Anonymous wrote:
Darren,
As for this test of clots for home-made facemasks; is that of no value?
https://smartairfilters.com/en/blog/best-materials-make-diy-face-mask-virus/
Arne
Oh Arne, I really do hope we get a chance to have a beer some day, I think we share curiosity and commitment. I think the short answer is that the filtering efficiency of the material is only a small part of the equation of whether a mask is worthwhile or not.
I expect most of you won't read below this line. If you intend to, I would suggest you get a beer, I certainly had some while I composed it.
If you like I can dig up the numbers, regarding filtration efficiency, vs coarse droplets and aerosols. I can't remember the numbers off the top of my head. Cloth masks definitely placed a distant last, even compared to surgical masks, which are a poor cousin to N95 masks. There is some data on this because it would be so attractive if cloth masks could be reused in the developing world, unfortunately the conclusions were that cloth masks were sufficiently permeable not to be effective.
However, I also think figuring out the filtration efficiency of a cloth mask is the wrong question to ask. I've now read more papers than I care to about masks. The field is full of research that looks at particle sizes because these are easy to measure. With the advent of PCR RNA testing, you also find studies that can now identify viruses on all sorts of surfaces and even in air samples. However, this is just the trace DNA of the virus and it may very well not be infectious at all.
I think the endpoint of a study on mask usefulness needs to be how you keep as many people as healthy as you can. Thus, the most sensible endpoint to measure is how many people get sick from a randomly selected group of folks assigned to either wear a particular mask or not wear a mask. Or as they did in a flu study, how many people around an infected person get sick if the infected person wears a mask. Such studies not only account for filtration efficiency and viability of virus particles but also social behaviour and how effectively the masks are worn. Sadly, there is not a good study that addresses this exact question for Covid-19. There are lots of ways mask wearing can be ineffective. Different diseases spread differently, most important is the minimum droplet size the virus remains viable in and whether the disease can spread by aerosol (very tiny droplets that float in the air rather than settling out). If the disease can spread by aerosol then a cloth mask is about as useful as breathing through mosquito screen (please excuse the slight exaggeration) both for reducing the spread of particles and for protecting you. Similarly, if a mask works perfectly, but you contaminate yourself as you put it on, or remove it, the overall protection is still nil. Or, if you think you can safely cough into the mask, but it is still allowing significant particles out, you can unintentionally infect others. The list is long, but I'm sure you get the point that the filtering efficiency of the mask is only one element in the equation.
Almost all the news reports lately that support the use of masks fail to consider that there are ways where masks can also decrease safety. One of the studies I cited here earlier showed that respiratory infections were worse amongst hospital workers who properly and regularly wore cloth facemasks compared to their coworkers that sometimes wore surgical masks and sometimes didn't wear a mask at all. That study included Coronavirus, but not the Covid-19 version. Another study showed a statistically insignificant difference of risk to family members catching the flu whether or not an infected member wore a mask. The researchers in that study thought small samples sizes were the reason they didn't see a significant result, but with over 120 patients in each group, if there were much of an effect they should have seen it. If you're expecting to protect others, but not really doing it, that is also a problem.
It is the entire system that matters. For an example, as you watch the news tonight, or on your next shopping trip, watch for the person that pulls their surgical mask down over their chin to talk or take a breathing break. Pulling the inside of their mask down over their dirty chin/neck, which they've likely touched while adjusting the mask, contaminates the inside of the mask. Even though it may be not a lot of contamination you have put it in a great environment to stay viable inside the mask. Every breath after that is a chance to breath it in and if they reuse the mask things get worse every time it goes on and off. Even for medical professionals trained in donning and doffing protective gear, the point of greatest risk is each time you remove or adjust a mask or other gear.
As you experienced with your mask experiments Arne, as the filtration efficiency gets better, it gets harder to breath. As it gets harder breath people find masks less comfortable to wear and thus adjust them more regularly and are less compliant with wearing a mask as they should. So, you end up with either a mask that doesn't filter very well and people wear, or you get masks that filter well, but that even many medical personal don't like to wear for a long time due to discomfort and greater difficulty breathing.
I wish masks worked better, it would be so nice to have a solution that would keep people safer and allow everyone to get back to work sooner.
I'm really fortunate to live in place where the politicians have got out of the way and turned the decisions over to the medical professionals. As you can imagine, the Canadian public has had quite a few questions about mask use after the American presidential and CDC recommendations. Today our provincial health officer (an exceptionally reasonable, science-based decision maker) announced (after our national review in response to the American recommendations on masks) that they are not recommending the use of face masks, but are being permissive about their use as long as they are not surgical or medical (N95) masks. Basically, cloth masks could be used if you are in a very crowded setting (which they say you shouldn't do anyway) or think there is a chance you could not be able to cough into the crook of your elbow should the need to cough arise (although you should not go out if you have any coughing). Here is a link to today's updated epidemic curve for BC, which is a place where a respected health officer has said masks are not necessary and a majority of people are not wearing masks. We have however, done quite a bit of testing (for a while our little province had done more than the entirety of the US), and we did start social distancing very early in our outbreak.
When we started this conversation, I was concerned that your use of the mask would encourage others (more those that saw you than those reading this thread) and that they would buy N95 or surgical masks that would further deplete the supply for healthcare workers. That now seems like a long time ago and increasingly such masks are being directed solely to healthcare providers, so this concern is now less relevant. I think the way you are using your mask is sensible Arne and given the messaging from many governments you certainly won't be alone. I think it would be nice if you could get some hand sanitizer to use after you remove the mask outside the grocery store and have quarantined the mask in a plastic baggie (or reusable Tupperware) until you can sterilise it.
I should also say that all this is relevant to the current circumstances most of us face which includes physical distancing and staying at home if you are sick. If I had to ride a packed subway train, with others that were coughing, or if I were coughing, then the scales probably tip in favour of wearing a mask, because all the most useful methods for reducing the spread of the virus have been lost and you're stuck with whatever you can do. A cloth mask would not be my first choice in this setting though. I suppose if I had no other options I'd sew a cloth mask and wear it knowing that I'd still have to do everything possible to make sure I didn't cough towards anyone or even in the direction of surfaces likely to be touched. Similarly, if I was somewhere where it was mandated to wear face protection, I'd do it for the importance of social cohesion, but I'd still be working harder at social distancing and hand washing.