Respiratory virus shedding in exhaled breath and efficacy of face masks
Authors: Yuguo Li
Hui-Ling Yen
Eunice Y C Shiu
Donald K Milton
Benjamin J Cowling
J S Malik Peiris
Gabriel M Leung
Benien J P Hau
Dennis K M Ip
Kwok-Hung Chan
Daniel K W Chu
Wing-Hong Seto
Nancy H L Leung
James J McDevitt
Journal: Nature Medicine (2020)
Discipline: MOLECULAR BIOLOGY & GENETICS
Keywords: seasonal human coronaviruses; influenza viruses; rhinoviruses; exhaled breath; coughs
Affiliations: WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China., Department of Microbiology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China., Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA., Department of Surgery, Queen Mary Hospital, Hong Kong, China., Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, China., Department of Pathology, Hong Kong Baptist Hospital, Hong Kong, China., Maryland Institute for Applied Environmental Health, School of Public Health, University of Maryland, College Park, MD, USA., WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China. .

Abstract:  We identified seasonal human coronaviruses, influenza viruses and rhinoviruses in exhaled breath and coughs of children and adults with acute respiratory illness. Surgical face masks significantly reduced detection of influenza virus RNA in respiratory droplets and coronavirus RNA in aerosols, with a trend toward reduced detection of coronavirus RNA in respiratory droplets. Our results indicate that surgical face masks could prevent transmission of human coronaviruses and influenza viruses from symptomatic individuals. 

Retracted: No

PubPeer comments:
 The study was probably planned but not registered as a simple cross-over study on the efficiency of face mask. This looks like a violence of ICMJE guidelines, which recommend that all medical journals require registration of clinical trials in a public trials registry at or before the time of first patient enrolment as a condition of consideration for publication.  The ICMJE defines a clinical trial as any research project that prospectively assigns people or a group of people to an intervention, with or without concurrent comparison or control groups, to study the relationship between a health-related intervention and a health outcome. Face mask is an intervention, isn t it? The ability of a proband to generate aerosol depends heavily on virus type, location of infection and current virus replication rate. If these factors cannot be controlled, even a redefinition of the initial study design as a RCT does not make so much sense, in particular as sample size and power calculation would be wrong. Children and one sex is severely underrepresented and only 50% of probands have RT-PCR confirmed infections. Why showing also only results categorized by particle size? There are may reasons [why continuous data should not categorized](http: dx.doi.org 10.1300 J045v08n01_06). There is also a major misnomer: aerosol is the suspension of fine solid particles or liquid droplets in air or another gas while 5um does not differentiate between  droplets or  particles . Why are these data being published now 4 years after the study? , 
 *Face mask is an intervention, isn t it?* If they were asked to wear this out-and-about as a method to prevent infection, yes. But for the purposes of breathing into a funnel for particulate collection, no, it s not a medical intervention. *Why showing also only results categorized by particle size? There are may reasons why continuous data should not categorized.* While aerosol particulate can have continuous sizing, the behavior of these particles varies by size. The binning is based on that principle, which is an excellent reason to categorize by particle size. *There is also a major misnomer: aerosol is the suspension of fine solid particles or liquid droplets in air or another gas while 5um does not differentiate between  droplets or  particles .* The 5um particulate size does distinguish between respiratory droplets and fine-particle aerosol. As such the author use is not a misnomer and is moreover widely accepted terminology in the field. , 
  27 May 2020 An amendment to this paper has been published and can be accessed via a link at the top of the paper. https: www.nature.com articles s41591-020-0843-2#change-history Author correction:  In the version of this article initially published, in the first sentence of the third paragraph of the discussion, u201cfor rhinovirus we detected virus in aerosols in 19 of 34 (56%) participants (compared to 4 of 10 (40%) for influenza and 8 of 23 (35%) for coronavirus)u201d should have read u201cfor rhinovirus we detected virus in aerosols in 19 of 34 (56%) participants (compared to 4 of 10 (40%) for coronavirus and 8 of 23 (35%) for influenza),u201d with u2018influenzau2019 and u2018coronavirusu2019 transposed. The error has been corrected in the HTML and PDF versions of the article. https: www.nature.com articles s41591-020-0946-9 , 
 I wonder if the title is not incomplete, as they observed mainly virus in respiratory droplets aerosols from people that were coughing:  A subset of participants (72 of 246, 29%) did not cough at all during at least one exhaled breath collection, including 37 of 147 (25%) during the without-mask and 42 of 148 (28%) during the with-mask breath collection. In the subset for coronavirus (nu2009=u20094), we did not detect any virus in respiratory droplets or aerosols from any participants. In the subset for influenza virus (nu2009=u20099), we detected virus in aerosols but not respiratory droplets from one participant. In the subset for rhinovirus (nu2009=u200917), we detected virus in respiratory droplets from three participants, and we detected virus in aerosols in five participants. The title suggests (mainly to non-experts and media) that people were just breathing. Shouldn t the title include something like  exhaled breath and coughs ? On the other hand, I think that this is a quite balanced paper with a nice discussion. Thanks to the authors for that. ,