Table 3.
Association between exposure attributes and a contact’s positive test result
| Characteristic | Unadjusted RR (95% CI) | p-value | Adjusted RR* (95% CI) | p-value |
|---|---|---|---|---|
| Index case viral load at time of test (log10 RNA copies per mL of saliva) | 1.25 (1.06–1.46) | 0.007 | 1.27 (1.22–1.32) | p < 0.001 |
| Time between index case test and exposure (days) | 1.12 (1.10–1.15) | p < 0.001 | 1.14 (1.11–1.17) | p < 0.001 |
| Age of case (years) | 0.99 (0.94–1.04) | 0.7 | – | – |
| Case comorbidities | 0.89 (0.45–1.74) | 0.7 | – | – |
| Symptomatic status on day of exposure | ||||
| Asymptomatic | Reference | – | – | – |
| Pre-symptomatic | 2.23 (1.00–4.97) | 0.05 | – | – |
| Symptomatic | 2.05 (0.94–4.48) | 0.07 | – | – |
| Case had cough on day of exposure | 1.85 (1.15–2.99) | 0.01 | 1.41 (1.04–1.92) | 0.03 |
| Case congested or with runny nose on day of exposure | 1.46 (0.94–2.29) | 0.09 | – | – |
| Mask use | ||||
| No masks used | Reference | – | – | – |
| Case and/or contact wore a mask | 1.02 (0.59–1.78) | 0.9 | – | – |
| Duration (min) | ||||
| < 30 | Reference | – | – | – |
| ≥ 30 | 1.61 (0.84–3.09) | 0.1 | – | – |
| Location | ||||
| Outdoor | Reference | – | – | – |
| Indoor | 2.39 (0.69–8.24) | 0.2 | – | – |
| Contact type | ||||
| Non-physical contact | Reference | – | – | – |
| Physical contact | 2.14 (1.34–3.44) | 0.001 | 1.78 (1.26–2.53) | 0.001 |
| Contact relationship | ||||
| Household | Reference | – | – | – |
| Non-household | 1.19 (0.77–1.83) | 0.4 | – | – |
*Adjusted for viral load, time between index case test and exposure with contact, cough and contact type