Table 1.
Study characteristics and main results from studies that assessed individual personal protective and environmental measures
| Reference, country | Study design | Public health measure | Sample size | Outcome measure | Study duration | Effect estimates: conclusions | Risk of bias |
|---|---|---|---|---|---|---|---|
| Doung-Ngern et al,63 Thailand | Case-control | Handwashing | 211 cases, 839 controls | Incidence | 1-31 Mar 2020 | Regular handwashing: adjusted odds ratio 0.34 (95% confidence interval 0.13 to 0.87): associated with lower risk of SARS-CoV-2* | Serious or critical |
| Lio et al,36 China | Case-control | Handwashing | 24 cases, 1113 controls | Incidence | 17 Mar-15 Apr 2020 | Adjusted odds ratio 0.30 (95% confidence interval 0.11 to 0.80): reduction in odds of becoming infectious* | Moderate |
| Xu et al,60 China | Cross sectional comparative | Handwashing | n=8158 | Incidence | 22 Feb-5 Mar 2020 | Relative risk 3.53 (95% confidence interval 1.53 to 8.15): significantly increased risk of infection with no handwashing* | Moderate |
| Bundgaard et al,66 Denmark | Randomised controlled | Mask wearing | 2392 cases, 2470 controls | Incidence | Apr and May 2020 | Odds ratio 0.82 (95% confidence interval 0.54 to 1.23): 46% reduction to 23% increase in infection* | Moderate |
| Doung-Ngern et al,63 Thailand | Case-control | Mask wearing | 211 cases, 839 controls | Incidence | 1-31 Mar 2020 | Adjusted odds ratio 0.23 (95% confidence interval 0.09 to 1.60): associated with lower risk of SARS-CoV-2 infection* | Serious or critical |
| Lio et al,36 China | Case-control | Mask wearing | 24 cases, 1113 controls | Incidence | 17 Mar-15 Apr 2020 | Odds ratio 0.30 (95% confidence interval 0.10 to 0.86): 70% risk reduction* | Moderate |
| Xu et al,60 China | Cross sectional comparative | Mask wearing | 8158 people | Incidence | 22 Feb-5 Mar 2020 | Relative risk 12.38 (95% confidence interval 5.81 to 26.36): significantly increased risk of infection* | Moderate |
| Krishnamachari et al,43 US | Natural experiment | Mask wearing | 50 states | Incidence (cumulative rate) | Apr 2020 | 3-6 months, adjusted odds ratio 1.61 (95% confidence interval 1.23 to 2.10): >6 months, 2.16 (1.64 to 2.88): higher incidence rate with later mask mandate than with mask mandate in first month* | Serious or critical |
| Wang et al,57 China | Retrospective cohort | Mask wearing | 335 people | Incidence (assessed as attack rate†) | 28 Feb-27 Mar 2020 | Odds ratio 0.21 (95% confidence interval 0.06 to 0.79): 79% reduction in transmission of SARS-CoV-2* | Moderate |
| Cheng et al,68 China | Longitudinal comparative | Mask wearing (South Korea v HKSAR) | 961 cases (HKSAR), average control not available | Incidence | 31 Dec 2019-8 Apr 2020 | Incidence rate 49.6% (South Korea) v 11.8% (HKSAR) P <0.001: 37.8% less SARS-CoV-2 cases* | Moderate |
| Leffler et al,49 US | Natural experiment | Mask wearing | 200 countries | Mortality (per capita) | Jan-9 May 2020 | No masks: mortality rate 61.9% (95% confidence interval 37.0% to 91.0%); masks: 16.2% (−14.4% to 57.4%): 45.7% fewer mortality* | Moderate |
| Lyu et al,50 US | Natural experiment | Mask wearing | 15 states | Case growth rate | 31 Mar-22 May 2020 | Mandatory mask wearing: case growth rate 2%: 2% decrease in daily covid-19 growth rate at ≥21 days (P<0.05)* | Moderate |
| Rader et al,45 US | Cross sectional | Mask wearing | 378 207 people | R0 | 3 Jun-27 Jul | Adjusted odds ratio 3.53 (95% confidence interval 2.03 to 6.43): 10% increase in self-reported mask wearing was associated with an increased odds of transmission control* | Moderate |
| Liu et al,58 US | Natural experiment | Mask wearing | 50 states | Rt | 21 Jan-31 May 2020 | Risk ratio 0.71 (95% confidence interval 0.58 to 0.75): 29% reduction in Rt* | Moderate |
| Wang et al,57 China | Retrospective cohort | Chlorine or ethanol based disinfectant | 335 people | Incidence (attack rate†) | 28 Feb-27 Mar 2020 | Odds ratio 0.23 (95% confidence interval 0.07 to 0.84): 77% reduction in transmission of SARS-CoV-2* | Moderate |
HKSAR=Hong Kong Special Administrative Region of China; R0=reproductive number; Rt=time varying reproductive number.
*
Interpretation of findings as reported in the original manuscript.
†
Percentage of individuals who tested positive over a specified period.