Covid: the importance of masks, and ventilation
An article came out pretty recently documenting the importance of mask wearing in decreasing Covid for mask-wearers and those around them (see covid mask importance jama2021 in dropbox, or doi: 10.1001/jama.2021.1505)
Details:
-- it is clear that SARS-CoV-2 spreads largely through exhaled respiratory droplets smaller than 10 µm in diameter; these increase with the force of expiration (e.g. coughing, sneezing, singing, exercising, talking loudly), and that exposure increases with proximity to the respiratory droplet exhaler. And that these droplets linger with poor ventilation (leading to recommendations for mask wearing indoors)
-- 10 studies were reviewed for this article, documenting important large-scale benefit of mask wearing, without distinguishing the specifics of the type of masks used in the community
-- they note that in many of these studies mask wearing occurred when other mitigation strategies were in place prior to beginning the mask wearing
Results:
-- mask wearing improves source control (i.e. blocking exhalation of virus-containing droplets, thereby protecting others)
-- for example, in a hair salon, 2 symptomatic infected stylists took care of 139 clients (with close proximity) and none of the 67 who were subsequently interviewed and tested developed Covid infection (see Absence of Apparent Transmission of SARS-CoV-2 from Two Stylists After Exposure at a Hair Salon with a Universal Face Covering Policy - Springfield, Missouri, May 2020 - PubMed (nih.gov)
-- laboratory studies confirm that multilayer cloth masks were more effective than single layer masks, blocking 50 to 70% of exhaled droplets, and may approach the effectiveness of surgical or procedure masks
-- and, the data suggests that "the prevalence of mask use in the community may be of greater importance than the type of mask worn"
-- masks protect uninfected wearers, blocking larger respiratory droplets that could infect them when virus hits exposed mucous membranes of the eye, nose, and mouth; they can also filter out smaller droplets and particles from the inhaled air
-- for example, on the USS Theodore Roosevelt aircraft carrier, those who wore a mask had a 70% lower risk of testing positive for SARS-CoV-2, 55.8% versus 80.8%, though people did use other mitigation strategies including social distancing (see https://www.cdc.gov/mmwr/volumes/69/wr/mm6923e4.htm?s_cid=mm6923e4_w)
-- though this protective effect is clear from this and other studies, it seems to be at a lower protective effect than found in source control
-- Covid spread decreased in 15 states and the District of Columbia after mask mandates were in place, with the benefit increasing as more time elapsed
Commentary:
-- of course, the main reason I am reviewing this study, is the preponderance of fake news/fake science undercutting the importance of masks. This anti-science is likely a significant component leading to the current Covid surge in areas where high-ranking officials use their bully pulpits to undercut the importance of masks and the science documenting their effectiveness (e.g. in Florida and Texas, but other states as well). And this is also likely a component to the surge of Covid cases in schools e.g. see https://thehill.com/homenews/state-watch/570870-alabama-schools-report-13000-covid-19-cases-in-two-week-period , where there is no mask mandate, though many school districts are requiring mask wearing at this point. this report documents 13,532 Covid infections in Alabama schools in a 2-week period, where only 84 of 142 school district actually reported their data (ie, these numbers are actually likely very low, since my guess is that the school districts not reporting their numbers are more likely the ones less likely to encourage mask use....)
-- one profound reason for mask wearing in general with Covid is that a high percentage of people (probably more than 50%) are able to transmit the virus when they are asymptomatic or presymptomatic (ie half of the infected people are largely unaware they have the virus at a time of high transmissibility). And transmissibility is increased with the Delta variant...
-- for example, in these waning days of summer, we are all more likely to get other infections or allergies with mild symptoms, which we may well write-off as non-Covid and not take appropriate precautions/quarantine (eg see http://gmodestmedblogs.blogspot.com/2021/08/covid-delta-variant-from-infected.html , where an unvaccinated teacher who had a couple of days of "allergy symptoms" took off their mask and infected 50% of the exposed kids)
-- one concern that comes up is the uncomfortableness of the masks, especially in kids. People may have more difficulty discerning emotions when others wear masks (though there was a study in children aged 7 to 13 finding they were able to infer emotions accurately even when others wore masks). There may be some benefit here for clear masks (e.g. transparent surgical masks). And a small study found that there is no reduced oxygen saturation or carbon dioxide retention when wearing a mask, using a six-minute walk test in staff physicians and veterans with severe COPD (see Effect of Face Masks on Gas Exchange in Healthy Persons and Patients with Chronic Obstructive Pulmonary Disease | Annals of the American Thoracic Society (atsjournals.org)
-- The above data summary, given the likely wide array of different types of masks used as well as the likely inconsistent correctness of their use, suggests that just encouraging a person to wear a mask is an important goal, and that choosing the optimal mask is likely more protective but may also be a significant obstacle for people to wear masks regularly. I.e., the benefit of just using a mask on a larger public health scale may well outweigh the risks of not wearing a mask because of discomfort, difficulty/cost of procuring, etc.
--the CDC has an updated website of studies updating studies on mask wearing, see Science Brief: Community Use of Cloth Masks to Control the Spread of SARS-CoV-2 | CDC
Limitations:
-- it is hard to differentiate accurately the specific component of mask wearing from other additional mitigation strategies. And those more likely to wear masks are also likely to integrate other mitigation strategies into their lives
So, masks work. They do protect both the wearer and those around the wearer. And the shoot-yourself-in-the-foot strategy of many of our “leaders” is tantamount to second-degree murder (i.e., by not encouraging safe behavior, sort of like dismissing the role of seatbelts or bike/motorcycle helmets).
-- it is profoundly significant and pathetic that the current Covid surge has led to rationing care in hospitals in Idaho and perhaps soon in other states (see https://www.nbcnews.com/news/us-news/idaho-begins-rationing-health-care-covid-surge-crushes-hospitals-n1278670 . their governor has not imposed limits on gatherings and businesses are largely operating as normal, though the governor does lament that this is an "unwanted point in the history of our state" (ie, you don't always get what you want, but if you (actually) try some time, you might get what you need)
-- and, though there are crisis guidelines to guide the rationing decisions, i personally would not be so very surprised if there were inherent biases in the decisions at a local level, perhaps related to different access to care in poorer communities vs richer, or just inherent biases prevalent in the on-the-ground decision-makers valuing some lives over others (eg their own racial/ethnic/wealth/social status biases)...
-- though mask-wearing is certainly helpful, the bigger picture issue is still: vaccinate, vaccinate, vaccinate
-- and, in terms of shoot-yourself-in-the-foot strategies, perhaps it is also time to deal with the very large number of guns in homes, another perhaps more literal shoot-yourself-in-the-foot outcome...
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as an addendum, there was an article in NY Times of a preprint study assessing the role of the indoor environment in the spread of Covid (see https://assets.researchsquare.com/files/rs-861942/v1_covered.pdf?c=1630438371 for the article and https://www.nytimes.com/2021/09/05/health/covid-ventilation-college-dorm.html for the NY Times article/summary). in brief:
--35 students (17 male) at University of Oregon who were Covid-positive between January and March, moved to single rooms for 10-day quarantine
--researchers assessed several features of the room by PCR: air sampling (including bathroom exhaust), swabbing surfaces (eg, computer, phone, bathroom floors), sampling form students' noses and mouths for the 10 days of quarantine, finding:
--all of the samplings had decreasing viral loads over time, except in the bathroom floors, bathroom exhaust
--there was a relationship between the amount of virus (by the PCR cycle threshold) in the students' personal samplings and the amount of virus in the samplings in the room
--though there was lots of virus in the students' personal samplings, there was more if they were symptomatic (self-reported), especially if they had coughing or GI symptoms
--the mechanical ventilation rates were calculated using the students' self-reported assessment of how often the windows were open
--overall the most dramatic decrease in viral loads was for samples taken from the phone and computer, and with active air samples
--comparing viral loads in rooms with windows open to closed: the viral loads were twice as high in those in rooms that the window was closed more than half the time (these viral loads were all still pretty high, though the difference was impressive, especially given the pretty small differences in calculated air exchanges/hour)
--limitations: small study, we are relying on self-reports, and we do not know if the virus was viable at the different PCR samplings (which do pick up dead virus). also, they used the binary assessment of windows open >50% vs <50% of the time, instead of a more revealing measurement of air exchanges as a continuous variable
geoff
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