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Linsey Marr Profile picture
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6 Jul, 4 tweets, 2 min read
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
Thanks to Kyle T. Bernstein, John T. Brooks, and Velvet Minnick for their assistance with this investigation, that is now published as a comment letter in CDC's Emerging Infectious Diseases journal. /4

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More from @linseymarr

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
Linsey Marr Profile picture
29 Apr
1) Where did the 5-μm cutoff for aerosols in disease transmission come from? (It should really be ~100 μm)

2) Where did the 6' rule come from?

@katierandall @EThomasEwing @jljcolorado Bourouiba & I traced the history in this preprint papers.ssrn.com/sol3/papers.cf… /1
"tracing the origins of the 5 μm threshold...ultimately revealed a conflation between various understandings and definitions of 'aerosols.' Most contemporary sources use this threshold only to explain which particles stay suspended in the air for longer times,..." /2
"yet the 5 μm distinction is clearly not based on what stays airborne but on what reaches deepest in the lungs...." /3
Read 6 tweets
Linsey Marr Profile picture
11 Mar
Here's a 🧵summarizing my testimony on airborne transmission of COVID-19. Full version at edlabor.house.gov/hearings/clear… /0
COVID-19 is transmitted mainly by breathing in aerosol particles carrying the virus. Two other possible routes are 1) touching a sick person or contaminated object and 2) being sprayed by large respiratory droplets. These other routes are rarer. /1
Many cases of COVID-19 have been traced to “close contacts,” and this was incorrectly interpreted to mean that large droplets were responsible for transmitting the disease. /2
Read 26 tweets

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