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Linsey Marr https://www.threads.net/@linseycmarr Profile picture
Linsey Marr https://www.threads.net/@linseycmarr
@linseymarr
Engineering professor @virginia_tech with expertise in airborne transmission of viruses, air quality, nanotechnology. Avid recreational athlete.
36 subscribers
May 30, 2023 • 5 tweets • 1 min read
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.
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Mar 24, 2023 • 4 tweets • 2 min read
We determined size and chemical composition of >35000 respiratory particles from 3 healthy subjects. Desiccated size 0.05-4.4 µm. Composition was size-dependent. Free preprint drive.google.com/file/d/1B4KKav… @ajprussin @PNNLab pubs.acs.org/doi/10.1021/ac… Particles were mostly C, some Na+P+K+Cl, heterogeneous. /2
Dec 1, 2022 • 4 tweets • 1 min read
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
Nov 14, 2022 • 8 tweets • 2 min read
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
Oct 26, 2022 • 4 tweets • 3 min read
“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
Oct 18, 2022 • 9 tweets • 2 min read
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

pubs.acs.org/doi/10.1021/ac… Free preprint at drive.google.com/file/d/1nkQHPK…

"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
Oct 12, 2022 • 10 tweets • 7 min read
🧵of my perspectives from the White House Summit on Indoor Air Quality. I was flabbergasted, in a good way, to see this happen. Thanks to @AshishKJha46 for elevating this subject and all the participants from gov, industry, education, research. Link to video below. Agenda... /1 1. @AshishKJha46 emphasizes the potential for improving health by ensuring clean air
2. @j_g_allen calls for building "tuneup", ventilation targets
3. Panel on schools with @SuptJaraCCSD @DrAlexMarrero. Need standards to elevate IAQ to a "must do." /2
Aug 17, 2022 • 4 tweets • 1 min read
Study confirms that HEPA filters work on SARS-CoV-2, of course. Note that antiviral coating doesn't affect removal from air, since it's a physical process. I sketched expected ratio of concentration at time t to initial concentration as function of t. /1 journals.asm.org/doi/full/10.11… Deviation from theory expected due to imprecision of titration assay, imperfect mixing in the chamber, wall losses, flow calibration, etc. This is basic aerosol science. /2
Jun 7, 2022 • 12 tweets • 3 min read
New viewpoint in @JAMA_current from CDC authors urges using American Rescue Plan funds to upgrade HVAC systems in buildings. Lots of strong words: /1 jamanetwork.com/journals/jama/… "Because no single approach is 100% effective in preventing COVID-19, prevention measures work best when layered, including vaccination and nonpharmacologic interventions that reduce inhalation of infectious particles." /2
May 31, 2022 • 7 tweets • 5 min read
I know very little about monkeypox, but I'm going to weigh in to correct misunderstanding about mechanisms of transmission. Someone claimed, "[monkyepox] virus itself is much larger and heavier and unable to travel as far" because it's DNA not RNA. nytimes.com/article/monkey… /1 How far a virus can travel is determined by the size of the droplet/aerosol carrying it, not the size and weight of the virus itself. But that's just one factor among many that determine whether a virus can be transmitted via the airborne route. /2
May 22, 2022 • 10 tweets • 3 min read
On our way to Orlando for some end-of-the-school-year fun at the Wizarding World. Ventilation in the Raleigh-Durham airport is good. Not the worst I've seen on an airplane, a Boeing 737.
Mar 31, 2022 • 6 tweets • 3 min read
Human challenge study finds infectious dose of 10 TCID50. "36 volunteers aged 18–29 years without evidence of previous infection or vaccination were inoculated with 10 TCID50 of a wild-type virus (SARS-CoV-2/human/GBR/484861/2020) intranasally" and 18 became infected. /1 This is a correction to an earlier tweet I deleted, shown below, in which I described 1 TCID50 as 1 virus particle. /2
Mar 17, 2022 • 5 tweets • 1 min read
Good ventilation and filtration prevent the coronavirus and other contaminants from accumulating in the air and thus reduce our exposure. White House spurs efforts to achieve clean, healthy air in buildings. whitehouse.gov/briefing-room/… /1 New Clean Air in Buildings Challenge at epa.gov/indoor-air-qua… See pdf link at bottom of page. The guidelines address HVAC operation and maintenance, optimizing ventilation, filtration and air cleaning, community engagement. /2
Mar 11, 2022 • 9 tweets • 2 min read
I spoke with @LaurenPelley about a new preprint comparing survival of Omicron vs. ancestral strain on surfaces. TLDR Omicron is more stable (probably in aerosols too, may contribute to greater transmissibility, my graph of their data👇) /1 Both lose ~1 log in the first few hours, then Omicron almost levels off while ancestral continues slow decay. Decay is much faster on paper and tissue (not shown), consistent with prior studies. /2
Feb 11, 2022 • 9 tweets • 5 min read
New special issue of @RSocPublishing #InterfaceFocus on airborne transmission of SARS-CoV-2 royalsocietypublishing.org/toc/rsfs/2022/…

Intro royalsocietypublishing.org/doi/full/10.10… by Tang, Li, Eames, and me summarizes the contents. /1 "Spread of infectious agents through the air in complex spaces" explores effects of buoyancy, turbulence and their influence on how far aerosols travel, also effects of turbulence and stratification on the spread of infectious agents indoors. royalsocietypublishing.org/doi/full/10.10… /2
Jan 25, 2022 • 8 tweets • 4 min read
Delighted to have collaborated with @MicroLevitator @jfdavies and team to continue our deep dive into understanding mechanisms of virus decay in droplets and aerosols. /1 Levitated aerosols of various model fluids--we did not test any real respiratory fluids--evaporate and become semi-solid at moderate relative humidity (RH), solid at low RH. Diffusion of potential disinfectants would be inhibited, slowing kinetics of decay reactions. /2
Jan 3, 2022 • 4 tweets • 3 min read
Some thoughts for the new year:

How do we do public health better in a country with such a strong culture of individualism? /1 The reluctance to promote rapid tests and N95s is due in part to rules for diagnostics and worker protection (@michael_mina). If the boat is sinking, I'll take any life vest I can get. /2
Dec 21, 2021 • 5 tweets • 2 min read
Our paper (@isjinpan @ajprussin Duggal lab) on SARS-CoV-2 on surfaces and HVAC filters in dorm rooms housing infected students is now published pubs.acs.org/doi/full/10.10… /1 Free preprint
drive.google.com/file/d/1LB0sb-… /2
Nov 18, 2021 • 4 tweets • 2 min read
@theNASEM webinar on Public Health Lessons for Non-Vaccine Influenza Interventions: Looking Past COVID-19 today at 1 pm nam.edu/event/advancin… Report released yesterday at bit.ly/3kHhZeW /1 The report recommends use of respirators, surgical/procedural masks, and multi-layer woven cloth face masks to reduce transmission of SARS-CoV-2, and states that face shields alone are not effective /2
Oct 22, 2021 • 20 tweets • 3 min read
Tang & I wrote about updating transmission routes to inhalation, spray, and touch, following up on suggestions by Yuguo Li and @Don_Milton. academic.oup.com/cid/advance-ar… /1 "Current infection-control guidelines subscribe to a contact/droplet/airborne paradigm that is based on outdated understanding. Here, we propose to modify and align existing guidelines with a more accurate description of the different transmission routes." /2
Oct 21, 2021 • 8 tweets • 2 min read
Great editorial about "The COVID-19 crisis is almost certainly an indoor air crisis; it is very likely a ventilation crisis." (among other crises) onlinelibrary.wiley.com/doi/full/10.11… by Nazaroff @WBahnfleth @WargockiPawel Zhang /1 "The phenomenon of low risk outdoors and high risk indoors deserves some explanation. This is probably the most important observation in this pandemic. There is a simple explanation: dilution." /2