = 113) | Positive | 111 (98) | 0 | 98.2 (93.8–99.8) | NAa |
| Negative | 2 (2) | 0 | ||||
| Total | 113 | 0 | ||||
| 16 μg/ml (n = 24) | Positive | 16 (67) | 0 | 66.7 (44.7–84.4) | NAa | |
| Negative | 8 (33) | 0 | ||||
| Total | 24 | 0 | ||||
| ≤8 μg/ml (n = 49) | Positive | 0 | 6 (12) | NAc | 87.8 (75.2–95.4) | |
| Negative | 0 | 43 (88) | ||||
| Total | 0 | 49 | ||||
| Type B (n = 157) | ≥32 μg/ml (n = 12) | Positive | 6 | 0 | 50.0 (21.1–78.9) | NAa |
| Negative | 6 | 0 | ||||
| Total | 12 | 0 | ||||
| 16 μg/ml (n = 3) | Positive | 2 | 0 | 66.67 (NAb) | NAa | |
| Negative | 1 | 0 | ||||
| Total | 3 | 0 | ||||
| ≤8 μg/ml (n = 142) | Positive | 0 | 24 | NAc | 83.10 (75.9–88.7) | |
| Negative | 0 | 118 | ||||
| Total | 0 | 142 | ||||
| Type C (n = 205) | ≥32 μg/ml (n = 56) | Positive | 42 (75) | 0 | 75.0 (61.6–85.6) | NAa |
| Negative | 14 (25) | 0 | ||||
| Total | 56 | 0 | ||||
| 16 μg/ml (n = 45) | Positive | 31 (69) | 0 | 68.9 (53.4–81.8) | NAa | |
| Negative | 14 (31) | 0 | ||||
| Total | 45 | 0 | ||||
| ≤8 μg/ml (n = 104) | Positive | 0 | 18 (17) | NAc | 82.7 (74.0–89.4) | |
| Negative | 0 | 86 (83) | ||||
| Total | 0 | 104 | ||||
Not applicable due to inability to estimate the value. To calculate the specificity, the number of false positives (FP) and number of true negatives (TN) derived from the column that indicates “absence of the CzIE” are required. Therefore, we were unable to estimate this value since FP = 0 and TN = 0.
Not applicable due to small sample size.
Not applicable due to the inability to estimate the value. To calculate the sensitivity, the number of true positive (TP) and number of false negative (FN) derived from the column that indicates “presence of the CzIE” are required. Therefore, in these cases we were unable to estimate this value since TP = 0 and FN = 0.
CzIE, cefazolin inoculum effect, identified by broth microdilution at high inocula (107 CFU/ml); CI, confidence interval; HI, high inoculum.