TABLE 2.
Analytical sensitivitya
| IgG IIFT titer | No. of samples | A450-A620 cutoff | No. of positive samples, % sensitivity (95% CI), for ELISA 1 (sera, 1:100) | No. of positive samples, % sensitivity (95% CI), for ELISA 2 (sera, 1:2) | P |
|---|---|---|---|---|---|
| ≤80 | 7 | 0.200 | 0, 0.0 (0.0–40.4) | 4, 57.1 (25.0–84.2) | 0.0699 |
| 0.400 | 0, 0.0 (0.0–40.4) | 1, 14.3 (0.5–53.3) | 1.0000 | ||
| 160 | 17 | 0.200 | 6, 35.3 (17.2–58.8) | 13, 76.5 (52.2–90.9) | 0.0366 |
| 0.400 | 3, 17.6 (5.4–41.8) | 13, 76.5 (52.2–90.9) | 0.0016 | ||
| 320 | 22 | 0.200 | 14, 63.6 (42.9–80.4) | 21, 95.4 (76.5–100.0) | 0.0212 |
| 0.400 | 9, 40.9 (23.2–61.3) | 21, 95.4 (76.5–100.0) | 0.0002 | ||
| 640 | 25 | 0.200 | 20, 80.0 (60.4–91.6) | 24, 96.0 (78.9–100.0) | 0.1895 |
| 0.400 | 17, 68.0 (48.3–82.9) | 24, 96.0 (78.9–100.0) | 0.0232 | ||
| 1,280 | 19 | 0.200 | 19, 100.0 (80.2–100.0) | 19, 100.0 (80.2–100.0) | 1.0000 |
| 0.400 | 19, 100.0 (80.2–100.0) | 19, 100.0 (80.2–100.0) | 1.0000 | ||
| 2,560 | 11 | 0.200 | 10, 90.9 (60.1–100.0) | 11, 100.0 (70.0–100.0) | 1.0000 |
| 0.400 | 10, 90.9 (60.1–100.0) | 10, 90.9 (60.1–100.0) | 1.0000 | ||
| ≥5,120 | 8 | 0.200 | 8, 100.0 (62.8–100.0) | 8, 100.0 (62.8–100.0) | 1.0000 |
| 0.400 | 8, 100.0 (62.8–100.0) | 8, 100.0 (62.8–100.0) | 1.0000 | ||
a
Longitudinal serum samples obtained from 35 COVID-19 patients were stratified according to SARS-CoV-2 IgG IIFT titers (≤1 sample/patient/category). Sensitivities as well as 95% confidence intervals (CIs) were calculated for two alternative cutoff values (A450-A620 = 0.2 and 0.4). P values were determined using Fisher’s exact test.