Blog #2: Keep your droplets to yourself
Hello! Hi! Welcome (back, if you read my previous blog)!
Today I want to talk about about the current COVID-19 pandemic, and specifically how YOU play a role in controlling it.
In the very likely event I start rambling in this post, I want to make sure that the main takeaway is clear from the very beginning.
Wear a mask.
I also want to preface this blog by saying I am NOT an expert on infectious diseases (not even close!). Reading about COVID-19 has become a slight interest of mine aka it’s how I’ve been spending a decent chunk of my research time, instead of doing my ACTUAL thesis research, during this time of worldwide crisis/pandemic.
Okay, let’s jump in by going over some names/terminology.
Coronavirus: a classification/type of virus. There are actually hundreds of kinds of coronaviruses that exist in other species, but only 7 have been found to infect humans. Of those 7, four cause the common cold. So, usually, (statistically, most) coronaviruses aren’t too scary.
SARS-CoV-2: the Novel Coronavirus – the newest strain of coronavirus that has infected millions around the world (at time of writing – Johns Hopkins has it tallied at 10,842,615 worldwide). In the early 2000’s, a similarly structured coronavirus caused a Severe Acute Respiratory Syndrome (SARS) epidemic. Since the Novel Coronavirus has a similar (but not identical!) structure, they have classified this as a SARS-like coronavirus. The “-2” here in the Novel Coronavirus nomenclature is just to signify that this is indeed a different virus strain than the 2000’s SARS coronavirus. SARS-CoV-2 is sometimes referred to as “Miss ‘Rona” in memes, or as the “Chinese virus” by racists.
COVID-19: COronaVIrus Disease-2019. This is the disease that is caused by SARS-CoV-2, discovered in late 2019. The virus often leads to mild respiratory infection; though sometimes can vary between no symptoms at all (asymptomatic) to severe infection requiring external oxygen supply, or even intubation to a mechanical respirator. Older populations (~60+), and populations with pre-existing health conditions (including heart disease, diabetes, chronic lung diseases), are more likely to develop severe cases of COVID-19 (requiring hospitalization), though severe cases have also been cited in otherwise seemingly healthy people.
At this current point in time, there is no cure for COVID-19. The only way to recover from COVID-19 is to give your immune system the chance to make antibodies that will fight it off for you. This means that people with preexisting conditions, that may have weaker immune systems, may not be able to fight off the virus on his/her/their own and may ultimately succumb to the virus.
And, there is currently no vaccine for SARS-CoV-2, meaning that we can’t reliably or safely give our immune systems a way to learn how to fight the virus before we are even exposed to it, thus putting us at a disadvantage if and when we are exposed to the virus.
Our best defense against the spread of COVID-19 is a mixture of a few things:
1. Physical distancing (i.e. avoiding large crowds; avoiding contact with those who you don’t live with)
2. Good hygiene (wash your hands with soap and warm water for >20s, frequently, or use a hand sanitizer when soap and water are not available; refrain from touching your eyes/nose/mouth/face, especially if you have not just washed your hands), and
3.Wearing a mask, when physical distancing cannot be totally enforced (i.e. at the food store).
In today’s blog I hope to explain why these methods for virus containment (really, just wearing a mask) are so important, starting with explaining a bit how the SARS-CoV-2 virus spreads. If you’re interested in reading more about mask-wearing, I’ve linked to some studies throughout, but also check out this comprehensive review article **which is pre-print and has not been peer reviewed yet** on the topic!
It has been fairly well established that SARS-CoV-2 can spread from an infected person through their respiratory droplets, basically small drops of liquid that expel from your nose and mouth when you breathe, talk, sing, shout, sneeze, or cough. If a person is infected with the SARS-CoV-2 he/she/they will likely spread the virus through these actions, if proper precautions aren’t taken. Ideally, the infected person should be physically isolated in order to avoid transmitting the virus to others. The current recommendation is at least 6 feet of space, for short durations of time and in a well ventilated area (i.e. outdoors, not a bar or restaurant).
However, with this virus, we see that some people have pretty mild symptoms (so mild they might not even realize they are sick), or have no symptoms at all, which is referred to as asymptomatic. It’s also possible that a person has contracted the virus and can spread the virus, before the symptoms have time to present themselves, which is referred to as presymptomatic. One of the many unsettling things about this coronavirus is that it is possible for asymptomatic and presymptomatic people to spread the virus, without knowing that they are sick.
Now, these asymptomatic and presymptomatic people are walking around, feeling good, living life, celebrating Independence Day weekend with a party with neighbors or friends or family. Maskless. Spewing their respiratory droplets all up in the business of fellow party goers. Next thing you know, 2-14 days (median =5.1, source) days later, many other party goers start to feel sick. If only there was something that could have prevented this! There IS, actually! TWO things! A. STAY HOME – don’t even go to the party in the first place! Facetime/Zoom parties are better anyway bc you can wear your pajama pants and no one judges you! B. WEAR A MASK – you can think of this as source control, as the respiratory droplets from carriers of the virus (symptomatic, presymptomatic and asmptomatic alike) are the source of transmission to uninfected people.
Since staying home 24/7 is basically impossible (many people still must go to work, we need shop for groceries, etc), let’s focus on option B.
The Center for Disease Control and Prevention (CDC) has stated the following: “simple cloth coverings slow the spread of the virus and help people who may have the virus and not know it from transmitting it to others.” (source: the Congressional hearings on COVID-19 transmission earlier this week). Let’s dig deeper into the science behind this!
What happens to the respiratory droplets that we breathe out when we’re not wearing a mask? Usually, they linger in the air for a bit, then eventually fall to the ground. More specifically, in a study published in May by Stadnytskyi et al at NIH and UPenn (supplemental data here), we find that the duration that the droplets linger in the air depends on the size of the droplet: the larger the droplet, the faster it falls (by Stokes’ Law – I cannot believe this came back into my life after years of not thinking about fluid dynamics lol). So, you breathe out droplets and gradually fall down. But, as they’re gently falling/suspended in the air, the water in the droplet evaporates (the rate of which depends on a few things, including the make-up of the saliva, and how many electrolytes are in it, as well as the humidity of the air – water will evaporate faster in dry air). As it evaporates, the droplet becomes lighter and will fall at a slower rate, so now the droplet will hang out in the air for even longer now! Also, the droplet won’t fall straight down to the ground just outside the mouth/nose – instead it will travel away from the person at a speed dependent on the size of the droplet and flow/force of the exhale (hello, conservation of momentum!). With this considered, 6 feet apart is believed to be a safe distance and lowers the risk of transmission (but does not totally eliminate!) between two people, theoretically for people with no masks, but ideally, wearing a mask lowers the risk even more - and here’s why!
There aren’t many studies – at least, not many that I could find - that have specifically looked at the role of masks in curbing the spread of SARS-CoV-2. However, there have been studies that have looked at how masks affect the number of droplets expressed with talking/breathing/etc. And since we know that SARS-CoV-2 is spread through droplets, we can use this as a proxy until more research is done, for now! A study published in the New England Journal of Medicine this past April 2020 by Anfinrudt P., et al., of the NIH showed that masks work in reducing droplets emission! The study used a laser box setup (lasers!! science is cool, guys!!) to count how many droplets were expelled as a subject repeatedly said “stay healthy”. The droplets ranged in size from 20-500 micrometers (think on the scale of ~ 1/10th the thickness of a fingernail), and the number of droplets, as indicated by “flashes” of light captured as droplets are illuminated by the laser, was higher as the subject reached the “th” sound in “healthy” (an interesting factoid for our linguists out there, maybe!). Also, more droplets were counted with louder speech — reaching a maximum of almost 350 flashes of light – meaning that we can release more droplets with shouting, laughing, or singing, as opposed to a whisper or even just breathing. Most importantly, when a damp cloth was placed over the subject’s mouth, the droplet count dropped to practically the same as background level with a mean number of flashes (proportional to droplet release) of 0.1 over the 1,000 frames! So, to limit release of our respiratory droplets into the surrounding environment, we can wear a cloth covering over our mouths and noses! This is especially important with SARS-CoV-2 transmission because even though we are feeling well and healthy, this doesn’t mean we are not infected and not spreading the virus. To make sure we don’t get anyone else sick, we want to keep our droplets to ourselves!
Another issue people have expressed concern about is the type of mask to wear (i.e. surgical mask vs. homemade cloth masks). Ultimately, surgical masks have been found to be more effective at blocking droplets than homemade masks, but homemade masks are significantly more effective than no mask at all (source and source)! Wearing a cloth mask might not guarantee 100% - or 75% - blockage of aerosols, but the belief is that by wearing a mask, you can lower the total amount of virus that is expelled into the air, which substantially decreases the risk of someone around catching the virus (through contact with eyes/nose/mouth) by decreasing the viral load that they are exposed to.
Now you may know people who – or you yourself! – might be hesitant, resistant even, when it comes to wearing a mask out and about. It’s impeding on our normal breathing! It’s uncomfortable! It’s SUMMER and the air is humid and its hard to breathe! It will give me weird tan lines! These are all true statements. I hear you. I get it. But actually, most masks are made with these concerns in mind (well, maybe not the tan lines one, but hopefully we can deal with that for now)! The filters in face masks allow suuuuuper small paricles like oxygen (O2), which is ~300 picometers or ~0.3 nanometers in diameter, to easily diffuse through, but bigger particles (like respiratory droplets, which can be as small as 5-10 micrometers in diameter – at least 10,000 times larger than O2 – or droplets from speech which can be slightly smaller at around 1 micron – but that’s still 3,000 times larger than O2!), cannot pass through. These masks are designed to not suffocate you. The engineers who design and make and test and retest the masks make sure that the mask they create specifically will NOT cut off your oxygen supply (that would kind of defeat the purpose, after all!). Even most cloth masks that I’ve seen have filtration efficiencies ~300 nm range, still 100x larger than the size needed for O2 to pass. When wearing a mask, you may feel short of breath, but it’s possible the mask either 1. is too tight – it should be snug around the cheeks and under the chin, but not constricting, 2. is not made out of the recommended material (cotton should be fine), or 3. is causing anxiety that makes it harder to breathe – this happens to me a lot when I’m wearing a mask, honestly. Before we write it off and refuse to use the mask, let’s make sure we’re doing everything in our control to make sure we are doing it correctly, and with an open mind!
Also, if you’re more of a visual learner, check out this Twitter thread Dr. Rich Davis shared about wearing masks. He shows that when wearing a mask, things like sneezing, singing, and coughing lead to less bacterial spread/contamination (this is just bacterial spread, including the good/not harmful bacteria we have naturally occurring. It’s not necessarily SARS-CoV-2 spread, but you get the idea!).
But, here’s the thing – and it’s a BIG thing – wearing a mask to stop the spread only works if compliance is high. That is, if EVERYONE wears a mask, we can not only dramatically reduce community transmission of the virus, but also reduce the clinical, financial, emotional burdens that the pandemic has put on us as a nation (and the world!). So, it’s up to YOU. And ME. And CHRIS EVANS. And every person (over the age of 2 :]) in the country. To wear a mask and stop the spread.
In closing, I want to talk a bit of philosophy. And by talk, I mean ramble for two more paragraphs.
Some people argue that, since there is no evidence or clinical trials that PROVE the effectiveness of masks for SARS-CoV-2 transmission, we should default to the opinion that masks are INEFFECTIVE and we shouldn’t bother wearing them. This thought process makes me think of the Renaissance philosopher (and scientist/mathematician!) Blaise Pascal I learned about in AP European History in 10th grade. The philosophy went like this: While we live, we have two options: we can believe in God, or we can not believe in God. And, when we die there are two possible outcomes: one is that God is real, and the other is that there is no God. If we DO believe in God and there IS a God, we’re rewarded by going to Heaven when we die, enjoying an eternal bliss (BEST case scenario). If we DON’T believe in God and there IS a God, we go to Hell, suffering an eternal punishment (WORST case scenario). If we DON’T believe in God and there ISN’T a God, well, nothing matters because when we die, we die, and there’s nothing after that (a meh-case scenario). But, if we DO believe in God and there ISN’T God, then we don’t get an eternal anything, when we die, we die; but the argument is that, you had good intentions in your life by hoping for the best outcome, and at least you have the comfort of faith during your mortal life (a maybe slightly better than meh-case scenario). So, Pascal argues, believe in God, because the potential outcomes are better.
Let’s think about this in terms of masks, and whether masks actually protect against the virus or not (even though now we know they definitely don’t not help :]). We have two choices: we wear a mask, or we don’t wear a mask. And, we have two outcomes: masks work to limit the spread of SARS-CoV-2, or masks do not work. Now, if we wear a mask, and masks do work, then we can LITERALLY SAVE LIVES if we are an asymptomatic or pre-symptomatic carrier. We might be shedding the virus, but our masks are containing a majority of our respiratory droplets, so we are lessening the viral load exposed to other people (BEST case scenario - Yay!). If we don’t wear a mask as a possible a- or pre-symptomatic carrier, and masks do work, then we are potentially infecting other people, causing someone else’s potentially life-threatening illness when it could have been avoided (WORST case scenario). If we wear a mask, and masks don’t end up being an effective way to prevent the spread, then, well, we had good intentions, we tried the best we could and wore an extra piece of fabric for a little while, but still might end up infecting others, A for effort (a meh-case scenario). If we don’t wear a mask and masks don’t work, then we’ll end up infecting others with the intentions/implications of “we’re all going to get sick anyway/it’s inevitable/even if there was something I could have maybe done to prevent my giving you the virus, I didn’t do it, F for effort (a less-than-meh-case scenario, in my opinion). So, I’m (and many public health experts are) arguing, wear the mask because the potential outcomes are better.
(Sorry that might have been kind of a strange analogy. I’m not trying to tell you whether you should follow a religion or not. I don’t really care what you do. As long as you wear a mask. :] ).
In closing, wear your mask while grocery shopping, while chatting with neighbors from a safe distance, while walking or visiting public settings. It’s the easiest way to save lives.
Please wear yours to protect me. I’ll be wearing mine to protect you.
Be safe. Be smart. Be kind.
Talk to you next time,
-s
