TABLE 1.
Comparison between Etest and the reference agar proportion method
| Antibiotic | Agreementa | Sensitivityb | Specificityc | PPVd | NPVe | Agreementa upon retesting |
|---|---|---|---|---|---|---|
| RIF | 97.9 (93/95) | 100.0 (21/21); 80.8–100.0 | 97.3 (72/74); 89.7–99.5 | 91.3 (21/23); 70.5–98.5 | 100.0 (72/72); 93.7–100 | 100.0 (95/95) |
| INH | 94.7 (90/95) | 94.6 (35/37); 80.5–99.1 | 94.8 (55/58); 84.7–98.7 | 92.1 (35/38); 77.5–97.9 | 96.5 (55/57); 86.8–99.4 | 97.9 (93/95) |
| EMB | 96.0 (92/95) | 85.7 (6/7); 42.0–99.2 | 97.7 (86/88); 91.3–99.6 | 75.0 (6/8); 35.6–95.5 | 98.9 (86/87); 92.9–99.9 | 100.0 (95/95) |
| STR | 85.3 (81/95) | 85.7 (18/21); 62.6–96.2 | 85.1 (63/74); 74.5–92.0 | 62.1 (18/29); 42.4–78.7 | 95.5 (63/66); 86.4–98.8 | 94.7 (90/95) |
| MDR (RIF and INH) | 98.9 (94/95) | 100.0 (21/21); 80.8–100.0 | 98.6 (73/74); 91.7–99.9 | 95.5 (21/22); 75.1–99.8 | 100.0 (73/73); 93.8–100.0 | 100.0 (95/95) |
| Any resistance (RIF, INH, EMB, or STR) | 93.7 (356/380) | 93.0 (80/86); 84.9–97.1 | 93.9 (276/295); 90.3–96.2 | 81.6 (80/98); 72.3–88.5 | 97.9 (276/282); 95.2–99.1 | 98.2 (373/380) |
Percent (number of concordant results/total results).
Ability of Etest to detect resistance, expressed as percent (number of isolates resistant by both methods/number resistant by the proportion method); 95% confidence interval.
Ability of Etest to detect susceptibility, expressed as percent (number of isolates susceptible by both methods/number susceptible by the proportion method); 95% confidence interval.
Positive predictive value, expressed as percent (number of isolates resistant by both methods/number resistant by Etest); 95% confidence interval.
Negative predictive value, expressed as percent (number of isolates susceptible by both methods/number susceptible by Etest); 95% confidence interval.