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Linsey Marr Profile picture
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4 Oct, 4 tweets, 3 min read
We did some more testing yesterday and updated tinyurl.com/VTkidsmasks with a column dedicated to efficiency as worn. Added results for KF94/KN95s received from @masknerd. Take homes: N95 clearly the best (small 3M Vflex 9105S), KF94/KN95s around 90%, most cloth masks ~60-80%. /1
@masknerd Cloth masks with filter are widely available. Most important is good fit and minimal leaks, which is easier to get with softer, more flexible fabrics, as we also found in @isjinpan's study on manikins. tandfonline.com/doi/abs/10.108…, free preprint at drive.google.com/file/d/1PoE0gk… /2
Based on our testing and some new studies, we moved all cloth masks to the BETTER category and moved surgical + brace or surgical + cloth double masking to the BEST category, which also has KN95/KF94 (small-sized N95s may work for big kids). /3
On second thought, I shifted the surgical options to the BETTER category, based on results shown here: HT @RolandSB13 /4

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More from @linseymarr

Linsey Marr Profile picture
11 Aug
Our new preprint led by Hawks and Duggal shows infectious virus emitted in air from hamsters (upper right) on days 1-2 but not later, even though RNA still there (lower right).
biorxiv.org/content/10.110… /1
We used a condensation particle sampler with & without cyclone. Saw similar amounts of infectious virus, so it's mostly <8 μm.

8-μm particles can float around for at least 13 minutes, and the smaller ones stay in the air for hours. /2
Sampling method does not exclude potential for resuspension from fur and ground, but there was more virus in oral swab & nasal wash than on fur. Either way, though, there's infectious virus in the air. /3
Read 4 tweets
Linsey Marr Profile picture
6 Jul
How to keep a gym open more safely during a pandemic. We kept doors open and increased ventilation from 7 liters per sec per person to 240 L/s/p. ASHRAE recommends 10 L/s/p. wwwnc.cdc.gov/eid/article/27… /1
An infected trainer exposed 50 clients, but there was no apparent transmission. Enhanced ventilation probably helped. Also had reduced occupancy, >10' distancing, hygiene, but no masks. /2
Stories in media from last fall: cnn.com/2020/11/19/us/…, wsj.com/articles/gym-r…, insider.com/how-gym-preven… /3
Read 4 tweets
Linsey Marr Profile picture
1 Jul
Real-world test of ionization in a campus building. We did not see a reduction in particle number concentrations at supply vent when system was on vs. off, measured using TSI Aerotrak. /1
Thanks to @VTFacilities for suggesting this and providing access. Photo shows the ionization unit in blue inside the HVAC duct. /2
@ajprussin and David Kormos took turns holding the particle counter at the supply vent. /3
Read 6 tweets
Linsey Marr Profile picture
18 Jun
Latest from our lab @jinpan et al. onlinelibrary.wiley.com/doi/full/10.11… Why are seasonal patterns of flu & other viruses different in temperate (more in winter) vs. tropical (sporadic, maybe with rainy periods) regions? Indoor climate may be a driver. /1
But most studies look at disease incidence vs. outdoor weather; outdoor data more readily available. Need to understand relationship between indoor & outdoor climate to better interpret results. /2
Indoor temp usually 20-30 C everywhere, but humidity varies widely seasonally (very low in winter in temperate regions) and is higher in tropics. Indoor relative & abs humidity usually well-correlated with outdoor AH, except with heavy A/C use. /3
Read 4 tweets
Linsey Marr Profile picture
1 Jun
Why the big debate over airborne transmission? Exchanges with @OlabisiLab Matthew Meselson @kprather88 over the weekend helped me crystallize some thoughts about the disconnect. /1
Traditional discussion about transmission routes centers around operational definitions in infection control and prevention in hospitals. There are "airborne" diseases/precautions and "droplet" diseases/precautions. /2
The problem is that we have been trying to impose these operational definitions on the actual mechanisms of transmission and apply them in community (non-hospital) settings. /3
Read 13 tweets
Linsey Marr Profile picture
7 May
Deep dive by @zeynep from a sociological perspective on what we who have studied airborne transmission for a while, have been observing. nytimes.com/2021/05/07/opi… /1
There is a paradigm shift taking place, to correct misunderstanding in how respiratory infections are actually transmitted. /2
Traditional understanding of transmission routes was defined mainly by epidemiological observations--who gets sick when and where--and relied on being able to envision viruses moving between people in large droplets or on objects (fomites). /3
Read 6 tweets

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