UCSF Grand Rounds on Face Masks/Shields & droplet/aerosols

UCSF Grand Rounds on Face Masks/Shields & droplet/aerosols - Printable Version

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UCSF Grand Rounds on Face Masks/Shields & droplet/aerosols - M T - 08-06-2020

I've only had time to watch the first presenter (of 3) in the July 16 UCSF Grand Rounds video
https://www.youtube.com/watch?v=Cio3rh6ta3w
(Total video is 1.5 hours.)
I recommend this to those interested in air transmission of SARS-COV-2, and the role of face masks and face shields.
When I have time, I'll try to report some of the information covered.

Presenters:
Don Milton, Professor, Environmental & Occupational Health, University of Maryland School of Public Health

Monica Gandhi, UCSF Professor of Medicine; Associate Chief of Division of HIV, Infectious Diseases, and Global Medicine at ZSFG; Director of the UCSF Center for AIDS Research; and Medical Director of the HIV Clinic, Ward 86, ZSFG

Michael Edmond, Chief Quality Officer and Associate Chief Medical Officer, University of Iowa Health Care; Professor of Medicine, Division of Infectious Diseases, University of Iowa Carver College of Medicine

(Below the video are links to other UCSF Grand Rounds and related videos. Oops...CARDboard embeds the video. Go to Youtube and look at video Cio3rh6ta3w to see the links below the video.)

RE: UCSF Grand Rounds on Face Masks/Shields & droplet/aerosols - M T - 08-06-2020

Tidbits:
6:30 Breaks particles into different categories:
   Inhalable ≤ 100 microns
   Thoracic 10-15 microns
   Respirable: ≤ 5 microns
7:50 Comparison to TB & Measles. Neither has been cultured (or it is very difficult) from the air.
11:00 (Guinea pig?) lungs exposed to TB-infected aerosols >5 micron (no impact) or <5 micron(infected)
12:16 where depositional patterns by size is shown for different parts of the airways (Nose breathing. People exercising or panting will have different pattern.)
14:23 Medical vs Exposure science categorization of particles by size
14:45 Settling time in Still Air by particle size (minutes for 1.5m drop)
15:13 Travel distance of droplets in directional air flow to drop 1 meter
   5 micron travels 65m in 5cm/s; travels 270m in 20cm/s
20 micron travels 4m " " ; 15m " "
30 micron travels 2m " " ;    5m " "
   "2 meter cutoff doesn't make a whole lot of sense from an aerosol physics point of view"
With turbulence, it won't go so far, but will remain suspended longer.
The thermal plume of a human body will carry a 50 micron droplet upward.
16:34 RCT of spread of H3N2 influenza. Had difficulties getting spread as volunteers weren't shedding in aerosols. Minimal shedding in aerosols even though lots of virus in swabs.
Consistent with earlier experiments where aerosols were very infectious.
19:06 SARS & MERS spread by aerosols. The Amoy Gardens outbreak, if I understand him correctly, was an outdoor aerosol that infected people in buildings, depending on which buildings were exposed to the aerosol. (My understanding needs confirmation)
20:04 Patient bedside sampling of SARS-COV-2 show considerable virus in 1-4 micron and >4 micron aerosols.
21:22 Samples of SARS-COV-2 from surfaces & air(on personal samplers)
21:39 The restaurant infection in Wuhan including infection at 4.6m
22:30 1960s experiment that showed the route of the infection affects the severity of influenza.
23:10 Current experiments with Influenza. Cultured from breathing. (~ 1 culturable virus particle per minute)
23:45 Surgical ear-loop Mask vs no Mask source control experiments in 2013. Removed 5+-micron particles; reduced by 2x particles in fine particle size (< 5 micron)
24:30 Similar work on coronavirus cold viruses
25:10 Currently working on this at U of Md for SARS-COV-2
27:00 "[SARS-COV-2] is a lot more like TB than Measles."
28:00 I wouldn't get on an airplane. Talks about the wrong direction of vents in airplanes.

RE: UCSF Grand Rounds on Face Masks/Shields & droplet/aerosols - BostonCard - 08-06-2020

Here's the article about the Amoy Gardens spread of SARS.

https://www.nejm.org/doi/full/10.1056/NEJMoa032867

Quote:Residents of the floors at the middle and upper levels in building E were at a significantly higher risk than residents on lower floors; this finding is consistent with a rising plume of contaminated warm air in the air shaft generated from a middle-level apartment unit. The risks for the different units matched the virus concentrations predicted with the use of multizone modeling. The distribution of risk in buildings B, C, and D corresponded well with the three-dimensional spread of virus-laden aerosols predicted with the use of computational fluid-dynamics modeling.

Quote:The prevailing wind (red arrows) during the period of possible exposure was northeasterly, or roughly perpendicular to the exterior walls of apartment units Dc and Da in building E. The distance between buildings E and B is 60 m. The direction from which the wind blew shifted from nearly north to east and even southeast. The red dot in building E indicates the unit that the index patient visited. The directional indicator for the units at the lower right-hand corner indicates the direction each unit faced. In the directional code (Ab, Ad, Ba, Bc, Cb, Cd, Da, Dc) used to designate an apartment unit, uppercase letters denote front-facing windows and lowercase letters side-facing windows.

Quote:According to our computational fluid-dynamics modeling, the buoyant plume (blue) rose from the air shaft between two housing units in building E (yellow) and was carried by a northeasterly wind toward the middle-level floors in buildings C and D. The L-shape structure (Panels A and B) was a nearby construction site that blocked the wind flowing toward lower-level floors in buildings E, C, and D. The wake flow of the construction site created a region of negative air pressure in the space between buildings E, C, and D (Panel B) that caused the plume to bend downward, toward buildings C and D.