Our multidisciplinary team sought to correct some bits of conventional wisdom on transmission of viruses through the air. Still working with historian @ethomasewing and others to show how these bits became embedded. journalofhospitalinfection.com/article/S0195-… Myths... /1
Myth 1: “Aerosols are droplets with a diameter of 5 μm or less”

Myth 2: “All particles larger than 5 μm fall within 1-2 m of the source”

Myth 3: “If it's short range [close contact], then it can't be airborne”

Myth 4: “If the basic reproductive number, R0, isn't as large as for measles, then it can't be airborne”

Myth 5a. “If it's airborne then surgical masks (or cloth face coverings) won’t work”

Myth 5b: “The virus is only 100 nm (0.1 μm) in size so filters and masks won't work”

Myth 6: “Unless it grows in tissue culture, it's not infectious”

Thanks to the fearless Stephanie Dancer and Julian Tang for leading this. HT @HuffmanLabDU @PrasadKasibhat1


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More from @linseymarr

27 Dec 20
A 🧵on humidity and airborne viruses. Several articles have said that at higher relative humidity (RH), droplets/aerosols retain more water, are larger, and then fall out of the air faster. True, but the effect of RH on biological decay is probably more important. /1
.@DrWanYang and I studied this question in 2011, exploring different removal mechanisms from air as a function of RH. I thought we’d find that at high RH, droplets/aerosols would be a lot larger and settle out quickly. journals.plos.org/plosone/articl… /2
But the biological inactivation rate is more sensitive to humidity. See bigger steps in RH for inactivation than for settling in Fig. 5. We used decay rates for influenza from Harper 1961. Also note the difference ventilation makes at 1 vs. 10 ACH. /3
Read 13 tweets
14 Dec 20
Absolute 🔥 from the inimitable @edyong209! So much insight, so succinctly written, with input from scientists with deep expertise (from well before 2020) on viruses. Excerpts with my thoughts follow... /1
Their movements through the air have been poorly studied, too. “There’s this very entrenched idea,” says Linsey Marr at Virginia Tech, that viruses mostly spread through droplets (short-range globs of snot and spit)... /2
rather than aerosols (smaller, dustlike flecks that travel farther). That idea dates back to the 1930s, when scientists were upending outdated notions that disease was caused by “bad air,” or miasma. /3
Read 8 tweets
23 Nov 20
We started studying cloth masks in March. Preprint now at medrxiv.org/content/10.110… Take-home: Cloth masks are not an N95, but they work reasonably well for aerosols 1-2 microns and larger, which is the size that we think mostly mediates transmission. See thread. /1
.@jinpan @charbeleharb & Leng tested vacuum bag, microfiber, coffee filter, MERV 12 filter, cotton, acrylic, bandana, CDC sewn & non-sewn designs, surgical mask, face shield for material filtration efficiency in a filter holder and inward and outward protection on a manikin /2
For submicron particles, vacuum bag, microfiber, and surgical mask filtered out >50% of aerosols. Other materials were way below 50%. /3
Read 6 tweets
5 Oct 20
CDC's new guidance is out: "COVID-19 can sometimes be spread by airborne transmission" cdc.gov/coronavirus/20… /1
"Some infections can be spread by exposure to virus in small droplets and particles that can linger in the air for minutes to hours. These viruses may be able to infect people who are further than 6 feet away from the person who is infected or after that person has left...." /2
"This kind of spread is referred to as airborne transmission and is an important way that infections like tuberculosis, measles, and chicken pox are spread." /3
Read 7 tweets
25 Jul 20
Nearly tears of joy seeing new paper in medical journal with correct analysis and interpretation of aerosol transmission: thelancet.com/journals/lanre… See thread for summary of main points. /1
Where we have been: "Current infection control policies are based on the premise that most respiratory infections are transmitted by large respiratory droplets—ie, larger than 5 μm— produced by coughing and sneezing, then deposited
onto exposed fomite or mucosal surfaces." /2
Pathogens (e.g., M. tuberculosis, influenza, RSV, rhinovirus, many more) are consistently found in small aerosols <5 microns and if size-resolved data available, in much higher amounts than you would expect based on aerosol or droplet volume. /2
Read 11 tweets
9 Jul 20
My thoughts on WHO's updates:
who.int/publications-d… is an improvement
who.int/news-room/q-a-… is still in denial. See thread below /1
WHO's updated scientific brief on transmission of COVID-19 is a step in the right direction because they now acknowledge that airborne transmission may be occurring outside of specialized medical procedures, although they remain fixated on medical procedures as... /1
the main source of aerosols when we know they are generated by normal respiratory activities such as breathing, talking, singing, laughing, etc. /2
Read 11 tweets

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