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Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers : A Randomized Controlled Trial.
Ann Intern Med. 2021 03; 174(3):335-343.AIM

Abstract

BACKGROUND

Observational evidence suggests that mask wearing mitigates transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It is uncertain if this observed association arises through protection of uninfected wearers (protective effect), via reduced transmission from infected mask wearers (source control), or both.

OBJECTIVE

To assess whether recommending surgical mask use outside the home reduces wearers' risk for SARS-CoV-2 infection in a setting where masks were uncommon and not among recommended public health measures.

DESIGN

Randomized controlled trial (DANMASK-19 [Danish Study to Assess Face Masks for the Protection Against COVID-19 Infection]). (ClinicalTrials.gov: NCT04337541).

SETTING

Denmark, April and May 2020.

PARTICIPANTS

Adults spending more than 3 hours per day outside the home without occupational mask use.

INTERVENTION

Encouragement to follow social distancing measures for coronavirus disease 2019, plus either no mask recommendation or a recommendation to wear a mask when outside the home among other persons together with a supply of 50 surgical masks and instructions for proper use.

MEASUREMENTS

The primary outcome was SARS-CoV-2 infection in the mask wearer at 1 month by antibody testing, polymerase chain reaction (PCR), or hospital diagnosis. The secondary outcome was PCR positivity for other respiratory viruses.

RESULTS

A total of 3030 participants were randomly assigned to the recommendation to wear masks, and 2994 were assigned to control; 4862 completed the study. Infection with SARS-CoV-2 occurred in 42 participants recommended masks (1.8%) and 53 control participants (2.1%). The between-group difference was -0.3 percentage point (95% CI, -1.2 to 0.4 percentage point; P = 0.38) (odds ratio, 0.82 [CI, 0.54 to 1.23]; P = 0.33). Multiple imputation accounting for loss to follow-up yielded similar results. Although the difference observed was not statistically significant, the 95% CIs are compatible with a 46% reduction to a 23% increase in infection.

LIMITATION

Inconclusive results, missing data, variable adherence, patient-reported findings on home tests, no blinding, and no assessment of whether masks could decrease disease transmission from mask wearers to others.

CONCLUSION

The recommendation to wear surgical masks to supplement other public health measures did not reduce the SARS-CoV-2 infection rate among wearers by more than 50% in a community with modest infection rates, some degree of social distancing, and uncommon general mask use. The data were compatible with lesser degrees of self-protection.

PRIMARY FUNDING SOURCE

The Salling Foundations.

Authors+Show Affiliations

The Heart Center, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark (H.B., J.S.B., D.E.T., M.M.P., C.R.V., U.C.W., A.R.).The Heart Center, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark (H.B., J.S.B., D.E.T., M.M.P., C.R.V., U.C.W., A.R.).The Heart Center, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark (H.B., J.S.B., D.E.T., M.M.P., C.R.V., U.C.W., A.R.).Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark (C.V., T.T., H.U.).Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark (C.V., T.T., H.U.).Herlev & Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark (J.B.N., P.B.N., K.F., R.H., J.H.K., K.I.).The Heart Center, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark (H.B., J.S.B., D.E.T., M.M.P., C.R.V., U.C.W., A.R.).The Heart Center, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark (H.B., J.S.B., D.E.T., M.M.P., C.R.V., U.C.W., A.R.).Herlev & Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark (J.B.N., P.B.N., K.F., R.H., J.H.K., K.I.).The Heart Center, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark (H.B., J.S.B., D.E.T., M.M.P., C.R.V., U.C.W., A.R.).Herlev & Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark (J.B.N., P.B.N., K.F., R.H., J.H.K., K.I.).Herlev & Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark (J.B.N., P.B.N., K.F., R.H., J.H.K., K.I.).Herlev & Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark (J.B.N., P.B.N., K.F., R.H., J.H.K., K.I.).The Heart Center, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark (H.B., J.S.B., D.E.T., M.M.P., C.R.V., U.C.W., A.R.).Nordsjaellands Hospital, Hillerød, and Aalborg University Hospital, Aalborg, Denmark (M.P.A., C.T.).Centre for Diagnostics, Technical University of Denmark, Kongens Lyngby, Denmark (N.B.G.).National Influenza Center, Statens Serum Institut, Copenhagen, Denmark (R.T.).Technical University of Denmark, Kongens Lyngby, Denmark (K.S.).Center of Research & Disruption of Infectious Diseases, Amager and Hvidovre Hospital, Copenhagen University Hospital, Hvidovre, Denmark (T.B.).Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark (C.V., T.T., H.U.).Nordsjaellands Hospital, Hillerød, and Aalborg University Hospital, Aalborg, Denmark (M.P.A., C.T.).Herlev & Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark (J.B.N., P.B.N., K.F., R.H., J.H.K., K.I.).

Pub Type(s)

Journal Article
Randomized Controlled Trial
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

33205991

Citation

Bundgaard, Henning, et al. "Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers : a Randomized Controlled Trial." Annals of Internal Medicine, vol. 174, no. 3, 2021, pp. 335-343.
Bundgaard H, Bundgaard JS, Raaschou-Pedersen DET, et al. Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers : A Randomized Controlled Trial. Ann Intern Med. 2021;174(3):335-343.
Bundgaard, H., Bundgaard, J. S., Raaschou-Pedersen, D. E. T., von Buchwald, C., Todsen, T., Norsk, J. B., Pries-Heje, M. M., Vissing, C. R., Nielsen, P. B., Winsløw, U. C., Fogh, K., Hasselbalch, R., Kristensen, J. H., Ringgaard, A., Porsborg Andersen, M., Goecke, N. B., Trebbien, R., Skovgaard, K., Benfield, T., ... Iversen, K. (2021). Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers : A Randomized Controlled Trial. Annals of Internal Medicine, 174(3), 335-343. https://doi.org/10.7326/M20-6817
Bundgaard H, et al. Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers : a Randomized Controlled Trial. Ann Intern Med. 2021;174(3):335-343. PubMed PMID: 33205991.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers : A Randomized Controlled Trial. AU - Bundgaard,Henning, AU - Bundgaard,Johan Skov, AU - Raaschou-Pedersen,Daniel Emil Tadeusz, AU - von Buchwald,Christian, AU - Todsen,Tobias, AU - Norsk,Jakob Boesgaard, AU - Pries-Heje,Mia M, AU - Vissing,Christoffer Rasmus, AU - Nielsen,Pernille B, AU - Winsløw,Ulrik C, AU - Fogh,Kamille, AU - Hasselbalch,Rasmus, AU - Kristensen,Jonas H, AU - Ringgaard,Anna, AU - Porsborg Andersen,Mikkel, AU - Goecke,Nicole Bakkegård, AU - Trebbien,Ramona, AU - Skovgaard,Kerstin, AU - Benfield,Thomas, AU - Ullum,Henrik, AU - Torp-Pedersen,Christian, AU - Iversen,Kasper, Y1 - 2020/11/18/ PY - 2020/11/19/pubmed PY - 2021/3/24/medline PY - 2020/11/18/entrez SP - 335 EP - 343 JF - Annals of internal medicine JO - Ann Intern Med VL - 174 IS - 3 N2 - BACKGROUND: Observational evidence suggests that mask wearing mitigates transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It is uncertain if this observed association arises through protection of uninfected wearers (protective effect), via reduced transmission from infected mask wearers (source control), or both. OBJECTIVE: To assess whether recommending surgical mask use outside the home reduces wearers' risk for SARS-CoV-2 infection in a setting where masks were uncommon and not among recommended public health measures. DESIGN: Randomized controlled trial (DANMASK-19 [Danish Study to Assess Face Masks for the Protection Against COVID-19 Infection]). (ClinicalTrials.gov: NCT04337541). SETTING: Denmark, April and May 2020. PARTICIPANTS: Adults spending more than 3 hours per day outside the home without occupational mask use. INTERVENTION: Encouragement to follow social distancing measures for coronavirus disease 2019, plus either no mask recommendation or a recommendation to wear a mask when outside the home among other persons together with a supply of 50 surgical masks and instructions for proper use. MEASUREMENTS: The primary outcome was SARS-CoV-2 infection in the mask wearer at 1 month by antibody testing, polymerase chain reaction (PCR), or hospital diagnosis. The secondary outcome was PCR positivity for other respiratory viruses. RESULTS: A total of 3030 participants were randomly assigned to the recommendation to wear masks, and 2994 were assigned to control; 4862 completed the study. Infection with SARS-CoV-2 occurred in 42 participants recommended masks (1.8%) and 53 control participants (2.1%). The between-group difference was -0.3 percentage point (95% CI, -1.2 to 0.4 percentage point; P = 0.38) (odds ratio, 0.82 [CI, 0.54 to 1.23]; P = 0.33). Multiple imputation accounting for loss to follow-up yielded similar results. Although the difference observed was not statistically significant, the 95% CIs are compatible with a 46% reduction to a 23% increase in infection. LIMITATION: Inconclusive results, missing data, variable adherence, patient-reported findings on home tests, no blinding, and no assessment of whether masks could decrease disease transmission from mask wearers to others. CONCLUSION: The recommendation to wear surgical masks to supplement other public health measures did not reduce the SARS-CoV-2 infection rate among wearers by more than 50% in a community with modest infection rates, some degree of social distancing, and uncommon general mask use. The data were compatible with lesser degrees of self-protection. PRIMARY FUNDING SOURCE: The Salling Foundations. SN - 1539-3704 UR - https://www.unboundmedicine.com/medline/citation/33205991/Effectiveness_of_Adding_a_Mask_Recommendation_to_Other_Public_Health_Measures_to_Prevent_SARS_CoV_2_Infection_in_Danish_Mask_Wearers_:_A_Randomized_Controlled_Trial_ L2 - https://www.acpjournals.org/doi/10.7326/M20-6817?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub=pubmed DB - PRIME DP - Unbound Medicine ER -