TABLE 3.
Diagnostic performance of the mCIM and eCIM with 0.1 and 5 mM EDTAa
| Test (no. of isolates) | % (95% CI) |
|
|---|---|---|
| Sensitivity | Specificity | |
| mCIM (75) | 100b (91.4–100) | 100 (89.7–100) |
| eCIM, 0.1 mM EDTA (40)c | 75d (50.9–91.3) | 100 (83.2–100) |
| eCIM, 5 mM EDTA (40)c | 100 (83.2–100) | 100e (83.2–100) |
CI, confidence interval; eCIM, EDTA-modified carbapenem inactivation method; mCIM, modified carbapenem inactivation method.
Initially, for the mCIM test, two non-carbapenemase-producing isolates, K. aerogenes (ARB0009) and K. pneumoniae (ARB0012), yielded indeterminate results. Upon repeat testing, the mCIM was negative.
One isolate, K. pneumoniae (ARB0153), harbored both NDM and OXA-48-type enzymes. This isolate was not included in the diagnostic performance evaluation of the eCIM. However, as expected, it tested positive for the mCIM, but negative for the eCIM with both 0.1 and 5 mM EDTA.
Five isolates tested falsely negative with the eCIM in the presence of 0.1 mM EDTA initially and upon repeat testing.
Two isolates, ARB0066 and ARB0075, both K. pneumoniae isolates encoding OXA-48-type (OXA-232) enzymes, tested falsely positive with the eCIM initially but eCIM negative upon repeat testing.