Table 2. Evaluation of ELISA assay performance and IgA and IgG seroprevalence, healthcare worker SARS-CoV-2 seroprevalence study, Ramat Gan, Israel, 4 April 2020–13 July 2020 (n = 428).
| Test performance | HCW seroprevalence | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Antibody type | Negative SARS-CoV-2a | Early positive COVID-19b | Positive COVID-19c | All HCW | HROW group | HRAW group | ||||||
| Positive /total |
Specificity (95% CI) | Positive/total | Sensitivity (95% CI) | Positive /total |
Sensitivity (95% CI) | Positive /total |
% (95% CI) | Positive/total | % (95% CI) | Positive/total | % (95% CI) | |
| IgA | 5/181 | 97.2 (93.3–98.9) | 34/69 | 49.2 (37.1–61.4) | 44/55 | 80 (66.6–89.1) | 27/428 | 6.3 (4.3–9.2) | 14/162 | 8.6 (5.2–14) | 2/97 | 2 (0.6–7.2) |
| IgG | 3/157 | 98 (94–99.5) | 19/69 | 27.5 (17.8–39.8) | 45/55 | 81.8 (68.6–90.4) | 3/428 | 0.7 (0.24–2) | 1/162 | 0.6 (0.1–3) | 0/97 | 0 (0–3.8) |
CI: confidence interval; COVID-19: coronavirus disease; HCW: healthcare worker; HRAW: high risk at work; HROW: high risk outside work; qRT-PCR: quantitative reverse transcription-polymerase chain reaction; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2.
a Sera before September 2019.
b Sera from qRT-PCR-positive COVID-19 individuals < 14 days.
c Sera from recovered COVID-19 individuals ≥ 14 days.