Table 2.
Characteristics of SARS-CoV-2 test positive cases for delta variant* and test negative controls (two dose analysis). Values are numbers (percentages) unless stated otherwise
| Characteristics | Test positive (delta) (n=2027) | Test negative (n=10 135) | P value | Absolute standardized difference |
|---|---|---|---|---|
| Mean (SD) age at specimen collection date, years | 39.6 (14.7) | 40.6 (14.6) | 0.001 | 0.07 |
| Age at specimen collection date, years: | NA | NA | ||
| 18-44 | 1342 (66.2) | 6710 (66.2) | ||
| 45-64 | 564 (27.8) | 2820 (27.8) | ||
| 65-74 | 79 (3.9) | 395 (3.9) | ||
| ≥75 | 42 (2.1) | 210 (2.1) | ||
| Sex: | NA | NA | ||
| Female | 1133 (55.9) | 5665 (55.9) | ||
| Male | 894 (44.1) | 4470 (44.1) | ||
| Race/ethnicity: | NA | NA | ||
| Non-Hispanic white | 634 (31.3) | 3170 (31.3) | ||
| Non-Hispanic black | 309 (15.2) | 1545 (15.2) | ||
| Hispanic | 866 (42.7) | 4330 (42.7) | ||
| Non-Hispanic Asian | 75 (3.7) | 375 (3.7) | ||
| Other/unknown | 143 (7.1) | 715 (7.1) | ||
| Body mass index†: | 0.02 | 0.10 | ||
| <18.5 | 17 (0.8) | 118 (1.2) | ||
| 18.5 to <25 | 413 (20.4) | 2147 (21.2) | ||
| 25 to <30 | 568 (28.0) | 2872 (28.3) | ||
| 30 to <35 | 401 (19.8) | 2099 (20.7) | ||
| 35 to <40 | 214 (10.6) | 1071 (10.6) | ||
| 40 to <45 | 92 (4.5) | 505 (5.0) | ||
| ≥45 | 60 (3.0) | 305 (3.0) | ||
| Unknown | 262 (12.9) | 1018 (10.0) | ||
| Smoking†: | <0.001 | 0.10 | ||
| No | 1505 (74.2) | 7653 (75.5) | ||
| Yes | 312 (15.4) | 1717 (16.9) | ||
| Unknown | 210 (10.4) | 765 (7.5) | ||
| Charlson comorbidity score‡: | <0.001 | 0.14 | ||
| 0 | 1695 (83.6) | 7926 (78.2) | ||
| 1 | 192 (9.5) | 1249 (12.3) | ||
| ≥2 | 140 (6.9) | 960 (9.5) | ||
| Frailty index‡: | <0.001 | 0.16 | ||
| Quarter 1 | 536 (26.4) | 2504 (24.7) | ||
| Quarter 2 | 589 (29.1) | 2453 (24.2) | ||
| Quarter 3 | 489 (24.1) | 2551 (25.2) | ||
| Quarter 4 (most frail) | 413 (20.4) | 2627 (25.9) | ||
| Chronic diseases‡: | ||||
| Kidney disease | 37 (1.8) | 262 (2.6) | 0.04 | 0.05 |
| Heart disease | 21 (1.0) | 182 (1.8) | 0.01 | 0.06 |
| Lung disease | 142 (7.0) | 811 (8.0) | 0.13 | 0.04 |
| Liver disease | 25 (1.2) | 275 (2.7) | <0.001 | 0.12 |
| Diabetes | 127 (6.3) | 870 (8.6) | <0.001 | 0.09 |
| Immunocompromised§ | 49 (2.4) | 398 (3.9) | 0.001 | 0.09 |
| Autoimmune conditions‡ ¶ | 46 (2.3) | 252 (2.5) | 0.56 | 0.01 |
| Pregnant at specimen collection date | 51 (2.5) | 521 (5.1) | <0.001 | 0.14 |
| History of SARS-CoV-2 infection** | 16 (0.8) | 758 (7.5) | <0.001 | 0.34 |
| History of SARS-CoV-2 molecular test** | 1063 (52.4) | 4973 (49.1) | 0.006 | 0.07 |
| No of outpatient and virtual visits‡: | <0.001 | 0.28 | ||
| 0 | 235 (11.6) | 689 (6.8) | ||
| 1-4 | 704 (34.7) | 2816 (27.8) | ||
| 5-10 | 555 (27.4) | 2847 (28.1) | ||
| ≥11 | 533 (26.3) | 3783 (37.3) | ||
| No of emergency department visits‡: | 0.001 | 0.09 | ||
| 0 | 1698 (83.8) | 8163 (80.5) | ||
| 1 | 241 (11.9) | 1370 (13.5) | ||
| ≥2 | 88 (4.3) | 602 (5.9) | ||
| No of hospital admissions‡: | 0.07 | 0.06 | ||
| 0 | 1944 (95.9) | 9649 (95.2) | ||
| 1 | 76 (3.7) | 404 (4.0) | ||
| ≥2 | 7 (0.3) | 82 (0.8) | ||
| Preventive care‡ | 1019 (50.3) | 6459 (63.7) | <0.001 | 0.27 |
| Medicaid | 243 (12.0) | 1043 (10.3) | 0.02 | 0.05 |
| Neighborhood median household income: | 0.31 | 0.05 | ||
| <$40 000 | 90 (4.4) | 533 (5.3) | ||
| $40 000-$59 999 | 410 (20.2) | 2186 (21.6) | ||
| $60 000-$79 999 | 530 (26.1) | 2572 (25.4) | ||
| ≥$80 000 | 996 (49.1) | 4837 (47.7) | ||
| Unknown | 1 (0.0) | 7 (0.1) | ||
| KPSC physician/employee | 77 (3.8) | 462 (4.6) | 0.13 | 0.04 |
| Month of specimen collection: | <0.001 | 0.26 | ||
| March 2021 | 0 (0.0) | 0 (0.0) | ||
| April 2021 | 4 (0.2) | 20 (0.2) | ||
| May 2021 | 38 (1.9) | 227 (2.2) | ||
| June 2021 | 339 (16.7) | 2770 (27.3) | ||
| July 2021 | 1646 (81.2) | 7118 (70.2) | ||
| Specimen type: | <0.001 | 0.45 | ||
| Nasopharyngeal/oropharyngeal swab | 1960 (96.7) | 8460 (83.5) | ||
| Saliva (asymptomatic) | 67 (3.3) | 1675 (16.5) |
Medical center area not shown. Distribution of cases and controls across medical center areas differed.
KPSC=Kaiser Permanente Southern California; NA=not applicable.
Delta variant lineages: AY.1, AY.2, AY.3, B.1.617.2.
Defined in two years before specimen collection date.
Defined in one year before specimen collection date.
Defined as HIV/AIDS; leukemia/lymphoma, congenital and other immunodeficiencies, asplenia/hyposplenia; organ transplant; immunosuppressant drugs.
Defined as rheumatoid arthritis, inflammatory bowel disease, psoriasis and psoriatic arthritis, multiple sclerosis, systemic lupus erythematosus.
Defined on basis of all available medical records from 1 March 2020 to specimen collection date.