Effectiveness of using a face mask or respirator in indoor public places for the prevention of SARS-CoV-2 infection

The use of face masks or respirators (N95/KN95) is recommended to reduce the transmission of SARS-CoV-2, the virus that causes COVID-19 (1).

Well-fitting face masks and respirators effectively filter out virus-sized particles under laboratory conditions (2,3), although few studies have assessed their effectiveness in the real world in preventing the acquisition of SARS-CoV-2 infection (4).

A test-negative design case-control study recruited randomly selected California residents who had received a test result for SARS-CoV-2 between February 18 and December 1, 2021.

Use of a face mask or respirator was assessed among 652 case-participants (residents who had received positive test results for SARS-CoV-2) and 1,176 matched-control participants (residents who had received negative test results for SARS-CoV-2) who – reported having been in indoor public places in the 2 weeks prior to testing and who reported no known contact with anyone infected with SARS-CoV -2 confirmed or suspected during this period.

Always using a face mask or respirator in indoor public places was associated with a lower adjusted odds of a positive test result compared to never wearing a face mask or respirator in these settings (adjusted odds ratio [aOR] = 0.44; 95% CI = 0.24–0.82).

Among 534 participants who specified the type of face covering they usually wore, wearing N95/KN95 respirators (aOR = 0.17; 95% CI = 0.05 to 0.64) or surgical masks ( ORa = 0.34; 95% CI = 0.13 to 0.90) was associated with a significantly lower adjusted odds of a positive test result compared to no face mask or respirator.

These findings reinforce that in addition to being up to date with recommended COVID-19 vaccinations, consistently wearing a face mask or respirator in indoor public places reduces the risk of contracting SARS infection. -CoV-2. Using a respirator provides the highest level of personal protection against infection, although it is very important to wear a mask or respirator that is comfortable and can be used consistently.

This study used a test-negative case-control design, recruiting individuals with a positive (case-participants) or negative (control-participants) SARS-CoV-2 test result, among all California residents, without restriction of age, who received a molecular test result for SARS-CoV-2 from February 18 to December 1, 2021 (5).

Potential participants in the case were randomly selected from all people who received a positive test result in the previous 48 hours and were asked to participate by telephone.

For each enrolled case participant, investigators enrolled one control participant matched by age group, sex, and state region; thus, the investigators were not blinded to participants’ SARS-CoV-2 infection status.

Participants who reported having received a positive test result (molecular, antigenic or serological) or clinical diagnosis of COVID-19 were not eligible to participate. Between February 18 and December 1, 2021, a total of 1,528 case-participants and 1,511 control-participants were enrolled in the study among call attempts made to 11,387 case-participants and 17,051 control-participants ( response rates were 13.4% and 8.9%, respectively).

After obtaining informed consent from participants, the investigators administered a telephone questionnaire in English or Spanish.

All participants were asked if they had been to indoor public places (e.g. retail stores, restaurants or bars, recreation facilities, public transport, lounges, cinemas, worship services, schools, or museums) in the 14 days prior to testing and whether they wore a face mask or respirator all, most of the time, some of the time, or never in these settings.

Investigators recorded participants’ responses regarding COVID-19 vaccination status, socio-demographic characteristics, and history of exposure to anyone known or suspected to have been infected with SARS-CoV-2 within 14 days. preceding the participant test.

Participants registered from September 9 to December 1, 2021 (534) were also asked to indicate the type of face covering generally worn (N95/KN95 respirator, surgical mask or cloth mask) in indoor public places.

The main analysis compared self-reported use of a face mask or respirator in indoor public places 14 days before SARS-CoV-2 testing between case (652) and control (1,176) participants. Secondary analyzes considered consistency of face mask or respirator use all the time, most of the time, some, or never.

To understand the effects of masking on community transmission, the analysis included the subset of participants who, in the 14 days prior to their test, reported visiting indoor public places and reported no known exposures. to people known or suspected of having been infected with SARS. -CoV-2.

Additional analysis assessed differences in protection against SARS-CoV-2 infection by type of face covering worn and was limited to a subset of participants enrolled after September 9, 2021, who were asked for the type of face covering they typically wore. ; participants who reported usually wearing several different types of masks were categorized as wearing either a cloth mask (if they reported cloth mask use) or a surgical mask (if they did not declared the use of a cloth mask).

Adjusted odds ratios comparing mask-wearing history among case and control participants were calculated using conditional logistic regression.

Matching strata were defined by participants’ SARS-CoV-2 test week and county-level SARS-CoV-2 risk levels as defined under the Blueprint for Reopening Program. a Safer Economy of California.

Fitted models accounted for self-reported COVID-19 vaccination status (fully vaccinated with ≥2 doses of BNT162b2 [Pfizer-BioNTech] or mRNA-1273 [Moderna] or 1 dose of Ad.26.COV2.S [Janssen (Johnson & Johnson)] vaccine > 14 days prior to test versus zero dose), household income, race/ethnicity, age, gender, state region, and county population density.

Statistical significance was defined by two-sided Wald tests with p values ​​

This activity has been approved as public health surveillance by the California State Health and Human Services Agency Committee for the Protection of Human Subjects.

A total of 652 cases and 1176 control participants were enrolled in the study equally across nine multi-county regions of California (Table 1). The majority of participants (43.2%) identified as non-Hispanic white; 28.2% of participants identified as Hispanic (any race).

A higher proportion of case-participants (78.4%) were unvaccinated compared to control-participants (57.5%). Overall, 44 (6.7%) case participants and 42 (3.6%) control participants reported never wearing a face mask or respirator in indoor public places (Table 2), and 393 (60 .3%) case participants and 819 (69.6%) control participants reported always wearing a face mask or respirator in indoor public places.

Any use of a face mask or respirator in indoor public places was associated with a significantly lower likelihood of a positive test result compared to no use of a face mask or respirator (aOR = 0.51; 95% CI = 0.29-0.93).

Always using a face mask or respirator in indoor public places was associated with a lower adjusted odds of a positive test result compared to never wearing a face mask or respirator (aOR = 0, 44; 95% CI = 0.24–0.82); however, the adjusted odds of a positive test result suggest progressive reductions in protection among participants who reported wearing a face mask or respirator most of the time (aOR = 0.55; 95% CI = 0, 29-1.05) or part of the time (aOR = 0.71; 95% CI = 0.35 to 1.46) compared to participants who reported never wearing a face mask or respirator.

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Wearing an N95/KN95 respirator (aOR = 0.17; 95% CI = 0.05 to 0.64) or wearing a surgical mask (aOR = 0.34; 95% CI = 0 .13 to 0.90) was associated with a lower adjusted odds of a positive test result compared to not wearing a mask (Table 3). Wearing a cloth mask (aOR = 0.44; 95% CI = 0.17 to 1.17) was associated with a lower adjusted odds of a positive test compared to never wearing a cloth mask. face covering, but was not statistically significant.

Sara H. Byrd