Table 2 Data summary and performance of the AT method compared with the reference test.
E. coli count (cfu 100 ml−1) risk category from reference methoda | AT, standard temperature incubation n = 945 | AT, ambient temperature incubation n = 945 | ||||||
|---|---|---|---|---|---|---|---|---|
100 ml | 10 ml | 100 ml | 10 ml | |||||
+ | − | + | − | + | − | + | − | |
<1 (n = 334) | 14 | 320 | 1 | 333 | 11 | 323 | 0 | 334 |
1–10 (n = 123) | 117 | 6 | 0 | 123 | 118 | 5 | 0 | 123 |
11–100 (n = 245) | 235 | 10 | 46 | 199 | 230 | 15 | 43 | 202 |
101+ (n = 243) | 241 | 2 | 205 | 38 | 243 | 0 | 209 | 34 |
Test accuracy statistics | ||||||||
Sensitivity: presence of E. coli (95% CI)a,b | 97.1% (95.4–98.2%) | 51.4% (46.9–56.0%) | 96.7% (95.0–98.0%) | 51.6% (47.1–56.2%) | ||||
Specificity: presence of E. coli (95% CI)a,b | 95.8% (93.1–97.7%) | 99.8% (98.8–100%) | 96.7% (94.2–98.3%) | 100% (99.2–100%) | ||||
Positive predictive value (PPV): presence of E. coli (95% CI)a,b | 97.7% (96.2–98.6%) | 99.6% (97.3–99.9%) | 98.2% (96.8–99.0%) | 100% | ||||
Percentage of total samples underestimating risk category a,b | 1.9% | 25% | 2.1% | 25% | ||||
Percentage of total samples overestimating risk category a,b | 1.5% | 0.11% | 1.2% | 0% | ||||
