Characteristics of the study population
| Characteristic | 4–12 March | 14–22 April | 20–27 May | P value* |
| n=679 | n=608 | n=629 | ||
| Median age (IQR) | 45 (34–53) | 45 (34–54) | 45 (34–54) | – |
| Sex, n (%) | ||||
| Male | 166 (24.4) | 153 (25.2) | 154 (24.5) | – |
| Female | 513 (75.6) | 455 (74.8) | 475 (75.5) | |
| Occupational category, n (%) | ||||
| Nurse | 247 (36.4) | 215 (35.4) | 232 (36.9) | |
| Medical doctor | 206 (30.3) | 194 (31.9) | 194 (31) | – |
| Other healthcare service worker | 75 (11.0) | 64 (10.5) | 70 (11) | |
| Health service workers (incl. cleaners) | 86 (12.7) | 76 (12.5) | 72 (11.4) | |
| Socioadministrative staff | 65 (9.6) | 59 (9.7) | 61 (9.7) | |
| Seniority, n (%) | ||||
| <1 year | 42 (6.2) | 36 (5.9) | 36 (5.7) | |
| 1–10 years | 214 (31.5) | 192 (31.6) | 202 (32.1) | |
| 11–30 years | 304 (44.8) | 274 (45.1) | 283 (45) | – |
| >30 years | 87 (12.8) | 81 (13.3) | 81 (12.9) | |
| NR | 32 (4.7) | 25 (4.1) | 27 (4.3) | |
| Married, n (%) | ||||
| Yes | 448 (66.0) | 411 (67.6) | 421 (66.9) | – |
| No | 231 (34.0) | 197 (32.4) | 208 (33.1) | |
| Children, n (%) | ||||
| Yes | 371 (54.6) | 334 (54.9) | 343 (54.5) | – |
| No | 308 (45.4) | 274 (45.1) | 286 (45.5) | |
| Symptoms in previous 30 days, n (%) | ||||
| No | 459 (67.6) | 500 (82.2) | 565 (89.8) | |
| Yes | 220 (32.4) | 108 (17.8) | 64 (10.2) | <0.001 |
| Contacts with infected relatives, n (%) | ||||
| No | 630 (92.8) | 541 (89.0) | 561 (89.2) | |
| Yes | 49 (7.2) | 67 (11.0) | 68 (10.8) | 0.006 |
| Contacts with patients with COVID-19, n (%) | ||||
| No | 472 (69.5) | 207 (34.0) | 223 (35.4) | |
| Yes | 207 (30.5) | 401 (66.0) | 406 (64.5) | <0.001 |
| Trained in PPE use, n (%) | ||||
| No | 261 (38.4) | 137 (22.5) | 142 (22.6) | |
| Yes | 418 (61.6) | 471 (77.5) | 487 (77.4) | <0.001 |
| Confidence with PPE, n (%) | ||||
| Low/medium | 331 (48.7) | 172 (28.3) | 194 (30.8) | |
| High/very high | 332 (48.9) | 436 (71.7) | 435 (69.2) | <0.001 |
| NR | 16 (2.4) | – | – | |
| SARS-CoV-2 Ab status, n (%) | ||||
| Negative | 676 (99.6) | 582 (95.7) | 600 (95.4) | |
| Positive | 3 (0.4) | 26 (4.2) | 29 (4.6) | <0.001 |
| Newly detected positivity | 3 (0.4) | 23 (3.8) | 3 (0.5) |
*P value for trend obtained by a generalised linear multilevel model analysis.
NR, not reported; PPE, personal protective equipment.