HCWs undergoing COVID-19 serological testing in the four participating hospitals
| FJD | HURJC | HUIE | HGV | All hospitals | |
| n (%) | n (%) | n (%) | n (%) | N (%) | |
| Total HCWs | 3696 (51.90) | 1693 (23.77) | 873 (12.26) | 859 (12.06) | 7121 (100) |
| HCWs with prior RT-PCR COVID-19 diagnosis | 463 (12.53) | 137 (8.09) | 93 (10.65) | 84 (9.78) | 777 (10.91) |
| HCWs eligible for the study | 3233 (87.47) | 1556 (91.91) | 780 (89.35) | 775 (90.22) | 6344 (89.09) |
| Participation in screening of eligible HCWs | 3091 (95.61) | 1482 (95.24) | 723 (92.69) | 699 (90.19) | 5995 (94.50) |
FJD, Fundación Jiménez Díaz; HCW, healthcare worker; HGV, Hospital General de Villalba; HUIE, Infanta Elena University Hospital; HURJC, Rey Juan Carlos University Hospital; RT-PCR, reverse transcriptase-PCR.