Questions about mask use keep filling my inbox. I’ve written before about when mask are most useful, and my general advice hasn’t changed much. However, some recent developments have make me think more about when and where more routine mask use might be of benefit.

Why are we re-thinking when to use masks?  What’s changed?

• There’s more SARS-CoV-2 transmission in the community in some areas. As that happens, simply identifying high risk people (e.g. travellers, those with known exposure) is less reliable for avoiding contact with the virus. The odds of anyone being infected get higher.
• People can be infectious for a short time before they get sick.
• There is increasing evidence that a fairly large percentage of infected (and infectious) people have asymptomatic infections (i.e. they don’t get sick but can still spread the virus).

These factors decrease our ability to confidently say “no, you’re probably not infected” about anyone; the more that happens, the more community measures such as routine mask use might make sense.

Key points to remember about masks and how they work:

• The most important point is that in most scenarios masks mainly help protect others from the wearer if the wearer is infected. Masks reduce the release of droplets (i.e. slightly larger liquid particles) and aerosols (i.e. very small liquid particles) when the wearer breathes, coughs or talks. (Both droplets and aerosols can can contain virus, but droplets don’t travel as far.)   Masks are generally less effective at protecting the wearer.
• The biggest benefit to the wearer might be preventing hand-to-mouth/nose contact, since we inadvertently do that all the time, and certainly increases the risk of exposure to whatever is on the person’s hands.  However, in some cases mask use can have the opposite effect if a person is constantly touching or readjusting their mask if doesn’t quite fit right or is uncomfortable.
• Surgical and N95 masks are in short supply in many areas. We need to conserve these supplies to make sure they are available where they’re truly needed (especially for front line medical workers who are at the highest risk).

The CDC has now recommended “wearing cloth face coverings in public settings where other social distancing measures are difficult to maintain (e.g., grocery stores and pharmacies), especially in areas of significant community-based transmission.” Other major public health organizations haven’t followed suit (yet). Whether that will follow or they will hold off because of the lack of clear benefit, and lack of mask supplies, remains to be seen.

What about routine mask use in veterinary clinics?

Most veterinary clinics are doing a great job of social distancing from owners. It’s tougher to maintain social distance between staff within a clinic, but there are some things we can do.  Unfortuantely the nature of veterinary care requires us to be in close proximity to others at times , because most of our patients require some kind of restraint for many routine procedures (e.g. drawing blood, placeing an intravenous catheter). This has led to a lot of discussion about staff routinely wearing masks in clinics. Again, masks mainly help protect others when the wearer is (either knowingly or unknowingly) infected.  Those known to be infected of course should not be in the clinic at all, but the concern is there may be more and more people who are unknowingly infected and not showing any signs.  Wearing a mask may make such a person less likely to infect others. For people like me who are frequent face-touchers (my own face… not others… just to be clear), there might be some additional personal protection. So, there are some valid reasons to have a mask use policy for situations where people have to get close, BUT masks should never be used as a crutch or a substitute for physical distancing whenever feasible, or proper attention to hand hygiene.

Nonetheless, I’m hesitant to burn through our limited supply of surgical masks when we (and human healthcare workers) might need them more later in higher-risk situations. Here’s where cloth masks might be useful. Reusable cloth masks are a reasonable option in lower-risk situations where the 2 m/6 ft barrier has to be broken, and they help conserve supplies of N95 and surgical masks for higher risk situations, as well as surgical procedures.

Do cloth masks work?

Maybe. The literature is pretty sparse and mixed, with some showing evidence of at least some level of protection, one study showing an increased risk of flu-like disease, and other studies showing the considerable variation in the ability of different materials to actually prevent the dispersal of droplets and aerosols.

A recent paper in Nature Medicine (Leung et al. 2020) showed that surgical masks significantly reduced detection of SARS-CoV-2 RNA in aerosols from exhaled breath of infected people (see graph below). There wasn’t a significant reduction in virus from larger droplets, which is a bit counter-intuitive, since masks should be better at retaining larger particles. However, the results were pretty close to being statistically significant and they didn’t actually detect any virus in droplets or aerosols from mask users. (The small sample size probably limited their ability to find a significant difference.) Whether these results apply to cloth masks is hard to say and is probably highly dependent on the material type (and how well the mask fits). However, it provides support for the potential protective effect when infected people wear good quality, well-fitted masks.

 So masks may be somewhat effective at reducing the risk of virus transmission between people in certain situations. On the other hand, if we’re not wasting needed healthcare supplies by using cloth masks, then there’s limited downsides if we also use some common sense about it.

Should veterinary staff routinely wear (cloth) masks in the clinic?

• It’s worth considering. From our veterinary infection control listserve, it seems like optional or mandatory mask use is becoming common in academic veterinary hospitals.
• Whether to make routine mask use mandatory or elective is an interesting question. Saying “go ahead and wear one if you want” is the easy approach, but that’s not as useful for something that’s designed to protect others from the wearer.  In other situations, if someone doesn’t follow a particular recommendation, they just put themselves at risk, but in this case the person not wearing the mask may be increasing the risk to others as well. If a facility is truly concerned (or is trying to allay staff concerns), it might need to be mandatory for everyone in order to avoid conflicts within the clinic between those who do and those who do not want to wear a mask.
• If mask use is going to be implemented for routine close contact procedures, cloth masks are a good way to preserve supplies. Rationing and reusing surgical masks has become a common approach, but that still depletes supplies pretty quickly, even if staff only get one mask per day or even every few days.

Even cloth masks are, not surprisingly, getting harder and harder to find. With the change in US CDC’s recommendation regarding routine use of cloth face coverings, I suspect they will become even more scarce.  Some clinics (and even community groups) are now making their own. There are lots of sewing patterns available online now, and the CDC even provides instructions for both sew and no-sew mask options.  I spent the evening playing around with designs and materials myself (see below).  FYI you can’t iron disposable surgical gown material – it will melt all over your iron.

Important reminder: Masks are not a cure-all. Wearing masks all the time while becoming lax at other critical practices (e.g. social distancing, hand hygiene) is counterproductive. Masks should be approached as something to use when social distancing isn’t possible, not as a means to avoid social distancing.