Table 1.
Performance of a high-throughput neutralization test (HTNT) and a fluorescent focus neutralization (FFN) test for the detection of porcine epidemic diarrhea virus (PEDV)-neutralizing antibodies.
| Assay | Cutoff | Diagnostic sensitivity (%) | Diagnostic specificity (%) |
|---|---|---|---|
| HTNT (total fluorescence ratio*) | 70 | 97 (90, 99) | 95 (83, 99) |
| 75 | 97 (90, 99) | 98 (87, 100) | |
| 80 | 96 (90, 99) | 100 (91, 100) | |
| 85 | 95 (90, 98) | 100 (91, 100) | |
| 90 | 91 (83, 96) | 100 (91, 100) | |
| FFN (serum dilution†) | ≥1:20 | 98 (93, 100) | 98 (87, 100) |
| ≥1:40 | 96 (90, 99) | 100 (91, 100) | |
| ≥1:80 | 85 (76, 91) | 100 (91, 100) | |
| ≥1:160 | 72 (62, 80) | 100 (91, 100) | |
| ≥1:320 | 58 (47, 67) | 100 (91, 100) |
Estimates were based on receiver-operating characteristic curve (ROC) analyses of test results from PEDV-inoculated animals under the assumption that serum samples collected < 7 dpi were true negatives (n = 40) and serum samples collected ≥14 dpi were true positives (n = 99). Numbers in parentheses are 95% confidence intervals.
Sample total fluorescence intensity (TFI) was standardized as total fluorescence ratio (TFR), where TFR = 100 – ([average sample TFI × 100] ÷ average negative control TFI).
FFN neutralizing endpoint titers ≥1:20 were considered positive.12 Recommended cutoffs are highlighted in bold.