| 29 May 2020 to 3 Jul 2020 (n = 115) | 28 Aug 2020 to 25 Sep 2020 (n = 158) | 1 Dec 2020 to 15 Jan 2021 (n = 174) | 1 Mar 2021 to 23 Mar 2021 (n = 168) | p value |
---|---|---|---|---|---|
SARS-CoV-2 PCR | |||||
 Positive, N(%) | 9 (7.8) | 10 (6.3) | 5 (2.9) | 16 (9.5) | 0.085 |
 95% confidence interval | 3.6–14.3% | 3.1–11.3% | 1–6.6% | 5.5–15.0% | |
SARS-CoV-2 total antibodies | |||||
 Positive, N(%) | 13 (11.3) | 74 (46.8) | 80 (46.0) | 75 (44.6) |  < 0.001 |
 95% confidence interval | 6.5–18.6% | 38.9–54.9% | 38.4–53.7% | 37.0–52.5% | |
 Geometric mean, 95% CI (AU/mL)a | 31.1 (13.8, 70.0) | 29.4 (21.9, 39.4) | 26.7 (20.6, 34.8) | 13.1 (9.7, 17.8) |