I've been getting asked the question about universal masking and have gathered my thoughts. See thread. /1
There are reasons to think that universal mask wearing will allow us to re-open the economy, with restrictions, without causing huge spikes in cases that will overwhelm hospitals. /2
These reasons include our understanding of how masks work, how COVID-19 spreads, and indications that other countries with widespread mask wearing have much lower rates of infection. /3
Agreed that other factors are also important in these other countries. There is no magic bullet. Thanks to @kprather88 for good discussion on the topic.
It is true that there are no studies that adequately replicate the conditions we're talking about--everyone wearing homemade masks with a virus that may or may not transmit more by droplets/aerosols compared to other viruses--so we don't know how big the effect will be. /4
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Lidia Morawska led this retrospective piece on our efforts to convince the WHO to recognize airborne transmission. I contributed to some of the recommendations: academic.oup.com/cid/article/76… /1
1. Multidisciplinary mechanisms should be created by which decision-makers should be accountable for using or rejecting science, in a transparent and timely manner.
/2
2. Decision makers should use the best available science and not contort the science in order to fit a decision that may hinge on multiple factors. /3
Particles were mostly C, some Na+P+K+Cl, heterogeneous. /2
We classified them (% of total particle number): ~52% carbonaceous, ~45% Na-rich salt, <1% P-rich or K-rich salt, ~2% mixed salt. Number ratio of Na-rich salt to carbonaceous particles increased with increasing particle size... /3
Fascinating video about the history of mask use since the time of the bubonic plague @NEJM. China's experience with Manchurian plague probably made mask wearing more acceptable there. Anti-mask sentiment in US during 1918 flu. nejm.org/doi/full/10.10… HT Julian Tang. My take... /1
Masks work vs. masks don't work. Both sides are right and both are wrong because masks are neither 100% nor 0% effective. It is certain that they reduce exposure to airborne pathogens, and this reduces the risk of transmission and infection. N95/KN95 > surgical > cloth. /2
Masks are one of many tools that we can use to protect public health. They have costs and benefits that society and individuals must weigh. /3
ASHRAE's Positions on Infectious Aerosols document just published at ashrae.org/file%20library…. Proud to have worked on this with committee of experts for >1 yr. Positions: /1
* Exposure to infectious aerosols is an important factor in the transmission of infections in indoor environments between a source and a susceptible individual. /2
* Engineering controls demonstrated to reduce the risk of exposure to infectious aerosols include dilution with outdoor air provided by mechanical or natural ventilation, filtration of indoor air, indoor airflow patterns, and... /3
“If you’re doing extra hand washing ... then you should also be wearing a good mask in crowded indoor environments,” Marr said. “If you’re bothering to clean the surfaces, then you should be bothering to clean the air.” /1
Article cites a fun study of rhinovirus transmission. Infected + susceptible men played poker. Some wore restraints and couldn't touch face. >50% became infected, presumably aerosols. Soggy cards were moved to different room with new susceptibles. 0 became infected... /2
It's clear to me that Ebola is NOT transmitted mainly through the airborne route, but there is a chance for aerosolization of virus-laden fluids (e.g., diarrhea). We evaluated this using surrogates in toilets, sewer, wastewater treatment. /1
"Transmission is not thought to occur via air, water, or food, although in theory, aerosolization of blood and body fluids has the potential to lead to infection, as aerosol transmission has been demonstrated in nonhuman primates." /2
"Besides inhalation of aerosolized virus, contact of unprotected mucous membranes such as the eyes and mouth with aerosolized virus is also a potential route of transmission." /3