Table 4 Personal use of a face mask outside the home and risk of predicted Covid-19.

From: Association of social distancing and face mask use with risk of COVID-19

 

Frequency of personal use of a face maska

 

None of the time

Sometimes

Most of the time

Always

P for trendb

Overall

 

  No. of cases/person-time (days)

813/2,488,940

42/197,995

115/530,749

224/991,553

 
 

  Model 1 HR (95% CI)c

1 [Reference]

0.28 (0.20–0.40)

0.33 (0.27–0.42)

0.35 (0.30–0.42)

1.29 × 10−33

 

  Model 2 HR (95% CI)d

1 [Reference]

0.27 (0.19–0.39)

0.34 (0.27–0.43)

0.36 (0.30–0.44)

7.59 × 10−32

According to overall social distance grade of the communitye

 Non-poor (A/B/C/D)

 

  No. of cases/person-time (days)

161/638,338

9/49,268

14/128,343

33/242,976

 
 

  Model 1 HR (95% CI)

1 [Reference]

0.26 (0.11-0.62)

0.24 (0.13–0.45)

0.26 (0.16–0.43)

1.70 × 10−9

 

  Model 2 HR (95% CI)

1 [Reference]

0.27 (0.11-0.66)

0.25 (0.13–0.48)

0.28 (0.17-0.45)

6.99 × 10−9

 Poor (F)

 

  No. of cases/person-time (days)

652/1,850,602

33/148,727

101/402,406

191/748,577

 
 

  Model 1 HR (95% CI)

1 [Reference]

0.28 (0.19–0.42)

0.36 (0.29–0.46)

0.37 (0.30–0.45)

5.70 × 10−26

 

  Model 2 HR (95% CI)

1 [Reference]

0.27 (0.18–0.41)

0.38 (0.30–0.48)

0.38 (0.31–0.46)

2.58 × 10−24

  1. HR hazard ratio, CI confidence interval.
  2. Cox proportional hazards regression models were used to calculate HRs and 95% CIs.
  3. aUse 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?”.
  4. bTwo-sided P values for trend were calculated as an ordinal variable.
  5. cModel 1 was stratified by age (<25, 25–34, 35–44, 45–54, 55–64, or ≥65), state, and calendar date at study entry.
  6. dModel 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).
  7. eOverall 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.
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