Table 3.
Association of participants’ attributes with the likelihood of a positive result in the qualitative assay for the detection of immunoglobulin class G (IgG) against the nucleocapsid protein of SARS-CoV-2 (SARS-CoV-2 IgG-Abbott Laboratories) and with levels of receptor binding domain (RBD)-specific IgG antibodies (quantitative method; SARS-CoV-2 IgG II Quant-Abbott Laboratories). The analysis involved unvaccinated people with a self-reported history of laboratory-confirmed SARS-CoV-2 infection.
| IgG Test–Qualitative (S/C Index) (No History of Vaccination against COVID-19) |
IgG Test–Quantitative (AU/mL) (No History of Vaccination against COVID-19) |
|||||
|---|---|---|---|---|---|---|
| n = 622 | n = 969 | |||||
| ≥1.4 | <1.4 | p Value ¥ | OR (95% CI) | Median (IQR) | p Value ‡ | |
| Age | ||||||
| 0–19 | 10 (2.3) | 17 (8.7) | Ref | 425.4 (205.8–788.2) | ||
| 20–59 | 317 (73.6) | 159 (83.3) | 3.4 (1.5–7.6) | 353.3 (157.8–869.2) | ||
| ≥60 | 104 (24.1) | 15 (7.8) | <0.001 | 11.8 (4.6–30.5) | 1413.7 (567.4–3267.5) | <0.001 |
| Gender | ||||||
| Female | 242 (56.2) | 125 (65.5) | Ref | 368.3 (166.0–909.7) | ||
| Male | 189 (43.9) | 66 (34.5) | 0.030 | 1.5 (1.1–2.1) | 529.8 (206.8–1655.9) | <0.001 |
| Symptoms | ||||||
| Yes | 417 (96.8) | 170 (89.0) | 3.7 (1.8–7.4) | 441.8 (187.1–1165.6) | ||
| No | 14 (3.3) | 21 (11.0) | <0.001 | Ref | 264.2 (46.9–636.5) | 0.001 |
| Fever | ||||||
| Yes | 160 (37.1) | 51 (26.7) | 1.6 (1.1–2.4) | 577.5 (216.7–1866.8) | ||
| No | 271 (62.9) | 140 (73.3) | 0.011 | Ref | 374.5 (161.0–970.8) | <0.001 |
| Cough | ||||||
| Yes | 224 (52.0) | 66 | 2.0 (1.4–2.9) | 578.2 (223.3–1591.0) | ||
| (34.6) | ||||||
| No | 207 (48.0) | 125 (65.5) | <0.001 | Ref | 349.9 (153.6–829.8) | <0.001 |
| Shortness of breath | ||||||
| Yes | 121 (28.1) | 45 (23.6) | 1.3 (0.9–1.9) | 621.1 (216.7–1912.3) | ||
| No | 310 (71.9) | 146 (76.4) | 0.240 | Ref | 383.2 (166.0–966.7) | <0.001 |
| Muscle aches | ||||||
| Yes | 228 (52.9) | 89 (46.6) | 1.3 (0.9–1.8) | 418.8 (189.6–1164.9) | ||
| No | 203 (47.1) | 102 (53.4) | 0.147 | Ref | 443.4 (167.6–1122.0) | 0.862 |
| Sore throat | ||||||
| Yes | 133 (30.9) | 52 (27.2) | 1.2 (0.8–1.7) | 397.9 (186.5–1148.9) | ||
| No | 298 (69.1) | 139 (72.8) | 0.361 | Ref | 442.9 (178.4–1145.7) | 0.694 |
| Loss of taste | ||||||
| Yes | 222 (51.5) | 89 (46.6) | 1.2 (0.9–1.7) | 415.8 (184.7–1108.1) | ||
| No | 209 (48.5) | 102 (53.4) | 0.258 | Ref | 440.9 (175.4–1205.1) | 0.816 |
| Loss of smell | ||||||
| Yes | 244 (56.6) | 96 (50.3) | 1.3 (0.9–1.8) | 381.9 (170.7–1064.8) | ||
| No | 187 (43.4) | 95 (49.7) | 0.142 | Ref | 471.0 (194.8–1321.9) | 0.135 |
| Headache | ||||||
| Yes | 237 (55.0) | 97 (50.8) | 1.2 (0.8–1.7) | 427.1 (180.7–1144.6) | ||
| No | 194 (45.0) | 94 (49.2) | 0.332 | Ref | 439.7 (182.4–1204.7) | 0.877 |
| Fatigue | ||||||
| Yes | 284 (65.9) | 115 (60.2) | 1.3 (0.9–1.8) | 438.1 (186.5–1246.7) | ||
| No | 147 (34.1) | 76 (39.8) | 0.173 | Ref | 406.7 (170.4–1036.6) | 0.100 |
| Red feet toes | ||||||
| Yes | 3 (0.7) | 1 (0.5) | 1.3 (0.1–12.9) | 415.0 (236.0–814.4) | ||
| No | 428 (99.3) | 190 (99.5) | 0.639 | Ref | 432.1 (180.7–1148.9) | 0.947 |
| Nausea and Vomiting | ||||||
| Yes | 64 (14.9) | 17 (8.9) | 1.8 (1.2–3.1) | 460.9 (212.4–1538.8) | ||
| No | 367 (85.1) | 174 (91.1) | 0.042 | Ref | 425.4 (173.8–1108.1) | 0.109 |
| Diarrhea | ||||||
| Yes | 95 (22.0) | 35 (18.3) | 1.3 (0.8–1.9) | 666.8 (270.0–1602.2) | ||
| No | 336 (78.0) | 156 (81.7) | 0.293 | Ref | 384.7 (163.1–1038.3) | <0.001 |
| More than two Symptoms | ||||||
| Yes | 389 (89.4) | 152 (79.6) | 2.4 (1.5–3.8) | 443.4 (187.3–12,608.5) | ||
| No | 42 (10.6) | 39 (20.4) | <0.001 | Ref | 354.1 (115.1–758.0) | <0.001 |
| HCW | ||||||
| Yes | 52 (12.1) | 30 (15.7) | 0.7 (0.5–1.2) | 331.8 (136.7–850.9) | ||
| No | 379 (87.9) | 161 (84.3) | 0.216 | Ref | 441.8 (186.5–1166.7) | 0.048 |
| Hospital Admission | ||||||
| Yes | 34 (7.9) | 6 (3.1) | 2.6 (1.1–6.4) | 2832.2 (1325.5–4165.4) | ||
| No | 397 (92.1) | 185 (96.9) | 0.026 | Ref | 388.1 (171.8–989.0) | <0.001 |
| Difference between dates of reported 1st SARS-CoV-2 diagnostic test and IgG test | ||||||
| ≤1 month | 29 (6.7) | 7 (3.7) | 4.5 (1.6–12.5) | 447.9 (194.2–1318.2) | ||
| (1–3) months | 312 (72.6) | 97 (50.8) | 3.5 (1.9–6.6) | 488.5 (216.2–1365.5) | ||
| (3–6) months | 68 (15.8) | 64 (33.5) | 1.2 (0.6–2.3) | 341.6 (149.4–856.2) | ||
| >6 months | 21 (4.9) | 23 (12.0) | <0.001 | Ref | 327.3 (163.6–874.8) | <0.001 |
| Difference between dates of symptom onset and IgG test | ||||||
| ≤1 month | 30 (7.0) | 7 (3.7) | 5.5 (2.1–14.3) | 447.5 (207.6–1363.9) | ||
| (1–3) months | 303 (70.5) | 89 (46.6) | 4.4 (2.6–7.4) | 495.0 (222.6–1407.0) | ||
| (3–6) months | 66 (15.3) | 55 (28.8) | 1.5 (0.9–2.8) | 354.0 (153.6–894.4) | ||
| >6 months | 31 (7.2) | 40 (20.9) | <0.001 | Ref | 300.8 (120.8–890.0) | <0.001 |
S/C: signal/cut-off; AU: arbitrary units; HCW: health-care workers; ¥ p-value of chi-squared or fisher exact test; ‡ p-value of Kruskal–Wallis test or Mann–Whitney U test.