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Very nice work by the authors. Perhaps they could provide additional details about the methods used here to test particle filtration.
The suggestion that cloth masks can lead to increased infection compared to no mask is not substantiated The control arm had less than 1% of no mask use and therefore the statement is an assumption not a proof . It could be possible for bacteria or fungi that could multiply on the mask but for virus it would have to shown there is more bioavailability than no mask .
The authors do not state what kind / standard of cloth masks were used. Is there any chance they could do this. Given the huge shortage of FFP2 and FFP3 masks, it would be helpful to know the authors’ views of advice from the CDC in the US. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/diy-cloth...
I like the article. However, in my humble opinion, I wish there is a Material section in it describing the different types of fabrics the masks are made of. If circumstances do not permit detail descriptions of individual masks, it would generate more scientific value if the materials can be grouped and categorized, at least broadly, such as solid cotton sheet, gauze, etc. Similarly, statements, on the number of fabric layers in and photographs of the different shapes of representative groups of masks would be very useful.
Thank you for your work. It seems that in addition to healthcare workers, many people in the general population are referring to your research about cloth masks for guidance about homemade ("DIY")masks for use in the general population. If you are able to provide an addendum to your original research similar to this one addressing the question of their suitability for the general population that would be very helpful.
This is a critical study, being the only C-RCT to evaluate cloth masks, and it will carry inordinate weight until more studies are done. It makes findings and recommendations which have pretty drastic implications and gainsay widespread practice. It therefore is appropriate, I think to test it with some devil's advocate interrogation. I wish to raise 3 such arguments that I hope will generate debate.
1. The 2015 study shows that the cloth masks have higher rates of infection in the health workers (RR 1.51 for CRI, 1.72 for for lab confirmed infection). Actual infection rates were 7.6% versus 4.8%. But as the authors have stated, there was no no-mask control group. To quote the authors "The finding of a much higher rate of infection in the cloth mask arm could be interpreted as harm caused by cloth masks, efficacy of medical masks, or most likely a combination of both.” But why not draw the conclusion that the cloth masks are simply less effective at reducing infection.
For example, some studies indicate medical masks are highly effective – assume an 80% reduction of infection, for both N95 and surgical masks. If, say, out of 100 infections that would have occurred, medical masks prevented 80, resulting in 20 infections, and according to this study, cloth masks would result in 51% more (RR=1.51), i.e. 30 cases, or at upper limit of 95%CI, RR=2.49 i.e. 50 cases, then the cloth masks have still avoided between 50 and 70 cases, i.e. more than half...
For example, some studies indicate medical masks are highly effective – assume an 80% reduction of infection, for both N95 and surgical masks. If, say, out of 100 infections that would have occurred, medical masks prevented 80, resulting in 20 infections, and according to this study, cloth masks would result in 51% more (RR=1.51), i.e. 30 cases, or at upper limit of 95%CI, RR=2.49 i.e. 50 cases, then the cloth masks have still avoided between 50 and 70 cases, i.e. more than half the cases are prevented. Using the RR finding of 1.72 (upper 95%CI 2.94) for LCIs, the percent of cases avoided with cloth masks would be 66%, or at the minimum 41%. I recognise that the RR for ILIs was much higher and would defeat this argument, but it seems to me those are 'low certainty' figures based on very low numbers - only 2 cases in the reference group. But even if we used those RRs for ILIs, it would still not counter the argument for the other two.
2. The the main virus transmitted in this study was Rhinovirus (85%) – which is mostly airborne whereas WHO argues that SARS-CoV2 is mainly droplet or fomite/touch. (WHO 29/2/2020 Modes of Transmission) The effectiveness of transmission interruption by cloth masks is likely to be different and better for droplet versus airborne transmission.
3. The high penetration of the in vitro test of cloth masks (97%) is quite out of line with most other in vitro tests of cloth masks which usually show 50% to 70% blocking (see e.g. Davies A1, Thompson KA, Giri K, Kafatos G, Walker J, Bennett A. 2013 Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic? doi: 10.1017/dmp.2013.43.)
Critical shortages of personal protective equipment (PPE) have resulted in the US Centers for Disease Control downgrading their recommendations for health workers treating COVID-19 patients from respirators to surgical masks and finally to home-made cloth masks. As authors of the only published randomised controlled clinical trial of cloth masks, we have been getting daily emails about this from health workers concerned about using cloth masks. The study found that cloth mask wearers had higher rates of infection than even the standard practice control group of health workers, and the filtration provided by cloth masks was poor compared to surgical masks. At the time of the study, there had been very little work done in this space, and so little thought into how to improve the protective value of the cloth masks. Until now, most guidelines on PPE did not even mention cloth masks, despite many health workers in Asia using them.
Health workers are asking us if they should wear no mask at all if cloth masks are the only option. Our research does not condone health workers working unprotected. We recommend that health workers should not work during the COVID-19 pandemic without respiratory protection as a matter of work health and safety. In addition, if health workers get infected, high rates of staff absenteeism from illness may also affect health system capacity to respond. Some health workers may still choose to work in inadequate PPE. In this case, the physic...
Health workers are asking us if they should wear no mask at all if cloth masks are the only option. Our research does not condone health workers working unprotected. We recommend that health workers should not work during the COVID-19 pandemic without respiratory protection as a matter of work health and safety. In addition, if health workers get infected, high rates of staff absenteeism from illness may also affect health system capacity to respond. Some health workers may still choose to work in inadequate PPE. In this case, the physical barrier provided by a cloth mask may afford some protection, but likely much less than a surgical mask or a respirator.
It is important to note that some subjects in the control arm wore surgical masks, which could explain why cloth masks performed poorly compared to the control group. We also did an analysis of all mask wearers, and the higher infection rate in cloth mask group persisted. The cloth masks may have been worse in our study because they were not washed well enough – they may become damp and contaminated. The cloth masks used in our study were products manufactured locally, and fabrics can vary in quality. This and other limitations were also discussed.
There are now numerous reports of health workers wearing home made cloth masks, or re-using disposable mask and respirators, and asking for guidance. If health workers choose to work in these circumstances, guidance should be given around the use.
There have been a number of laboratory studies looking at the effectiveness of different types of cloth materials, single versus multiple layers and about the role that filters can play. However, none have been tested in a clinical trial for efficacy. If health workers choose to work using cloth masks, we suggest that they have at least two and cycle them, so that each one can be washed and dried after daily use. Sanitizer spray or UV disinfection boxes can be used to clean them during breaks in a single day. These are pragmatic, rather than evidence-based suggestions, given the situation.
Finally for COVID-19, wearing a mask is not enough to protect healthcare workers – use of gloves and goggles are also required as a minimum, as SARS-CoV-2 may infect not only through the respiratory route, but also through contact with contaminated surfaces and self-contamination.
Governments and hospitals should plan and stockpile proper disposable products such as respirators and surgical masks to ensure the occupational health and safety of health workers. This appears to have been a failure in many countries, including high income countries.