Corona Roundup: Masks and Google Searches

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This past week, the recommendation was made for everyone to consider using the use of cloth face masks. In addition, a new idea has popped up that Google searches can predict the spread of the disease. That last one may teach us quite a bit about how to identify COVID-19 early. Let’s dig in.

Everyone Wearing Masks?

After the CDC saying that only sick people should be wearing masks, the organization did an about-face this past week and recommended more widespread mask use:

“CDC recommends 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.”

So does this make any scientific sense? Is there new data that shows that this slows the spread of the coronavirus or is this just a move to make us feel good?

The Science?

First, let’s discuss what we’re really talking about here. Not N-95 respirators nor surgical masks, but masks made by people at home using a sewing machine, scarves, or a t-shirt.

The National Institute for Occupational Safety and Health (NIOSH) performed a study on using clothing such as sweatshirts, t-shirts, and scarfs in healthcare settings (1). The conclusion? That these items could provide only marginal protection against small particles. These are the ones that everyone is so concerned about carrying the virus and hanging in the air.

However, maybe NIOSH is wrong? Is there a clinical study? A randomized controlled trial compared the ability of surgical and cloth masks to prevent healthcare workers from contracting the flu. It found that workers wearing cloth masks were thirteen times more likely to get a respiratory viral infection than those workers wearing medical masks (2).

Some New Research?

A new study was just published in the journal Nature using surgical face masks and patients who had diagnosed respiratory viral infections (NOT the novel coronavirus) (5). The goal here was to see how much viral transmission the masks stopped during actual coughs. The good news is that under real-world conditions, the surgical masks seemed to stop most of the smaller particles (the droplets in this study, at under 5 microns, were bigger than the super small ones everyone is concerned about).

The Common Sense Part

The size of the pores or opening in a high-quality t-shirt are 0.85 mm (30 thread count per inch). Let’s decrease that by 1/3, meaning we’re now using very high-quality fabric at 100 thread count, so the pore size is 0.28 mm or 280 microns. How big are the small cough particles we’re discussing here? They’re less than 1 micron or smaller (3).

So what does that look like?

do cloth masks work for coronavirus

Here I made the small droplet big enough so we can see it, as to scale it would be a tiny period sized thing.

It would take a thread count at >1,000 to start to stop these droplets. You could try tripling or quadrupling up on 300 thread count fabric, which may work just a little. Surgical masks will stop 20-70% of these small droplets depending on how fast the droplet is moving and how the mask is made (4). In fact, only HEPA filters have pore sizes small enough at 0.3 microns, to stop or filter these small water droplets from coughs.

Hence, in conclusion, the idea that cloth masks will stop the spread of the most problematic small droplets is not founded in any science. This is just a move to keep the natives happy and complacent.

Google Searches that Teach Us About the Virus

There was a really interesting opinion piece by a data scientist diving deep into the type of Google searches being done on COVID-19 symptoms and the extent of the outbreak in that part of the world (6). One of the first symptoms of COVID-19 is the loss of the ability to smell. That google search (“I can’t smell”) correlates reasonably well with U.S. cases confirmed state by state. This idea of using Google searches to track disease outbreaks is not new and has been studied before.

I overlaid the day by day COVID-19 case data from Italy on top of the Italian search data on the loss of smell here (one lags the other by several days as losing the sense of smell is an early symptom):

italian searches for loss smell and cases

You can see some fit of the two lines around the double peak in the middle and less at the end of March (this graph is through April 1). Did the Italians recently up their testing capability to ID more cases? That could explain the divergent lines at the end of the graph.

An interesting take-home from this article was that one of the searches that correlated the best with COVID-19 was “my eyes hurt”. So is this a common symptom?

The upshot? Wearing a scarf or t-shirt or even a properly sewn cloth mask is unlikely to do little to protect you or anyone else. However, it may make you or someone else take social distancing more seriously, which may be why we’ve been asked to do this. In the meantime, Google searches could be a reasonable way to track the disease spread without widespread blood tests. Maybe we’ll see a world where big data identifies micro-hot spots in neighborhoods based on Internet searches and then we focus widespread blood testing in these areas?



(1) Rengasamy S, Eimer B, Shaffer RE. Simple respiratory protection—evaluation of the filtration performance of cloth masks and common fabric materials against 20-1000 nm size particles. Ann Occup Hyg 2010 Jun 28;54(7):789-98

(2) MacIntyre CR, Seale H, Dung TC, et al. A cluster randomised trial of cloth masks compared with medical masks in healthcare workers.BMJ Open 2015 Apr 22;5(4):e006577

(3) Zayas, G., Chiang, M.C., Wong, E. et al. Cough aerosol in healthy participants: fundamental knowledge to optimize droplet-spread infectious respiratory disease management. BMC Pulm Med 12, 11 (2012).

(4) Chen CC , Willeke K. Aerosol penetration through surgical masks. Am J Infect Control. 1992 Aug;20(4):177-84.

(5) Leung, N.H.L., Chu, D.K.W., Shiu, E.Y.C. et al. Respiratory virus shedding in exhaled breath and efficacy of face masks. Nat Med (2020).

(6) Stephens-Davidowitz S. New York Times. Accessed 4/6/20.

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10 thoughts on “Corona Roundup: Masks and Google Searches

  1. Bob McClure

    Wearing a mask also keeps you from touching your face, so it acts as a shield rather than a filter. It is the virus on your hands from touching a contaminated surface, then your face (self infection), that we also need to defend from. Your thoughts?

    1. Chris Centeno, MD Post author

      I think it might be a bit helpful there, but given that clinical trials at U of M showed that this didn’t really work to stop the spread of the flu, my guess is that’s likely not a valid mechanism to slow the spread. It may be a way to get more people to take this all more seriously.

  2. Terry

    I commend you, Dr Centeno, for your always incisive & factual analyses. We all know Trump’s ‘task force’ has spread a lot of very bad info [regretably, Dr Brix & Dr Fauci have enabled some of that]. Re masks: Do you agree that it was stupid for feds to order ‘N95’ masks to be used by our frontline Drs & nurses, when in fact, N or P99 or N/P100 masks would give even more protection? N95 masks under the best of circumstances will only filter 95% of the particles down to 0.3 micron size. WHY WOULD ANYONE WANT TO RISK EVEN 5% OF PARTICLES GETTING INTO THE LUNGS OF HEALTHCARE PROS? As you point out, the OSHA tested & rated masks only down to 0.3micron particles, NOT smaller virus sizes in the 0.1 micron size. So even IF N95 masks capture some 0.1 micron viruses, the N95 is still letting 5% of particles into the lungs of medical staff! And why “N”: such masks are NOT resistant to ‘oily mists’. Viruses may not be an ‘oily mist’, but they certainly may be moist–wouldn’t a “P” rated mask have been wiser to provide more protection for med personnel from moist droplets? It seems to me that the correct national priority would have been to order masks that gave the MAXimum possible respiratory protection to medical staff. After all, when they get ill or die, the Nation’s ‘frontliine’ defense against the epidemic is weakened. Of course the failure to order more protective masks for med staff use is only 1 of the many failures of Trump et al to take early & proper action. What I don’t understand though is WHY FAUCI & BRIX LET TRUMP ORDER N95 MASKS INSTEAD OF P99/P100 MASKS TO GIVE MEDICAL STAFF THE MOST PROTECTION POSSIBLE?

    1. Chris Centeno, MD Post author

      The issue is just water droplet size under 1 micron. Yes, I think the better rated masks might be better, but you also need to realize that comfort and the ability to move air may be the rate-limited factor for healthcare workers.

  3. Frank Romeo

    Pore size is not the only criteria in effectiveness of a mask. Particle velocity, and particle path can be very important, the adhesion properties of the material and the droplet and the use of antiviral coatings. I’m not a doctor but an engineer, multiple layers of fabric are effective in stopping water borne particles. Antiviral coatings are available for cloth. Unless a single viral bit is all that is necessary to cause an infection multiple layers of material can be an effective barrier. Just as in your double blind testing is required for medicine, real tests are required to test the effectiveness of material masks.

    1. Chris Centeno, MD Post author

      Those clinical studies have been done, please see the post. Yes, all of these things matter, see

  4. Stuart Bell

    Kinsa,, has a good argument that temperature is a good predictor of coronavirus density. They lead CDC reported cases by about 2 weeks.

  5. D Page

    The surgical masks we use are rated at 95.5% bacterial filtration efficiency (BFE) and 99.7 particular filtration efficiency (PFE) @ 0.1 micron. A quick check on the corona virus size shows 125 nano meter diameters (0.125 microns), so although far from perfect their use makes much more sense than NOT using them. Additionally, due to the risk of infiltration at the four edges of the mask we tape the mask to the face around the mask circumference at all four edges of the mask to help reduce the infiltration around the edges of the mask/face interface. And since the particle sizes are likely larger than the individual virus diameters due to virus in aquas solution, an even better retention is likely.
    The use of a very fine mist of colloidal silver onto the mask, face, eyes, nose and mouth after leaving an where exposure to people occurred, may further thwart any retained virus particles in the mask or the face area.

    1. Chris Centeno, MD Post author

      Yes, the issue is the mask fit, so taping makes sense.

  6. Doug Husovsky

    If the mask captures any particulate matter then you will be exposed to these trapped particulates for a longer duration of time than if you walk past a ‘cloud’ type of event how can this possibly help? Since they can pass through the material can they not just as easily break away? Should we change our shirts to and our pants when we get home as well as toss the mask in the wash? What about those with hair? Doe it trap the virus as well? Where does it end should we burn everything when we get home?

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