Table 4.
Personal use of a face mask outside the home and risk of predicted Covid-19
| Personal use of a face mask a | |||
|---|---|---|---|
| Never | Ever b | P for interaction | |
| Overall | |||
| No. of Case/ Person-time (days) | 818/2494630 | 268/1190566 | |
| Model 1 HR (95% CI) c | 1 [Reference] | 0.35 (0.29–0.41) | |
| Model 2 HR (95% CI) d | 1 [Reference] | 0.35 (0.30–0.42) | |
| According to overall social distance grade of the community e | |||
| 0.57 f | |||
| Excellent/Good (A/B/C) | |||
| No. of Case/ Person-time (days) | 26/86375 | 7/43198 | |
| Model 1 HR (95% CI) | 1 [Reference] | 0.28 (0.10–0.76) | |
| Model 2 HR (95% CI) | 1 [Reference] | 0.31 (0.11–0.82) | |
| Fair (D) | |||
| No. of Case/ Person-time (days) | 137/553178 | 35/249104 | |
| Model 1 HR (95% CI) | 1 [Reference] | 0.29 (0.19–0.44) | |
| Model 2 HR (95% CI) | 1 [Reference] | 0.29 (0.19–0.45) | |
| Poor (F) | |||
| No. of Case/ Person-time (days) | 655/1855075 | 226/898262 | |
| Model 1 HR (95% CI) | 1 [Reference] | 0.36 (0.30–0.43) | |
| Model 2 HR (95% CI) | 1 [Reference] | 0.37 (0.30–0.44) | |
Abbreviations: HR (hazard ratio), CI (confidence interval)
Use of a face mask was collected from 139,690 participants beginning on June 12, 2020 based on the query “In the last week, did you wear a face mask when outside the house?”.
Ever wearing a face mask includes sometimes, most of the time, or always wearing a face mask as a time-varying variable.
Model 1 was stratified by age (<25, 25–34, 35–44, 45–54, 55–64, or ≥65), state, and calendar date at study entry.
Model 2 was stratified by age (<25, 25–34, 35–44, 45–54, 55–64, ≥65), state, and calendar date at study entry and further adjusted for race (white, black, Asian, or other), sex (male or female), population density (quartiles), current smoking, frontline healthcare worker, interaction with suspected or documented Covid-19, history of diabetes, heart disease, lung disease, and kidney disease (each yes or no).
Overall social distancing grades are denoted as Poor (F grade), Fair (D grade), Good (C grade), and Excellent (A+B grade). Overall social grade categories (A, B, C, D, and F) are provided by Unacast.
P for interaction was calculated based on Model 2.