Table 1. Demographics and SARS-CoV-2 transmission characteristics by survey group.
| Characteristics | Cases (n=8913) | Negative controls (n=34 063) | Untested controls (n=25 989) | Total (n=68 965) |
| Age, median (IQR) | 43 (29, 55) | 44 (30, 54) | 45 (31, 55) | 44 (30, 55) |
| Sex, n (%) | ||||
| Female | 5065 (56.8) | 19 745 (58.0) | 15 816 (60.9) | 40 626 (58.9) |
| Male | 3848 (43.2) | 14 318 (42.0) | 10 173 (39.1) | 28 339 (41.1) |
| Ethnicity, n (%) | ||||
| Danish | 7640 (85.7) | 30 334 (89.1) | 24 668 (94.9) | 62 642 (90.8) |
| Other | 1273 (14.3) | 3729 (10.9) | 1321 (5.1) | 6323 (9.2) |
| Household size, n (%) | ||||
| 1–2 persons | 5234 (59.7) | 19 438 (57.8) | 16 246 (63.0) | 40 918 (60.0) |
| 3–4 persons | 2931 (33.4) | 12 156 (36.1) | 8290 (32.2) | 23 377 (34.3) |
| ≥5 persons | 606 (6.9) | 2046 (6.1) | 1241 (4.8) | 3893 (5.7) |
| Missing | 142 | 423 | 212 | 777 |
| Primary employment, n (%) | ||||
| Student | 746 (9.4) | 2734 (8.7) | 3617 (14.8) | 7097 (11.1) |
| Public employee | 1111 (14.0) | 4059 (12.9) | 2570 (10.5) | 7740 (12.1) |
| Private employee | 2545 (32.1) | 10 210 (32.4) | 4848 (19.9) | 17 603 (27.6) |
| Self-employed | 2739 (34.5) | 11 352 (36.0) | 10 127 (41.5) | 24 218 (37.9) |
| Non-employed | 529 (6.7) | 2036 (6.5) | 1988 (8.2) | 4553 (7.1) |
| Other | 264 (3.3) | 1134 (3.6) | 1237 (5.1) | 2635 (4.1) |
| Missing | 979 | 2538 | 1602 | 5119 |
| Type of occupation, n (%) | ||||
| Non-employed | 847 (10.7) | 3132 (10.0) | 3999 (16.5) | 7978 (12.6) |
| At home | 1470 (18.6) | 7673 (24.5) | 6858 (28.3) | 16 001 (25.2) |
| Own office | 601 (7.6) | 2477 (7.9) | 1916 (7.9) | 4994 (7.9) |
| Shared office | 1358 (17.2) | 5029 (16.0) | 4134 (17.1) | 10 521 (16.6) |
| Retail, library and factory work | 558 (7.1) | 1814 (5.8) | 1946 (8.0) | 4318 (6.8) |
| Social care and education | 1489 (18.9) | 5012 (16.0) | 1714 (7.1) | 8215 (12.9) |
| Healthcare sector | 746 (9.4) | 3098 (9.9) | 708 (2.9) | 4552 (7.2) |
| Transport (eg, bus/taxi driver) | 63 (0.8) | 240 (0.8) | 192 (0.8) | 495 (0.8) |
| Outdoors (eg, gardener) | 178 (2.3) | 714 (2.3) | 792 (3.3) | 1684 (2.7) |
| Other | 587 (7.4) | 2193 (7.0) | 1953 (8.1) | 4733 (7.5) |
| Missing | 1016 | 2681 | 1777 | 5474 |
| Contact with SARS-CoV-2 positive, n (%) | ||||
| None | 4025 (48.7) | 22 320 (68.0) | 24 166 (94.9) | 50 511 (75.9) |
| Other contact | 1715 (20.8) | 5683 (17.3) | 815 (3.2) | 8213 (12.3) |
| Close contact (<2 m, >30 min) | 2522 (30.5) | 4829 (14.7) | 477 (1.9) | 7828 (11.8) |
| Missing | 651 | 1231 | 531 | 2413 |
| Test reason, n (%) | ||||
| Symptoms | 3323 (40.0) | 5471 (16.7) | ||
| SARS-CoV-2 contact tracing app | 57 (0.7) | 1814 (5.5) | ||
| Prior to medical treatment | 85 (1.0) | 1982 (6.0) | ||
| Contact with SARS-CoV-2 positive | 3678 (44.3) | 9288 (28.3) | ||
| Work-related test reason | 260 (3.1) | 2889 (8.8) | ||
| Visit high risk person | 71 (0.9) | 2026 (6.2) | ||
| Travel plans | 25 (0.3) | 668 (2.0) | ||
| Prior to social event | 113 (1.4) | 2086 (6.4) | ||
| Suspected infection | 197 (2.4) | 1223 (3.7) | ||
| Other | 489 (5.9) | 5382 (16.4) | ||
| Missing | 615 | 1234 | ||
| Presumed source of infection, n (%) | ||||
| Unknown | 2876 (34.8) | |||
| Household | 0 (0.0) | |||
| Family/close friend | 2229 (27.0) | |||
| Colleague/acquaintance | 3152 (38.2) | |||
| Missing | 656 | |||