TABLE 3.
Percentage of 2-fold dilution differences between the agar dilution modal MICs and the Etest modal MICs for proficiency panel isolates between 2003 and 2012
| Antibiotic | No. of isolatesa | No. of results (agar/Etest)b | % isolates (agar dilution modal MIC − Etest modal MIC) that differ by the following no. of 2-fold dilutions |
% agreement of modal MICs | Matched-pair t test, P < 0.05 of modal MIC means |
% concordance of interpretations | Modal MICs at categorical interpretation breakpointsc |
|||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ≤−2 | −1 | Same | 1 | ≥2 | t | P | Significant | % | No. | |||||
| Penicillin | 74 | 400/554 | 4.1 | 35.1 | 55.4 | 5.4 | 0.0 | 96.0 | 1.96 | 0.09525 | No | 94.5 | 43.6 | 34/78 |
| Tetracycline | 82 | 433/586 | 15.9 | 69.5 | 13.4 | 1.2 | 0.0 | 84.1 | 5.20 | <0.00001 | Yes | 79.3 | 67.9 | 57/84 |
| Erythromycin | 30 | 252/260 | 0.0 | 56.7 | 40.0 | 3.3 | 0.0 | 100.0 | −0.45 | 0.65312 | No | 69.6 | 73.3 | 22/30 |
| Spectinomycin | 66 | 324/314 | 3.0 | 42.4 | 53.0 | 1.5 | 0.0 | 97.0 | −0.15 | 0.87878 | No | 100.0 | 34.8 | 23/66 |
| Ceftriaxone | 90 | 398/641 | 3.3 | 35.6 | 52.2 | 8.9 | 0.0 | 96.7 | 4.27 | 0.00005 | Yes | 93.9 | 26.7 | 24/90 |
| Ciprofloxacin | 80 | 403/545 | 1.3 | 43.8 | 47.5 | 7.5 | 0.0 | 98.8 | −1.52 | 0.13336 | No | 93.2 | 27.5 | 22/80 |
| Cefixime | 27 | 272/310 | 0.0 | 40.7 | 51.9 | 7.4 | 0.0 | 100.0 | 2.39 | 0.02457 | Yes | 94.9 | 31.4 | 11/35 |
| Azithromycin | 62 | 275/626 | 0.0 | 12.9 | 71.0 | 16.1 | 0.0 | 100.0 | −0.04 | 0.96567 | No | 95.6 | 25.8 | 16/62 |
a
Number of isolates that have modal MICs for both the agar dilution method and the Etest method and can therefore be compared.
b
Total number of MIC values used to determine the modal MICs for both the agar dilution method and the Etest method.
c
The numbers of modal MICs at breakpoints for both Etest and agar dilution were calculated. The highest number of the 2 calculations was used.