Table 1.
Descriptive Attributes of Participants Reporting High-Risk Exposures
| Participant Attribute | All Participants | Casesa | Controlsb | |
|---|---|---|---|---|
| n (%) | n (%) | n (%) | ||
| N = 1006 | N = 751 | N = 255 | ||
| Age, years | ||||
| 0–6 | 37 (3.7) | 35 (4.7) | 2 (0.8) | |
| 7–12 | 61 (6.1) | 44 (5.9) | 17 (6.7) | |
| 13–17 | 67 (6.7) | 50 (6.7) | 17 (6.7) | |
| 18–29 | 299 (29.7) | 223 (29.7) | 76 (29.8) | |
| 30–49 | 352 (35.0) | 245 (32.6) | 107 (42.0) | |
| 50–64 | 136 (13.5) | 110 (14.6) | 26 (10.2) | |
| ≥65 | 54 (5.4) | 44 (5.9) | 10 (3.9) | |
| Sex | ||||
| Male | 460 (45.7) | 343 (45.7) | 117 (45.9) | |
| Female | 546 (54.3) | 408 (54.3) | 138 (54.1) | |
| Household income | ||||
| Less than $50 000 | 245 (24.4) | 187 (24.9) | 58 (22.7) | |
| $50 000–$100 000 | 232 (23.1) | 185 (24.6) | 47 (18.4) | |
| $100 000–$150 000 | 127 (12.6) | 79 (10.5) | 48 (18.8) | |
| More than $150 000 | 128 (12.7) | 88 (11.7) | 40 (15.7) | |
| Refuse | 170 (16.9) | 131 (17.4) | 39 (15.3) | |
| Not sure | 104 (10.3) | 81 (10.8) | 23 (9.0) | |
| Race/ethnicity | ||||
| Non-Hispanic White | 441 (45.7) | 331 (45.9) | 110 (44.9) | |
| Non-Hispanic Black | 45 (4.7) | 37 (5.1) | 8 (3.3) | |
| Hispanic (any race) | 253 (26.2) | 192 (26.6) | 61 (24.9) | |
| Asian | 83 (8.6) | 62 (8.6) | 21 (8.6) | |
| Native American | 17 (1.8) | 15 (2.1) | 2 (0.8) | |
| Native Hawaiian | 5 (0.5) | 5 (0.7) | 0 (0.0) | |
| More than 1 race | 122 (12.6) | 79 (11.0) | 43 (17.6) | |
| Refuse | 40 (4.0) | 30 (4.0) | 10 (3.9) | |
| Region of residencec | ||||
| Predominantly urban regions | ||||
| San Francisco Bay area | 108 (10.7) | 87 (11.6) | 21 (8.2) | |
| Greater Los Angeles area | 98 (9.7) | 76 (10.1) | 22 (8.6) | |
| Greater Sacramento area | 128 (12.7) | 99 (13.2) | 29 (11.4) | |
| San Diego and southern border | 96 (9.5) | 75 (10.0) | 21 (8.2) | |
| Predominantly rural regions | ||||
| Central Coast | 127 (12.6) | 89 (11.9) | 38 (14.9) | |
| Northern Sacramento Valley | 106 (10.5) | 80 (10.7) | 26 (10.2) | |
| San Joaquin Valley | 111 (11.0) | 78 (10.4) | 33 (12.9) | |
| Northwestern California | 116 (11.5) | 79 (10.5) | 37 (14.5) | |
| Sierras region | 116 (11.5) | 88 (11.7) | 28 (11.0) | |
| Vaccination statusd | ||||
| Unvaccinated | 649 (68.4) | 546 (75.3) | 103 (46.0) | |
| Partially vaccinated | 83 (8.7) | 56 (7.7) | 27 (12.1) | |
| Fully vaccinated | 217 (22.9) | 123 (17.0) | 94 (42.0) | |
| County reopening tiere | ||||
| Purple (most restrictive) | 201 (20.0) | 160 (21.3) | 41 (16.1) | |
| Red | 206 (20.5) | 166 (22.1) | 40 (15.7) | |
| Orange | 200 (19.9) | 165 (22.0) | 35 (13.7) | |
| Yellow (least restrictive) | 23 (2.3) | 17 (2.3) | 6 (2.4) | |
| After 15 June | 376 (37.4) | 243 (32.4) | 133 (52.2) | |
| Symptoms experienced | ||||
| No symptoms | 406 (40.4) | 206 (27.4) | 200 (78.4) | |
| At least 1 symptom | 600 (59.6) | 545 (72.6) | 55 (21.6) | |
| Level of anxiety about coronavirus disease 2019 | ||||
| Very anxious | 157 (15.6) | 108 (14.4) | 49 (19.2) | |
| Not very anxious | 849 (84.4) | 643 (85.6) | 206 (80.8) | |
Recent high-risk exposure is defined as reported contact with an individual known or suspected to have been infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at any time within the 14 days before participants were tested. Covariates with significant associations at a 2-sided P < .05 type 1 error rate include age (P = .01), income (P = .004), county reopening tier (P < .001), vaccination status (P < .001), and symptoms (P < .001), based on the χ2 test. Percentages presented in the table should be interpreted to represent the proportion of cases or controls with each characteristic and not their prevalence within the general population. Abbreviation: ref, reference.
Cases reporting high-risk exposure represent 51% of 1474 cases who enrolled in and successfully completed the study.
Controls reporting high-risk exposure represent 18% of 1447 controls who enrolled in and successfully completed the study.
We list counties grouped into each region in Supplementary Table 1.
We defined participants as fully vaccinated at the time of their test if >14 days had passed following receipt of a second dose of Pfizer/BioNTech BNT-162b2 or Moderna mRNA-1273 (108 cases, 686 controls) or a single dose of Jansen Pharmaceutical Companies JNJ-78436735 (15 cases, 8 controls). Participants who had received at least 1 dose of any coronavirus disease 2019 (COVID-19) vaccine but did not meet these criteria for fully vaccinated status were considered partially vaccinated (52 cases and 24 controls who received BNT162b2 or mRNA-1273; 4 cases and 3 controls who received JNJ-78436735). Participants who had not received any COVID-19 vaccine doses were considered unvaccinated.
The State of California implemented a tiered system of reopening to reduce risk of SARS-CoV-2 transmission in community settings. On 15 June 2021, California discontinued the tiered system, relaxed facial masking requirements in certain indoor settings, and allowed businesses to reopen without physical distancing restrictions. Numbers of participants enrolled by month (including after 15 June) are presented in Supplementary Table 3.