1/ Covid (@UCSF) Chronicles, Day 121
Grand rounds today, here: tinyurl.com/y5ut4435. As I said in my intro (@ 1:00), we covered perhaps the most important topics in the world today: how SARS-Co-V-2 spreads & what can be done to prevent it.
Grand rounds today, here: tinyurl.com/y5ut4435. As I said in my intro (@ 1:00), we covered perhaps the most important topics in the world today: how SARS-Co-V-2 spreads & what can be done to prevent it.
2/ I went thru the numbers yest, & no big changes: tinyurl.com/yyfp92bh @UCSFHospitals 28 pts (down 2), 9 on vents (stable). SF: 77 new cases/day, sl. up (Fig L). Hospital pts=99, most ever (R). Note: mostly non-ICU – ?healthier pts, better Rx? Not sure why, or if it’ll last. 
3/ Nationally, another record # of cases. @EricTopol tinyurl.com/y3s5javg & @alexismadrigal tinyurl.com/y9mzwc2h capture dire scene – from bad to worse, as D.C. continues with its “nonsense” – distractions like attacks on Fauci & on @CDCgov. Shameful, destructive, and sad.
4/ To Grand Rounds: Began w/ @Don_Milton on science of viral spread. An epiphany for me: “Aerosol scientists” like Milton think about mechanisms/particles differently than MDs. They think contact vs. splash & spray vs. inhalation; we tend to think aerosol vs. droplet ( @ 5:00)
5/ Each respiratory bug has unique characteristics, which influence ease/mechanism of spread, & utility of masks. For eg (@ 6:30), measles pts spew 2-10 “infectious doses”/MIN, w/ Ro>10; vs. TB pts put out ~1 infectious dose/HR, w/ Ro<2. SARS-CoV-2 acts more like TB than measles.
6/ Much is driven by particle size. Big droplets don’t stay in air long & get caught up in nose or eye (they might then travel to lungs later, but may not). Whereas smaller droplets can stay suspended in air longer (similar to pollen), & they can travel directly into your lungs.
7/ Issue of airflow: complicated. While more flow generally good, unidirectional flow can cause droplets to fly further (>6 ft). Turbulence (esp. outdoors, or indoors w/ exhaust vent) distributes virus in larger volume, making it less likely to get an infectious dose (@ 16:30).
8/ @ 1:17:30 in Q&A, Milton discusses famous restaurant-air conditioner case in China tinyurl.com/vp3fraf, in which people seated several tables from source patient became infected w/ Covid. Problem there: exhaust vents were sealed, so same air was being re-circulated by A/C.
9/ @ 1:27:00: Airplanes interesting: overhead vents force air down, but our bodies create thermal plume that forces it up; these 2 forces collide to move air laterally – not good. Milton: he wouldn’t fly (admits he is a very careful guy); other 2 experts (Gandhi & Edmond) would.
10/ Amusing: Milton developed a machine to detect viral particles that come out of people with breathing, coughing, etc. Its name, aptly: the Gesundheit (actually, it’s the Gesundheit II; there was an original Gesundheit machine, so this is Version 2).
11/ Practical implications: tho SARS-CoV-2 can be aerosolized, amount is small, likely needs prolonged exposure to catch. So surgical masks good enuf except for aerosol-generating procedures. @ 1:10:00: relatively small # of nosocomial infections supports minimal aerosol spread.
12/ @ 1:21:45, re: fomites (surfaces), all 3 speakers agreed that, while it was a major concern in Feb-March (Gandhi: “we didn’t know what was going on”), today, says Edmond, “I worry less about it.” But, though less concerned, all of them do clean their hands pretty regularly.
13/ @ 31:00, next: Monica Gandhi, describing hypothesis that mask-wearing may not only prevent viral spread (cases) but also lead to lower viral burden… and thus milder disease. I described this previously tinyurl.com/y2svp8f3 (panels 17-19), so won’t repeat that discussion.
14/ @ 35:40: ever-popular masked hamster made another appearance (Fig on L); Gandhi explains that the hamster didn’t actually wear a mask; masking was simulated. On the other hand (Fig R), there truly WAS a masked cat in this family pic from 1918 flu pandemic (Fig R), @ 46:30.
15/ @ 1:15:30, I asked Monica how she thinks about possible confounders – there are several explanations (other than masks) why there's more asymptomatic infections & lower Covid mortality. Response: it's multifactorial, but enough scientific/epi evidence that masks are a factor.
16/ @ 43:20, she makes point I’ve also made: while no one can absolutely prove that infection leads to immunity, there hasn’t been one credible report of Covid re-infection; seems like strong evidence that immunity is real. It's not just antibodies; cellular immunity is key too.
17/ @ 49:30, @mike_edmond @uihealthcare, discusses Iowa’s embrace of face shields – borne of necessity due to mask shortage in March. After trying face shields, they became advocates – especially for use in the community, as they described in @JAMA_current tinyurl.com/ybbw76sy
18/ @ 55:20: Many flavors of face shields, including ones that attach to baseball caps, cute ones for kids, and ones for Devo fans. As Edmond says, the most important thing, in the end, is that people actually wear protection – whether it's masks or face shields.
19/ Edmond cites advantages of face shields, esp. for community use. Maybe less in hospital where mask is also needed because of spaces around edges of shields. @UCSFHospitals, we’re now requiring eye goggles plus masks for MDs/RNs – probably equivalent to shields plus masks.
20/ For more on the aerosol/droplet question, excellent review in this week’s @JAMA_current by Klompas et al tinyurl.com/y3ll8hll Authors agree that there is some aerosolized virus, but also that the epidemiological data are not consistent with widespread spread via aerosol.
21/ Key point by Edmond @ 1:05:00: perspective of occupational health (ie protecting healthcare workers) is to prevent ALL cases, given frequent exposure. Whereas public health perspective emphasizes how to lower (maybe not eliminate) cases in the most feasible, sustainable way.
22/ Illuminating discussion. Won’t change my practice (surgical mask plus goggles in hospital, surgical mask elsewhere; N95 for hi-risk encounters). I see merit of face shields in community, but changing our message again seems too confusing. Shields are a legit alternative.
23/ That’s it for now. Again, encourage you to watch whole Grand Rounds if you have time (90 min), it's available @YouTube here: tinyurl.com/y5ut4435
Back tomorrow with weekly round-up. Till then, stay safe.
Back tomorrow with weekly round-up. Till then, stay safe.
