COVID-19 Series: Do Face Masks Work?

Did you ever think you would be worried – about petting your own dog or cat? Here is our first story.

Ideally, once you became infected, you would be safely quarantined away from your family in a so-called “fever clinic,” a dedicated facility designed to assess, test, treat, and triage patients, so you wouldn’t put the people you live with at risk. Fever clinics were one of the strategies used to bring the outbreak in China under control by preventing clusters of family infections. In lieu of such innovations, the best choice is to try to recover at home, isolated as much as possible from your housemates. Preferably, you should avoid contact with both people and pets, and be cordoned off in a “sick room” with a separate bathroom, if possible.

Can pets get the disease? In rare cases, dogs have been found infected with the new coronavirus, but the virus replicates poorly in canines. They don’t seem to get sick, and they don’t appear to pass the virus along to others. This is consistent with what we saw in SARS, where a small number of pets tested positive, but they didn’t appear able to infect others.

The COVID-19 virus has been shown to reproduce efficiently in cats, however, who are then able to experimentally transmit the virus to other cats in separate cages, presumably via respiratory droplets, even though they may themselves not become sick. A survey of 102 cats in Wuhan province after the outbreak found evidence of infection in 15 of them––presumed, as with the pet dogs, to be cases of human-to-animal transmission. In the United States, the first confirmed case of animal infection was a sickened tiger at the Bronx Zoo, followed by a few pet cats. There is no evidence to date that pets have been a source of infection of COVID-19 for humans, but rather, we suspect, it’s the other way around.

To reduce the risk of spreading the disease to those you live with if you are sick, cover your nose and mouth with a tissue when you cough or sneeze, throw the used tissue in a lined trash can, and then immediately sanitize your hands. Don’t share personal household items, such as eating utensils, towels, or bedding. Wash your hands often. Routinely disinfect all high-touch objects, such as phones, doorknobs, and toilet surfaces in your sick room and bathroom yourself, and have someone else clean and disinfect the rest of the house, if possible. Harvard public health experts suggest running the exhaust fan in the bathroom. Opening the windows in the sick room to enhance ventilation may also help. During the SARS outbreak, hospital wards with larger ventilation windows appeared to harbor significantly lower infection risk for healthcare workers. And finally, based on surrogate coronaviruses, using a humidifier if the air is dry may also cut down on the viral circulation.

Most people who contract COVID-19 spontaneously recover without the need for medical intervention. If you do come down with it, protect those around you, get rest, stay hydrated, and monitor your symptoms. If serious problems arise, such as difficulty breathing or persistent pain or pressure in the chest, seek medical attention—but, notify the 911 operator that you may have the virus, or if less serious, call your doctor or emergency room first for before heading in, since they may have special instructions for suspect cases in your area.

The CDC advises that once your symptoms start getting better, once you’ve been fever-free for three full days (off of fever-reducing medications), and it’s been at least a full week since your symptoms first started, then you can start relaxing your home isolation. The World Health Organization is more conservative, however, recommending self-quarantine for a full 14 days for anyone with symptoms, or anyone living with anyone with symptoms.

If you’re sick and you must be in the same room with someone else, you should wear a face mask. That’s what masks were originally designed for, so-called “source control,” rather than self-protection. They are meant to protect others from you, rather than you from others. Common cold coronaviruses (as well as flu and rhinoviruses) can be detected in exhaled breath, not just coughing and sneezing, and surgical masks can cut down on the amount of virus you exhale out into in the world. We have yet to know if this is true of COVID-19, but the head of the standing committee on Emerging Infectious Diseases at the National Academy of Sciences told the White House: “Currently available research supports the possibility that SARS-CoV-2 could be spread via bioaerosols generated directly by patients’ exhalation.”

This shouldn’t be surprising. After all, respiratory droplets are not just sneezed gobs of mucus. When your breath fogs when you’re outside on a really cold day, that’s an illustration of respiratory droplets. That plume of vapor coming out of your mouth is made up of tiny droplets of water straight from your lungs. On a warm day, you can imagine yourself breathing out that same cloud—you just can’t see it. Err on the side of caution, and assume the virus is in the breath.

If infected individuals are exhaling virus before they even know they have it, maybe everyone should be covering their face in public. The CDC initially resisted such a measure, a decision the director-general of the Chinese CDC referred to as a “big mistake.” The US CDC relented in April, recommending “wearing cloth face coverings in public settings where other social distancing measures are difficult to maintain,” such as grocery stores or pharmacies. The 180-degree shift is probably best exemplified by the U.S. Surgeon General’s swing from tweeting “Seriously people – STOP BUYING MASKS!” all caps exclamation point, to being featured in a video weeks later demonstrating how to improvise masks out of a bandana and rubber bands. The CDC has easy no-sew instructions at bit.ly/CDCDIY.

In addition to those who are sick and necessarily exposed to others, surgical masks are advised when disinfecting a residence that may have been exposed to the virus. You should also wear disposable gloves, open all of the windows while mopping the floor and cleaning all surfaces with a disinfectant solution, and wash all linens and the clothes you just wore cleaning with detergent. Make sure to hold soiled linens away from your body, and don’t shake them before they are washed. And, as always, take care to not touch your eyes, nose, and mouth when removing your mask, and carefully wash your hands afterwards. You can find all these instructions at https://bit.ly/COVIDcleaning.

“The suggestion that the public should not wear masks because healthcare workers need them more is [definitely] valid up to a point, but it is surely an argument for manufacturing more masks, not for denying them to populations who could potentially benefit from them. Until such masks are available in sufficient numbers, frequently washed cloth masks are recommended by the CDC.” I’ll talk about what are the best materials to use for them, as well as the role of N95 respirators, next.

In our next story – we look beyond that fashionable cloth face covering your aunt made you – to determine if it actually works.

Cloth face coverings are no substitute for actual masks but may be better than nothing. Let me show you a few studies. This study testing the efficacy of various homemade masks found that scarves, pillowcases, and 100 percent cotton t-shirts were probably the most suitable household materials, blocking various bacteria and viruses about 60 percent as well as surgical masks. As you can see, the average filtration efficiency was about 90% or more with surgical masks, compared to more like 50, 60, or 70 percent for the improvised fabrics. Vacuum cleaner bags worked better, right up there alongside surgical masks, but were considerably harder to breathe through, “rendering it unsuitable for a face mask.” The same with the tea towel.

Engineers at the University of Cambridge looked at 20 different options, compared to surgical masks. So, you can see, for example, that lightweight T-shirts have less than half the filtration of heavyweight cotton tees. As you can see, windbreakers and denim jeans are right up there, comparable to surgical masks, alongside the vacuum cleaner bags, but suffer the same problem. They’re “very difficult to breathe through…and are thus ill-suited for face mask construction.” Taking that balance between breathing and filtration into account, the most suitable fabrics for face mask construction may include something like cotton flannel, though in a pinch a single sock pressed tight against the nose and mouth might make a good emergency mask substitute. Regardless of which you use, try not to touch the front of mask while you’re wearing it or when you remove it, then wash your hands. And cloth face coverings should be washed regularly.

Even though face coverings are intended to protect others from the wearer rather than the wearer from others, masks were recommended for self-protection during the last pandemic for those at high risk in unavoidably crowded settings. In hospital settings, for example, mask wearers appeared to have been comparatively protected from contracting SARS. However, even three or four layers of cloth (in the form of cotton handkerchiefs) only filter a fraction of what a simple surgical mask can block. These are penetration numbers; so, four layers of cotton may only block 4%, 10 times less than a simple surgical mask.

Improvised masks didn’t seem to help in 1918, attributed to the fact that to get the necessary protective filtration, so many layers of gauze had to be used that breathing was difficult and air leaked around the edges. An improvised face mask should be viewed as the last possible alternative if a supply of commercial face masks is not available.

The World Health Organization still doesn’t think routine mask-wearing in public is necessary, expressing concern that it might lead to a false sense of security and neglect of more important measures such as hand hygiene and social distancing, and may lead to touching one’s face. On the other hand, one could imagine how wearing a mask might prompt people to avoid touching their face. Gloves could play a similar role. Seeing bright purple gloves on your hands can serve as a constant reminder. Here’s me recording the audiobook to How to Survive a Pandemic. Yes, you can still breathe in virus while wearing a mask, and you can still contaminate yourself with gloved fingers, but anything that keeps you constantly conscious about the position of your hands and stops you from touching your face might help.

Speaking of self-conscious, if everyone wore masks in public, symptomatic patients who definitely should be wearing them wouldn’t fear being singled out for stigma. Of course, universal use of face masks in public during a pandemic could only be considered if supplies permit. Sadly, inadequate preparation, misuse, and hoarding have led to a critical shortage of personal protective gear for those on the front line. That’s why the CDC is recommending “cloth face coverings” instead of surgical masks.

You know things are getting desperate when an editorial in the Journal of the American Medical Association entitled “Sourcing Personal Protective Equipment During the COVID-19 Pandemic” includes as a proposed suggestion … “coffee filter masks.”

Surgical masks are usually made out of paper with a gelatinous layer and should be changed every four hours or when they become wet with saliva or other fluid, whichever comes first. Surgical masks, as the name implies, are typically meant to protect others (as in the patient opened up on the operating table). N95 masks, or N95 “respirators” as they’re often called, are the cup-like masks that fit tighter to the face. They are intended to protect the wearer. The WHO and CDC have conflicting guidelines as to what healthcare workers should wear during routine care of patients with COVID-19. The CDC, along with its European counterpart, recommends N95 respirators, whereas the WHO suggests surgical masks are sufficient. While part of the WHO’s reluctance to endorse N95s may be out of a sensitivity to the global scarcity of such resources, the underlying transmission dynamics of the COVID-19 virus remain largely unknown; so, it’s impossible at this time to say which recommendation is right with any certainty.

The relative importance of direct respiratory spread for COVID-19 versus indirect contact via contaminated objects is unclear. For other viral respiratory illnesses like the common cold, breathing appears more important than touching. That’s what that arm brace study showed. For example, in one rhinovirus experiment, only 50 percent of those touching contaminated coffee cup handles became infected. For the flu, the relative importance of transmission continues to be debated, which is remarkable since we’ve known about the virus for nearly a century.

Note that N95 respirators only work at peak efficiency if they conform completely to the face; so, they aren’t for everyone. Even one to two days of stubble may significantly undermine the necessary seal. This is an actual infographic from the CDC showing which types of facial hair may or may not be suitable.

They also must be used properly. In a laboratory setting, N95 respirators have been found to be very effective, but out in the real world, a review of the best science on preventing the spread of respiratory viruses found “no evidence that the more expensive, irritating, and uncomfortable N95 respirators were superior to simple surgical masks.” Not that N95s aren’t better at filtration, but perhaps this result was due to poor compliance. I remember how uncomfortable they were when I was working with tuberculosis patients. So, that would support the WHO recommendation that N95s aren’t necessarily better in real world settings, though with proper fitting and compliance, they’d presumably come out on top.

Even with the perfect mask sealed over your mouth and nose, your eyes are still exposed, leading to a suggestion that medical workers wear goggles. Monkeys can apparently be infected by dripping the COVID-19 virus into their eyes, but a retrospective study of SARS, at least, found no documented cases of transmission to healthcare workers just because they didn’t use eye protection.

Until we know more about the transmission of this virus, it would seem prudent for those in close contact with coughing patients to err on the side of caution and use both eye protection (like at least a face shield) and N95 respirators. During the SARS outbreak in North America, regular surgical masks were initially recommended, but the advice switched to respirators after doctors started dying.

Here’s how N95 masks compare to various cloth face coverings. Note these are graphs of penetration, so you can see for an N95 mask there’s less than 5% penetration. So, at the particle size at which an N95 mask blocks more than 95%, a mask made out of a t-shirt blocks only about 10%, scarves about 20%, sweatshirts about 30%, and towels closer to 40%.      

It’s interesting that the Hanes t-shirts are no better than any of the other t-shirts, but the Hanes sweatshirts appeared to have an edge for some reason. Of course, the study was funded by Hanes—just kidding.