Covid-19: How the Virus Gets in and How to Block It: Aerosols, Droplets, Masks, Face Shields, & More

good afternoon welcome back to ucsf uh department of medicine grand rounds i'm bob wachter chair of the ucsf department of medicine welcome again to our live audience in our department and throughout ucsf as well as our friends and our partner sites in the ucsf health network as is our usual practice so we will post this video at about 7 30 p.m tonight on youtube i will tweet out the address uh and uh our prior rounds that we've been doing since this started have been viewed more than 300 000 times so that has been terrific a few quick ground rules the same as usual put your zoom screen in zoom window in full screen mode if you have questions put them in the q a box and my colleague quinny chang is monitoring those and will pitch some of them to me unfortunately a virus continues its rampage through towns and cities uh throughout the united states in the world causing an enormous number of deaths now up to about 140 000 the u.s and nearly 600 000 in the world as well as exacting a terrible toll and an illness both acute and chronic on top of that we've seen a massive disruption social disruptions economics psychological disruptions with significant disparities if you think about it this means that the two most important questions in the world right now are how does sars cov2 spread from one human to another and what are the best ways to stop it uh you might challenge me and say when are we going to have an effective and safe vaccine and i would grant you that is also a very important question but we'll focus on the first two today uh how does the virus spread and what are the most effective ways of stopping it from spreading uh we're very fortunate three experts world experts in this to speak to us today uh one from ucsf to from other institutions who are joining us the three speakers are don milton don is professor of occupational environmental health at the university of maryland school of public health based in college park maryland don has served on multiple advisory boards for uh for journals as well as the nyash indoor environment environmental team he's one of the world's leading experts on the way that infections spread through the air which turns out to be a hot topic he'll focus his comments on this particularly on the question of droplet versus aerosol spread and why this distinction is crucially important our next speaker will be monica gandhi monica is well known for to those at ucsf she's professor of medicine associate division chief for clinical operations and education in our division of hiv infectious disease and global medicine uh based at zuckerberg san francisco general hospital she also is the director of the ucsf gladstone center for aids research cfar and medical director of the hiv clinic ward 86 at san francisco general uh monica's research is focused on identifying low-cost solutions to measuring antiretroviral levels and resource poor settings as well as many other topics but like many of our hiv researchers she's uh added to her focus uh how do we prevent covet and she's taken a particular interest in the role of masking not only preventing infection but potentially mediating the kind of infection that people get i should also mention that monica just last week or two weeks ago uh co-chaired the uh the international aids conference that was held here in the bay area and uh and broadcast virtually and having been the program director myself of the 1990 international aids conference i know what a massive undertaking that is so congratulations on a very successful conference our third speaker is uh michael edmond mike is chief quality officer and associate chief medical officer at the university of iowa hospitals and clinic he's also a clinical professor of infectious disease at iowa's carver college of medicine mike is a leading expert on the epidemiology of healthcare associated infections and public policy implications of infection prevention he and his group have uh been strong proponents of the use of face shields uh and an interesting practice and one that we'll hear more about when mike speaks so really looking forward to a wonderful uh session on really one of the central issues that we're all struggling with right now so our format will be this each of the three speakers first don then monica then mike will give lectures lasting around 15 minutes with some slides i'll follow up with a couple of questions for each of them and then when all three are done at 12 50 12 50 or 12 55 or so we'll take about 20 minutes going to 15 for a discussion with all three of our experts so with that let's go ahead and get started with don milton don you are on and you're on mute ah good okay here we go thank you um so it's a great pleasure to be here today and to be able to share some of my perspectives with you on infection transmission and infectious droplets and drops and aerosols next slide so what are the transmission modes generally of respiratory viruses well they fall into generally three categories contact where there's patient to finger or fomite to finger and then finger to eye nose or mouth transfer to inoculate mucous membranes a splash and spray transmission where ballistic droplets get a direct hit in your eye nostril or mouth and inhalation exposure where one can inhale inhalable aerosols thoracic aerosols or respirable aerosols and we divide aerosols into these three categories because it's important it depends on size as to where they can deposit in the respiratory tract and we'll come back to that and as you can see in this illustration one of the key roles of masks is that it reduces the amount of respirable aerosols and pretty much eliminates the larger aerosols and splash and spray generation from infected persons so next slide in comparison with known aerosol transmitted infections so often you hear about people contrasting what's happening in covid19 with measles because measles has a very high dose generation rate of very high basic reproductive number and it targets cells in the airway and in the alveoli so that it can initiate infection when deposited at various levels in the respiratory tract and in terms of environmental sampling there's only one attempt that i'm aware of that has been made to detect the rna in the air was done at wake forest by werner bischoff and his group they were unable to culture it from the air but they were able to easily detect the rna on surfaces because of this massive the high generation rate two to ten infectious doses seem to be being generated per minute incidental contact is important long-range transmission has been evident in some settings but usually people are nearby but you can pick it up especially when it's not prevalent that people have been infected by a source at a distance i haven't seen any studies looking at face masks in measles tuberculosis is a completely other end of the spectrum of airborne infection it has a very low rate of infectious dose generation prior to hiv and talking about instead of two to ten per minute less than one to about one infectious dose per hour the target is in the alveolus so aerosols have to be in the fine particle size that can reach all the way to the alveolus to cause infection and aerosol sampling is uniformly negative in tb except when you have somebody cough directly on a sampler that's placed in a confined box so you don't get too much dilution it's easily detected on surfaces and for this reason up until the experiments in the early 19 or mid 1950s that riley performed in the baltimore va showing that you could infect guinea pigs through the ventilation system it wasn't conclusively understood that it was potentially airborne and now we understand that it's an obligate airborne infection the uh reproductive rate is quite low relative to influ to measles and and historically most transmission was recognized as having required prolonged close contact long-range transmission was only evident in the united states anyway after it was no longer endemic and recent studies have shown that face masks are quite effective reducing about two-thirds of the virus uh the bacteria shed into the air so that protecting sentinel guinea pigs used to study the tren airborne transmission but note here that we have something that is we know airborne transmitted it's easily detected on surfaces the r knot is not very high and it's very difficult to detect it much less culture it from the air sound familiar this is uh one of the famous uh experiments done by william wells early on uh i think this was in the 40s he actually did this work showing that when he generated tuberculosis aerosols in defined particle sizes that he could only infect experimental animals if it was in respirable particle sizes so where does sars two virus bind well the most recent work on this looking at ace2 receptor distribution shows that we have lots of receptors in the bronchus we have receptors in the alveoli and in the conjunctiva and we'll hear more about face shields and eye protection in a little bit and this emphasizes why that's important there's also a lot of receptor present in the oral mucosa thus we are vulnerable through that root as well potentially there's probably more to this than just having ace 2 expressed on the cells in cell culture we know that for example expression of certain proteases on varroa cells very much increases their uh susceptibility to infection and uh production of virus after infection uh the next slide we see the uh the deposition pattern where things deposit on the left axis you see the respiratory deposition uh fraction and by particle size on a log scale so you see between about 10 or 15 and 100 microns you can inhale it it'll deposit in your nose as it gets smaller we begin to get things into the tracheal bronchial tree and then eventually into the alveolus but when we get down to the size of a naked virus the deposition drops off because the lung is not a very good filter at that size so this gives you an idea of where these deposit even at these moderately small sizes of a few microns most of it's still landing in your nose next slide so there's two ways to define droplets and particles that carry respiratory viruses the medical categories tend to be respiratory droplets and aerosols with a definition of aerosols that says that they are only things less than five microns in diameter and everything is bigger than that is a droplet assumed to deposit close to the source in an exposure science we look at it very differently we recognize that we can inhale things up to 100 microns and they don't get past the nose as the previous slide showed we call those inhalable aerosols that that somewhat that smaller aerosols starting around 10 to 15 microns can get past the nose past the larynx into the trachea and main stem bronchi we call these thoracic aerosols and then finally aerosols that deposit all the way out in the terminal bronchioles and alveoli and these are respirable aerosols and in air pollution you will frequently hear them referred to as pm10 which is more or less the thoracic fraction and pm 2.5 the respirable fraction so this is very much in contrast to the medical categories next slide shows the settling time of droplets in still air which shows that 10 microns and smaller can remain suspended for many minutes in still air as you get larger if the residence time in air is only a few minutes but next slide if you have movement of the air indoors and indoor air is not still droplets can travel much farther than 2 meters as shown here if you have very low velocity of 5 centimeters per second indoor air a 5 micron particle will still travel about 65 meters a 10 micron particle 15 meters a 20 micron particle 4 meters and when you begin to get a little higher velocity you have a fan blowing an ac system running then things begin to be able to move very far even a 30 micron particle can go five meters so the two meter cutoff doesn't make a whole lot of sense from an aerosol physics point of view but with turbulence rather than just purely directional flow you're not going to see it go that far what you're going to see is that it's the main effect of this is going to remain suspended in air for a lot longer just the thermal plume off of a human body is enough to carry upwards a 50 micron droplet the upward velocity of air from around your body is greater than that of the settling velocity of a 50 micron droplet next slide so one of the things that we keep getting asked for is well we need a randomized controlled trial of transmission well i encourage you to look at this paper that was published on monday and plus pathogens we've tried to do that with influenza and in this study we inoculated volunteers with an h3n2 and then had them spend four days more than 12 hours a day in close contact with uh volunteers who were also zero susceptible to this uh gmp virus but the volunteers who were inoculated were not shedding very much virus into the aerosol as we were collecting the aerosol shown by the the gesundheit ii sampler up in the upper right and but they had lots of virus in the np swabs and the ct values were in the mid 20s still even though they spent four days together with susceptible volunteers we were only able to get very minimal transmission now granted that we inoculated people in the nose with the virus and we know from work done at fort dietrich in the 1960s that and before that in orphanages in new jersey and in the 1960s they were using maryland penitentiary prisoners when they used the same virus to infect by aerosol it took a single tcid 50 to cause infection in a sero-susceptible subject and they got full-blown flu symptoms it took hundreds of tcid 50s to cause infection by nose drops and usually people were totally asymptomatic just zero converted and tens of thousands of tcid50s to cause any symptoms and then the symptoms were usually mild upper respiratory infections next slide so um what do we know about aerosols and sars and mers there was a report in the new england journal in 2004 about the amoeba gardens apartments outbreak which is a very unusual setting where a fecal aerosol was apparently generated there was a lot of question about was there direct contact were there elevator buttons pushed many of the cases were in the the building e that was the uh epicenter of the outbreak but um the the the pattern was hard to explain as to why people in building f g a didn't get infected whereas people in c and d especially were very heavily affected until this computational fluid dynamic model of how airflow was occurring at the time of this outbreak seemed to explain it also a multi-zone model of the building showed exactly where infections happened mers has been cultured from a sample in the air outside of a patient room in south korea a few years ago so there is some data suggesting aerosols are important in some settings with sars and mers next slide with sars co v2 air sampling in singapore whereas the initial study was not able to detect that a follow-on study in the same unit was able to detect sars cov2 using a more extensive and well-designed sampling out set up especially with the work of a postdoc who has expertise in aerobiology and there we saw that there was considerable aerosol in the one to four micron and the larger than four micron particle sizes next slide in a report from wuhan with expert industrial hygienists from the hong kong university of science and technology using a personal samplers they were able to detect viral rna and very small particle sizes no one's cultured it from the air yet but then again no one's cultured measles or tb from the air either next slide uh this is from the scent the arpa pre-print uh showing that they were getting rna on area samples but the striking thing to me was the very high concentrations that they picked up on personal samplers next slide this is a analysis by a group of engineers and infectious disease experts from hong kong university of the guangzhou restaurant outbreak where they've done tracer gas studies and careful modeling and video analysis of where people in the room were and how long they were there which shows that the aerosol would have been contained in the back end of the room based on the way the air circulation was was working in that room and that infection appears to have occurred over distances of almost 5 meters next slide so i mentioned earlier the work uh at fort dietrich in the 1960s where they showed that the importance of not only the dose of influenza but the root of influenza and suggests that influenza is an anisotropic infection the root makes a difference as to how severe the illness is not only the dose and you'll notice that on this cough collection device here it says gesundheit on the side so when i developed my device here we called it the gazoon type 2 next slide and this device is a dynamic aerosol sampler which collects coarse aerosol up to 80 microns uh fine aerosol down to 50 nanometers in size and we have been able to culture virus uh from uh the breath of a study we did with 142 influenza cases and estimate that the aerosol generation rate from influenza cases is about one culturable virus particle per minute and that the coughing was associated with increased shedding but coughing was not required for shedding of rna or infectious virus that we could culture next slide we use this device to study masks the source control in this paper in 2013 where we had paired samples from each subject with and without a mask and show that mass pretty much eliminated the coarse aerosol greater than 5 microns but only reduced but not eliminated the aerosol in the fine particle fraction but it was cutting it by about a factor of a little more than two so overall it cut out two thirds of all the virus being shed by these subjects next slide this same device was used by colleagues in hong kong and published in nature medicine earlier this year looking at coronaviruses seasonal coronaviruses unfortunately these are not all paired some of them but not all of them are paired samples and given the wide range of shedding from individuals one has to take the finding that it completely blocked fine particle aerosols with a grain of salt but clearly it appears that this what works with flu is working here with coronaviruses as well next slide um we uh the one we are now ongoing doing these studies with covid cases at the university of maryland uh and hope to be able to present soon results of these studies and our attempts to work with matt freeman and his bl-3 in baltimore with his long experience was coronaviruses to see if we can culture it from air thank you great thank you don um ton of questions i'm going to give you one or two but then we need to move on um still trying to noodle over what the implications of these findings are for for masks and which type of masks one needs i think you know people sort of understand if it's mostly droplet then you require one kind of mask if it's mostly aerosol that may or may not work uh so just sort of in terms of practical clinical decisions that a doctor or nurse needs to make about what kind of mask and where where the risk is how would you distill that i would say that um well you we're talking about there are two situations here there's general public and then there's in the healthcare setting and in the healthcare setting we tend to have especially here in the u.s less so in some other places high air exchange rates in patient care areas even not airborne isolation units our hospitals are supposed to be to give their changes so we should get a great deal of dilution by that so that the aerosol is contained in the near zone close to the patient and uh if you're outside of that near zone uh your the the exposure is going to drop to quite low levels and what we're seeing is that the suggestion that this is a lot more like tb than like measles in terms of the source strength of aerosols the people are shedding some and if you're up close and for a long time then there's a real risk of aerosol exposure but farther away and certainly the other thing is one thing we have going in healthcare is that often we're seeing patients later on in the illness which we know they're already making response and it's difficult to culture virus from them things i think are adding up to protect us in health care thank you um and i'm sure the static is on your end or my end but uh we'll keep going for a sec um the question about uh airplane flight comes up all the time so based on what we now understand about spread what what you tell people uh about plane flights and what do you do well i heard tony fauci being interviewed on the jama blog the other day saying he wasn't about to get on an airplane and i'm not either okay and the reason why based on well i was part of the airline cabin environment research center of excellence for faa 20 years ago and you know i understand something about airplane cabins the large jets are pretty much all heap of filtered but because they're blowing the air from the top and out the bottom they're fighting against the thermal plume of the heat from people's bodies which wants to take the air up if they would reverse the airflow take it from the floor hopefully they're going to do that someday um i think we're going to we're going to we're going to actually look at i think your audio is a problem right now so i think kyle's going to work and let us go ahead and move on to uh uh to our next speaker so our next speakers monika gandhi will bring down on at the end and we will uh talk through some of the other issues that have come up including including fomites and the role of ventilation so uh monica i've already introduced and she's going to talk to us about the role of mass including some potentially exciting uh new thinking about that hi well thanks for having me here so um we're going to talk about how cobin 19 severity may um be dose depending essentially and then that will relate to masking so next slide please so the outline of this next slide sorry the outline of this while we're waiting for that to advance is that i'm going to talk about kind of an age-old theory that the dose of virus that you get in actually determines how sick you get and we're going to talk about that issue of the viral inoculum and the severity of disease and the theory behind that and how masking would then decrease the viral inoculum and then we'll talk a little bit about if asymptomatic infection is increasing under mass conditions we could mention san francisco and other countries and then we'll talk about the possibility of population level immunity resulting from that so i think we're still waiting for um the slides to advance sorry should i wait a minute or should i keep going we're working out okay so then um so one question that comes up is what is the rate of asymptomatic infection now um and in the world um and right now the the the most likely rate that we have with asymptomatic infection with sars cov2 is about 40 and uh that comes from really well designed studies like um this study that was done by dr diane havelier and karina marquez and gabe here that mass tested the mission district that you presented here in medicine grand rounds and then not only did they mass test everyone but they follow them out for two weeks and by doing that um so go to the next one and then the next one thank you so by doing that you can really say okay how many people are asymptomatic if you follow them out for two weeks were they pre-symptomatic or asymptomatic and the rate was 42 in their study and then two days ago the cdc came out with this number that mirrored what um dr haveler's study had shown which is about a 40 asymptomatic rate uh with this particular virus so that's where we are in the world with asymptomatic infection with covid next slide so then what about masking so you know we've known since late february and early march that high viral loads come out of your nose and mouth even when you're asymptomatic actually the epidemiology had hinted at something crazy like that because it had been spreading way further than we ever could have imagined based on its genetic relatedness to sars and so because of that that high viral shedding from your nose and mouth even when you feel well that really says okay cover that up to protect others so masking guidelines were put out by the cdc on april 3rd world health organization took um quite a bit longer actually uh and june 5th and then here in the city of san francisco masking was mandated on april 17th with a lot of enforcement and sort of stronger recommendations on may 28th and a lot of evidence that you um protect others by masking but the question of this talk is how do masks protect you so as we um will we can get into airborne versus chocolate later but really masks filter out a majority of viral particles but not all n95 masks filter out more and isolation mask and cloth mass filter out the majority of viral particles depending on what it is um between 65 and 85 and so the question is by wearing a mask do you get exposure to less virus and that does that lead to less severe disease next slide please so this is actually an age-old concept um so in 1938 this is the oldest paper i could find on it um this was the first paper that describes this phenomenon that the less virus that you get in the less inoculum that you get in the less likely you are to get sick so this is the concept of the ld50 or the lethal dose at which 50 of people get sick um and this was a study in mice that it looked like a 50 um the ld50 of a particular virus was x you know when they gave too much virus then the poor mice died and a little virus the mice didn't get very sick at all so this is one of the oldest studies on this next slide and then there's been a bunch of studies in other animals but it isn't actually ethical to give humans a lethal virus and say okay you know at what percentage do half of humans die and so um so the studies in humans have been done with with less lethal viruses and so this was a study published in our premier um infectious disease journal cid in 2015 that looked at giving humans influenza a in anticipation of a vaccine and with this wild type influenza a the more that you gave humans the more sick they became they had a lot of cough and shortness of breath and if you gave them a little bit they didn't get very sick at all so that is some evidence in humans and then finally next slide this is a study from an animal study um in hamster model this was with stars kobe 2 the virus of interest of the day that causes covet 19. i'm sorry can you go to the next slide and i'll come back to this sorry about that so this is a study in little hamsters and um in this case what they did is simulated masking they didn't actually put that ten-year-old mask on that tangle hamster but um they simulated masking with surgical mass partitions and um the masked hamsters or the ones under mass conditions were less likely to contract stars kobe 2 but beyond that those who did contract sars kobe 2 had mild disease they were less likely to get sick please go back to the previous slide so indeed this kind of idea of high infectious dose and causing more mortality was uh the subject of a paper in clause 1 in 2010 which looked at why with the influence in 1918 pandemic we had a higher mortality rate with our second wave than with our first weight that's actually not usual usually you have more immunity going on and the second wave is much less sickening but in this case our second wave with influenza the pandemic in 1918 caused a higher mortality rate as seen on that slide on the right on the picture on the right and what this study postulated is it was that exposure to the higher infectious dose in the second wave with the crowding with world war one with people being uh too close together um that led to that higher mortality rate and that actually is reminiscent of what has been happening with sars kovi ii at the very beginning of it before we knew about masking we saw a lot more exposure to higher doses we saw healthcare workers getting more sick before we universally matched in this country around march 25th we had greater deaths among healthcare workers in italy and in new york we didn't know about masking and certainly household contacts are more like likely to get sick than someone that is exposed to someone with stars kobe 2 um outside of the household next slide and then next slide so then let's go to the question of okay if we've convinced ourselves the viral inoculum matters and that facial masking reduces that viral inoculum then have we seen more asymptomatic infection under masked circumstances and in places that mask when cases go up to severe illness and death go up and then let's find with it and with a hopeful note that with asymptomatic infection could you get immunity and then you've really had your um you've had the benefit of increasing asymptomatic infection next slide so this is a nice example i think of that question of um do rates of asymptomatic infection increase under mass conditions i think cruise ships are nice places to do experiments unfortunately you can't actually do the experiment again where you randomize the city to masking and randomize the city to unmasking and let it rip but even though we're kind of doing that experiment in the united states at some level but in this case this is for cruise ships so here um you know these are closed settings people aren't coming in and out and in this case um one of the earliest examples of a cruise ship where there was an earthquake with the diamond princess cruise ship and um the proportion and i reference article there of asymptomatic infection was 18 and no one was wearing mass of course we didn't even know about that and then of course the cdc as i told you um estimates the rate of asymptomatic infection of 40 and then this later cruise ship and this is um the study is here in the middle of the copen 19 in the footsteps of vernon shackleton this was an argentinian cruise ship and in this case there was an outbreak and they didn't let the cruise ship dock but they must have thrown mass over the side because they gave all the passengers surgical mass and they gave all of the um crew and 95 masks who were serving the passengers who were ill and there was um a spread it's a closed setting there was 128 of 217 passengers who got ill but the rate of asymptomatic infection in that mass setting was 81 as opposed to 40 or 18 and we've seen that in other settings there was a pediatrics hemodialysis unit outbreak in indiana where everyone was masking there were cereal convergence but no one became ill and then there were two recent outbreaks in the united states one was in a seafood processing plant in oregon one was in a um tyson chicken plant in missouri and in both settings the the plants have been giving their workers masks and there were major outbreaks in both but 98 95 of workers remained asymptomatic next slide [Music] and then do we see this um kind of on a population level have we seen this ecologically have we seen this in other countries i think we do need to pay a little more attention to what was going on in other countries absolutely ecologically these sims true beyond the fact that there are countries who are used to masking from the sars pandemic and that would be of course singaporean thailand and vietnam and japan and hong kong and other countries it is true that as they opened up people really are good about masking it's very compliant masking environment and the cases went up and not deaths but let's turn to a country that wasn't used to mass gain this was the czech republic and on march 23rd the leadership of the czech republic said you know what everyone has to mask and everyone was home and they were making like cloth masks and everyone masked um and what happened is that they would open up and you can see the who data at the bottom they would open up and they and they would like get cases but they wouldn't get severe illness and then um they kept masked and they didn't get those deaths and they've had a total of 359 deaths as of yesterday i believe and on may 11th they've eased their restrictions on wearing masks so this was a truly kind of newly masked culture which was the czech republic next slide and one model shows in the references there that you can actually achieve a very low death rate um in the setting of masking this was a nice model that's been um cited a lot but if you look at social distancing after you ease your lock down that's the gray line and you can see that there are a lot of no without masking there are a lot of deaths and then in this model if you lift the lock down but 80 percent of the population is masking then the death rate remains flat 50 masking doesn't give you as good of a death rate so it's really that kind of 80 that's where we get this idea that we want 80 of the population to mask um and you know lockdown is a very blunt instrument but it does enforce behavior change because if nothing's open then you can't go anywhere um but masking does take behavior change like condoms um or clothing closing black houses you know in 1983 in san francisco condoms takes behavior change and so does putting on a mask next slide so what about san francisco we do test a lot um i think we're compliant um i don't think everyone's quantitated it our asymptomatic infection is up um and this is a just from last week a bay area technology company who labs processed i think 30 000 tests and a majority of those were in asymptomatic or mild uh symptoms and then this is the latest latest san francisco dph data from this morning and we do test a lot 200 000 tests almost um we have had cases go up since we eased restrictions here but luckily since june 27th we've only had one additional death um so it was 50 on june 27th where we had 3 500 cases and 14 50 cases later just one additional debts so we are keeping death rates very low here um which is great next slide um so is asymptomatic infection horrible is my last point yes it's horrible because you can spread unwittingly um you can have high rates of shedding from your nose and mouth even when you feel fine and that is the entire point why april through the cdc said mask however the hopeful thing about asymptomatic infection is that it is possible you can get immunity without long-term consequences and let's ignore this antibody stuff i think you know um many of us who work with viruses know that it really is cellular immunity that we should be looking at um if we looked at hiv antibodies that certainly doesn't protect you from infection that is um that is in fact how you diagnose hiv so let's think about cellular immunity and there's a lot of hopeful papers coming out about cellular immunity with chronoviruses with stars kobe 2. we've seen this with other chronoviruses and one um cited by dr fauci yesterday uh was about giving macaque sars kobe to infection and then protecting against we challenge another hopeful sign for immunity is that unfortunately we're eight months into this pandemic and counting and we have not seen a single convincing case of reinfection we've seen lots of long-term shedding but not a single case of um reinfection that we're persuaded about so that's very hopeful for immunity as well and asymptomatic infection is less likely to give you those longer-term consequences so there are a lot of good things about asymptomatic infection next slide so i'll just end with yesterday two days ago was a big day with fermaski the mmwr put out this hairstylist salon that if you mask no one was getting infected the jama two days ago published this healthcare worker study from boston that everyone in boston just like we did did universal masking in hospitals with surgical isolation masks in march 25th and we've been seeing healthcare worker infections very low since then and basically the cdc director said two days ago if we all messed up we could get rid of this in four six eight weeks we could be done um and then next slide yesterday wasn't a good day for masking on the other hand the georgia governor explicitly avoided masking orders in 15 localities yesterday and so i would end this talk with let's stop this nonsense like faucia said and let's mask up do you want to fight and with a final thing that really don't use those valve masks those are actually bad for you they um they exhale viruses they um so don't use those ones with valves that we used during the fires and then final slide in conclusion um masking may have more than one advantage during isolation um maybe the person at home should wear their mask like they do but so should their contacts this is an old theory that the less viral inoculum you get lose less severe disease it's hopeful but don't yell at people don't wear their masks i think harm reduction is better um masking is very effective and maybe as effective as lockdown in one model and let's look at other countries to see that and the us unfortunately may become a natural experiment where some places mask and some places don't but hopefully we won't um see that much longer and cell mediated immunity is a good thing and let's look at that and then the final slide is a picture from 1918 um next slide where you could see this little cat um and that cat is even masked so if that cat can mask we can mask too thank you thank you monica so the cats can mask the hamsters and not at this point uh people have asked about the type of mask you didn't really go into cloth versus surgical versus n95 as you think through this theory doesn't make any difference i think it does um but that doesn't mean that people should be wearing n95 masks out there and in fact i'm quite very clear on that point as we all are in the healthcare setting that n95 should be kept for aerosol generating procedures for healthcare workers that's really our decision here at ucsf and elsewhere and so the n95s are also super uncomfortable and it cuts down on acceptability so out there in the world in the public people can wear those surgical isolation masks or they can wear cloth masks and that really is sufficient we don't get into the breathing zones of people like um you know you do when you're having someone giving someone a nebulizer so this is really sufficient and i looked back at the old data of masking and this has been sufficient for airborne and droplet in public again in public where you're not in people's faces so it really is cloth or this and uh maybe one last question for you now before we move on you mentioned the what we had to do to get people to wear condoms and uh for hiv there's a huge history and hiv of trying to figure out how you make behavioral change stick um and that is in some ways the lessons here is sort of less important what the politicians do as and more important what people do every day and decisions they make so what are the what are the lessons from hiv that we should be thinking about as we try to get people to universally mask without arresting them or finding them necessarily yeah i mean it really hit me yesterday when i was thinking about this talk about the bath houses being closed in san francisco in 1983. one way is to like shut down all of society and say like no one can have sex and that was not uh and there was places where there was more transmission so that's what happened but actually the behavior change was something that was an individual decision that needed to be made which was how people had sex and condoms and so forth i think we have to think about harm reduction in this case you can't yell at people i actually don't i totally agree with london breed when she said please don't yell at fellow san franciscans i think we have to think about harm reduction 80 percent of the population masking but closing down all society is the most blunt instrument you could get to how to stop a respiratory virus and this is requiring us to each make our own decisions in doing this and so i think if we think where it's protecting ourselves maybe we can persuade people who have been against it to do it and the other thing is i think people have to model it like politicians and you know trump got it let's move on to mike uh michael edmond uh going to speak to us about uh masking and uh and face shields and uh how he and his colleagues are thinking about this in iowa thank you bob it's a pleasure to be with all of you today uh and to talk a little bit here about face shields next slide i i think i can honestly say that uh before uh march 1st of this year i probably had not thought about face shields for more than 30 seconds even as spending an entire career in hospital epidemiology but what happened for us was we admitted our first covet patient at the university of iowa on march the 9th and and one of the things we did as we were preparing for covid to come and when covet actually did come is to really critically look at our supply of uh ppe all of our inventory and what became very clear is that on the surface we had what appeared to be a lot of medical great face masks uh a couple of million but when we started to do projections as to how many we might use and how long the outbreak might last knowing that the supply chain had been severely disrupted because the factories in china had been shut down we became quite nervous that if we did not get any additional supply we wouldn't make it through the outbreak with enough face mask and nor would we with n95s we had even fewer n95s than medical masks and i had some sleepless nights worrying about would we face the time when we'd have healthcare workers caring for cova cases with nothing on their face so we started to think about whether we might be able to to source face shields and interestingly because that supply chain wasn't disrupted they're used in other industries we were able to procure them and so um on march 18th we began supplying all of the people in our hospital with face shields we prioritized clinical workers first but within about a three week period we had every person in our buildings uh in facials including people who do not do uh any kind of clinical care so uh for that uh that was our next step was to have face shields on everybody we you we had masks and n95s available for people that were seeing patients that were either confirmed or suspect uh covered um then we did uh run into some some luck and we were able to procure more face masks our inventory uh improved dramatically and then we added uh medical masks for uh the care not only of covid patients but for all clinical care for all of our health care workers and then we continue to wear face shields uh uh universally uh throughout our institution uh and again including people who do not do clinical work next slide so facials are really a very simple device there's essentially three pieces to them uh the visor is the clear part that that surrounds your face uh which is attached to the frame um and then they have a suspension and some sometimes the suspensions are more complicated and have knobs in which you can uh tighten the uh the fit of the facial sometimes those are just a plain elastic band next slide so the optimal design of a face shield what is that you if you're going to wear one you would want on the anterior surface for the facial to come below the level of your chin laterally you want it to come around your face and extend about to where your ear begins and also you don't want a gap between your forehead and the visor some of the early 3d printed shields did have a big gap there so that i think is a problem because droplets could come down onto your face and then there needs to be enough clearance so that you can wear your mask or a respirator um or glasses um and there are even face shields now that are designed that have a uh bigger space um between your face and the visor so that people can wear lubes for example next slide there are really many different face shields that are now on the market on my blog i've tried to aggregate the various websites i think have 90 different websites where you can order uh face shields on the left you see what is more typical of an industrial type face shield and this is actually what we've used mostly in the hospital because uh early in the outbreak that's what we could get um in the middle there is is sort of a more medical type face shield um as well as on the right this is one of the newer ones that's been developed uh interestingly there are no national standards for the characteristics of a face shield and that is somewhat problematic and as we see when you start to look at the literature on studies that have been done in face shields you might not know whether this was a shield that provided really good coverage going all the way back to the ears or whether it was really just in the front of the face and and that that continues to be a problem next slide um this is a face shield uh it's an interesting one that's developed by some some people at harvard uh and it's shown here on the left in an opaque version just so that you can see the shape of it uh what's interesting about this particular one is the coverage extends underneath of your chip which i think is quite nice and i actually wore it last weekend that's a picture of me uh when i was making rounds uh at the hospital so the coverage of the shield is is highly variable depend on the model that you have next slide and then there's other ones there are shields that are made to attach to baseball caps um there are shields that are made specifically for kids that are fun ones uh that will encourage them to wear them next slide and there's even very special ones like if you're a devo fan uh they have the uh the dome shield uh available for you that you can order online for i think 48.95 next slide uh and then there's also these which i don't consider to be face shields but if you read the facial literature these are often considered to be face shields and you've probably seen these they're often used in operating rooms uh these are surgical masks that have an integrated visor next slide so facials do have a number of advantages um many people find that they're more comfortable they're not as hot as a face mask or generally a lot of people will feel less claustrophobic than when they're wearing a face mask uh and they don't have any impact on breathing resistance uh another great thing is that you can easily disinfect them you can just wipe them off for people and we've heard from a number of people who are hearing impaired they have a lot of problems when people wear face masks because they depend on seeing people's lips to understand speech and i think less patient anxiety when people are in shields as opposed to masks um they protect your eyes which is really important that masks don't do that and they also keep you from touching your face there are some disadvantages some some of them are optical sometimes you get glare um if you're doing you know certain procedures where you really need to have visual clarity you may have some issues there sometimes there can be fogging although a lot of them are now made with anti-fogging properties the industrial ones are bulky they're kind of heavy some people get neck pain when they wear them for long periods of time but they do have a peripheral fit that is uh not as tight as a face mask obviously next slide so once we got everybody in the hospital in a face shield one of the things i started to think about and this was that in early april was maybe we should think about getting face shields out into the community um and so um this was a jama viewpoint that i wrote with dan diekema and eli perinovitch here at iowa and so we uh we hypothesized that if you could have universal adoption of face shields in addition to the other things like testing contact tracing hand hygiene etc you could drive the are not less than one and the outbreak would end um and we we uh based this on the fact that what we were seeing in the epidemiology of this disease is that the primary driver appears to be droplet transmission um the one thing of course that hasn't been done is that we don't know how well face shields work for source control um and and as you'll see there haven't been lots of studies done uh on face shields but clearly they do provide protection from droplets how well they protect on the other side as a source control we don't yet know next slide this uh viewpoint was published this week in jama by mike columbus and colleagues at harvard um and this gets to the core of the debate that's been going on about whether this is a drop of transmitted disease or an aerosol transmitted disease and i think most of us accept that there are going to be cases of both but i think a lot of what we are talking about is what's the predominant mode of how this disease is being transmitted and the breakout quote there i think is important um he says that demonstrating that speaking and coughing can generate aerosols or that it's possible to recover viral rna from the air doesn't prove that you have aerosol-based transmission next slide and his argument about why it's not an aerosol uh primarily aerosol-based transmission for covid um um are there two one is that the uh the basic reproductive number is 2.5 which uh dr milton talked about earlier that's not consistent with other viral respiratory uh illnesses that are transmitted in an aerosol way like measles in which the are not is up to 18 or chicken box and the secondary attack rates are really on the low side so overall it's about five percent um sort of casual interactions like in grocery store something like a half a percent sharing a meal with a person seven percent and then even in households uh you can see that the the attack rate's somewhere between 10 maybe up to 40 but that's not consistent with aerosol diseases like for example chickenpox where prior to vaccine if one kid in a household got chickenpox you could rest assured that pretty much all the rest the kids in that household would get it too next slide so what are the data for face shield so here's what we have these are some simulation experiments that have been done i think the first two are really the only two that are applicable to sort of community type transmission so there is a cough aerosol simulator study that used influenza virus and using an 8.5 uh micron aerosol there was 96 reduction um in uh retrieve retrieval of virus at 18 inches this was a cough that was 18 inches from the person being exposed and 92 at 72 inches and then a smaller aerosol it was 68 reduction at 18 inches another study just used fluorescent dye and sprayed it and this was a five micron spray uh and showed that when a face shield was on a mannequin that there was no contamination of the eyes the nose or the mouth at uh 20 inches the next three studies are really not community type studies these are procedures uh simulations one is a simulated dental procedure one a femoral osteotomy another simulated surgery with a water spray so these would be like things that would be more likely to occur uh in a procedural suite or in the operating room and as you can see for the dental procedure the surgical mask under the shield did get contaminated for the femoral osteotomy um there was eye contamination of the mannequin about 30 of the time and then with the the water spray 40 percent contamination of an inner mask six percent contamination of the face um these obviously in in these types of procedures we would never recommend that a healthcare worker wear a a face shield without mask or a respirator underneath of it next slide there's one observational study um that i could find there was a case control study of nurses that was done in hong kong large hospital in hong kong and what they found was that it the nurses who wore face shields during aerosol generating procedures were protected against developing influenza-like illness um uh compared to those that just wore a face mask um and it was a pretty significant reduction with an odds ratio of 0.12 next slide and then um the the last study that i'll show and i won't review because this is dr milton's study that he talked about but this was the human challenge transmission study with influenza virus um and as you can see uh one group had face shields hand hygiene and no face touching so uh we're we're looking at whether there could be aerosol transmission the control group didn't have a face shield no hand hygiene and they were allowed to touch their face so this would mimic more like contact and draw the transmission but there were very low infections so you see zero in the intervention group one infection in the control group next slide so really in a nutshell this is what we have we have some data that look at how a shield works uh in a person who's being exposed to an infected source what we don't have data on is how well does a shield work for source control um and we have no data either on a dual dual shield model or a universal shielding model which is what we're arguing for in our jamming viewpoint where both the source and the exposed uh have on a facial we do have now at the university of iowa a cough simulator so we are going to be doing studies looking at these scenarios as well as comparing face shields to face masks next slide so i think that this whole uh controversy about whether it's airborne or whether it's droplet is somewhat driven by the framework through which you look at the issue and i think there's two major frameworks here you have an occupational health fair american a public health framework and in the occupational health framework um the type of work that that people who work in occupational health do they are really uh looking uh at things with a very very low risk tolerance and the goal generally is that you're going to drive the risk to the irreducible minimum and so if you think about um going back to kind of basic epidemiology and thinking about the difference between effectiveness and efficacy they're really focused on efficacy they're looking for how do you provide ideal protection to people and they're looking at it really at an individual level on the other hand in the public health uh framework at a population level we'll generally tolerate more risk than you would at an individual level and the goal at a population level is not to prevent every case of cova that could be prevented the goal is to try to get the r naught less than one and stop the outbreak and so the focus is really on effectiveness and effectiveness answers the question how well does your intervention work in the real world and of course that factors in adherence so for example we could we could say to the general public we want everybody to wear an n95 respirator but i think it's highly unlikely that most people would do it because they're not very comfortable um so so i think effectiveness from a public health standpoint is how we're looking at this and it's really i think much more of a utilitarian perspective as opposed to an individual perspective next slide so in conclusion i think in the hospital setting uh we are using face shields we've been using face shield since the beginning of the covet outbreak at our hospital but those should be used with face masks or in the setting of aerosol generating procedures and 95 respirators in the community on the other hand next slide particularly since we have 25 states now that still have no mass mandate i think the best face covering is the one that people will wear thank you thank you mike that was that was terrific and really thought-provoking uh let me have a couple questions for you and by the way the audience were a little long so we'll go over and go till about uh 120 or so so that 12 or so minutes for uh to bring everybody back um is there any evidence that people will be more likely to wear them has that been studied either in focus groups or in the real world if you gave people the choice if you can wear a face shield or you can wear a mask that people will prefer face shields there are no data that i'm aware of we're doing some surveys of our health care workers to ask about that and asking uh them not just because they're wearing both many of them um how one compares the other but what happens when you leave work and go to the grocery store do you wear a face shield face mask so we should be getting some data on that yeah do you have a sense of what people do they choose one or the other um well i'd say in my own experience when i go to the grocery store in iowa city i i would say we have about uh i'd say 80 to 90 compliance with face coverings in general um so a pretty compliant community um but uh i would say five to ten percent of that is face shields and the rest of space mass okay and here at ucsf health system we are moving to uh mask plus goggles of some eye covering of some sort how do you compare and contrast face shields versus that strategy it sounds like you have mass for for people with direct patient contact it's masks plus face shield so here the question is facial versus goggles that's a secondary i think the one advantage for face shield versus goggles is that the shield protects your mask or your n95 uh from getting droplets on it and then you might potentially contaminate yourself as you touch that but otherwise it protects your eyes and that's that's important okay uh actually let's bring on the others because i'm gonna get to a couple other questions that are probably for everybody to battle around so if uh we can bring on monica and don that would be great and hopefully we've gotten don sound uh trouble shot um maybe i'll stick with you for a second mike but then open it up and particularly interested in how don responds this i i kind of get the public health argument we're not trying to bring it to zero we're trying to bring the community down to make the virus go away but we're all individuals in the community when i go out i want it to be zero i'm over 60 i don't particularly want to get covered so um you know and you and others have said it's it's not primarily aerosol-based it's primarily droplet-based but primarily doesn't mean that it's not aerosol-based at all and i'm wearing this face shield and i've got big spaces around the side of my face and the in the bottom and all the so how do you sort of think that through you know to make people comfortable that um you think about an aerosol it feels like there's this fog and people often likened it to you know cigarette smoke if you could smell it then that's an aerosol you sort of know that it's going to get around a facial you probably know it's going to get around a surgical mask as well but how do you talk through that kind of concern about aerosols yeah so i think uh that question that you just asked and and many of the questions that we've faced both uh in trying to do infection control in the hospital um and also at for the university i'm on a committee that's trying to advise the university about what we're going to do how are we going to protect students and faculty etc you know i think all of those questions come down to what's your risk tolerance and it's a very individual personal thing some people aren't worried about it and others really are and i think that it's you work with the the if you're a physician you work with your patient if your patient has let's say um has had a bone marrow transplant they're highly immunosuppressed you know i would advise that patient they should have an n95 um and and face and eye covering uh when they uh are out in public um in a 20 year old i would think about that that same question differently so to me it's a lot of it is about what the tolerance is for risk got it don i'd love to hear you sort of react to sort of these more clinical presentations as you think about the science of of how the virus spreads uh what are your impressions and maybe particularly address the face shield question well i think that's really interesting you know in the the phantom study that michael had up there for a minute uh you know one of the things we did in the preparing for that was trying to come up with a face shield that didn't reduce aerosol exposure and it was really hard uh we actually had to have one that didn't come around the side of the face and didn't come below the chin so we basically had to cut down and just protect against large droplet or ballistic drop sprays uh and um so so and and i think one of those slides very nicely showed that um that that i think it's the niosh data shows in in their mannequin study about a two-thirds reduction in aerosol exposures now you know one of the things is is is you guys are using the medical terminology i'm using the occupational health and aerobiology aerosol science terminology for an aerosol so for me a lot of what you call droplets are aerosols and there's and then you have in my world there's splash and spray which are uh you know uh we i like to say we are biologists like to argue about whether a cow in a tornado is a bio-aerosol but you know big things that are imparted with momentum from where then they came i don't think of as aerosols i think of that as splash drops and and so that's what face shields are really originally designed around but they are actually protecting against the coarser aerosols and even a little bit as we saw against the fine aerosols so you know i i think we're one of the things i hope comes out of this uh pandemic is that we begin to get our terms straight across medicine and and industrial hygiene because uh you know i i fear that medicine is kind of stuck in this dichotomy that goes back to chapin's 1910 textbook and it hasn't been updated with all this stuff that's been done since 1940 and but so i think we can come to a much more nuanced understanding of this i i definitely think that the stuff about dose response is really important but i also think as part of that is that root of exposure is probably very important too we know that there are anisotropic infections like uh anthrax as a bacterium that's clearly got that uh had no viruses that way in fact the adenovirus vaccine takes advantage of it by giving people a capsule of adenovirus so they get a gi infection and they they don't get sick whereas by inhalation uh even in the army you will have young recruits die of it once in a while so i i think that that we're we're really not that much on a different page as it sounds like sometimes uh and and i think that uh the the universal masking and uh and the face shields are uh something that we can begin looking at uh as we get more data and i'm thinking maybe i should be putting people into my gazoon type machine with the face shields on not just with face masks we are testing people's homemade face masks that they bring with them too it sounds like there is evidence though of conjuctival that is one of i think you mentioned that there are receptors in the eye absolutely yes that makes some sense to be if we can have eye covering um monica part of the evidence that you cited for your theory was the increased rate of asymptomatic infections and part of it was maybe a lower mortality rate in people who are wearing mass but there are there are alternative explanations for both of those uh you know younger people getting infected and other things that we do new medicine you know medicines that are partly effective and proning and all that kind of stuff so how do you dissect that out and be sure that we're not getting faked out and saying it's because of the mass as opposed to other things i actually do think it's multifactorial um uh why we're having low death rates thank god in the city and um and why we the death rates even around the country are not as high i don't think it's exclusively because of us i think that would be a non-nuanced interpretation i think this is partially masking is partially one of the most important things we can do but so is steroids and remedies severe and treatments that are getting better in the last three months so it is what's been so exciting is i don't think i've ever seen anything and i wasn't around at the very beginning of hiv but where things are moving so quickly in terms of progress and how science is informing everything that we should be doing and then i've also been frustrated because politics is informing it more than it should be in this particularly polarized time and we have really good scientific things that have happened in the last four months including the knowledge of something so simple but it requires behavior and um i think combined with all everything put together we can get through this pandemic faster i really believe that so boy if we could get out of this in the next four or six weeks if every single one last that would be amazing yeah we had john barry the author of uh the great influence on a couple weeks ago here and he had an editorial in the times yesterday and the first line i thought was brilliant it was uh when you miss when you mix science and politics you get politics it's the dominant yeah capture things very well um maybe it's both for don and mike you know mike and your role as trying to do infection control and or adventure prevention in your health facility and on from the scientific standpoint or the the more engineering uh view when you talk about ventilation i sort of think ventilation's good and that's why i like being outside and not inside and then don you got me scared that we blow the virus around and instead of it only traveling three or four feet it's now going to travel like a football field and now i'm scared so is ventilation good or bad or is it both and how do you think that through and but then i'd love to hear mike's thinking about that in sort of the healthcare the context of how we organize ourselves in a healthcare system we got asked that same question on the today show this morning i think it was good i feel good about that thank you it can cut both ways so you know ventilation in that engineering lingo means bringing in dilution air it does it means dilution ventilation not just blowing the air around and in that restaurant in guangzhou one of the problems was they had sealed up the exhaust fence and uh you know had they had the exhaust vents there they wouldn't have had the buildup at that end of the room and they might not have had there might have been no story at all uh and so i and i think this is gets to the point of uh of uh how do we um you know why i would like to get this terminology thing straight because it could be droplets that what you would call droplets but they were 10 or 15 microns but they were being suspended in air so they're an aerosol to me that that was involved in that guangzhou restaurant right but that what what uh when i speak of an aerosol i mean something that ventilation would have an impact on that pollution ventilation could help with which is not going to help with a splash or a spray but it will help with stuff that's floating in the air and i think that much of what we're hearing about what is working with with surgical masks or face coverings and with face shields is all talking about the same thing something that ventilation can also help with and which is why the japanese ministry points to uh having uh closed poorly ventilated places crowds and close contact intersecting to be to high risk environments that i think that is it is really confusing because you think about that restaurant and that the air conditions on there's no there's no sort of exhalation valve and it's blowing across the restaurant four tables away it feels like that has to be what we would think of as aerosol it has to be sort of equivalent of smoke as opposed to a droplet a magic droplet flying 15 feet but you're saying that it could be actually a droplet that goes that far well a small droplet that's somewhere in between the two i guess it's probably it's some kind of inhalable probably thoracic fraction or respirable fraction i'm not sure if it's restorable fraction log or it's an aerosol if it's in more a little bit larger you call it a droplet i say it's still an aerosol because it floated on the air that's got it got it mike how do you think about all of this and the role of ventilation and prevention oh i mean obviously in the hospital setting uh when we know that we have uh covered patients we have them in negative pressure rooms um and um but but sometimes patients are you know in a regular room and then they and we make a diagnosis that we might have missed you know as they came in the door or something um and we have to move them but i guess the one sort of consolation to me is that we are really not seeing much in the way of nosocomial transmission within the hospital um and um we are not we we're not using very many uh n95 respirators uh except for when we are doing aerosol generating procedures so so with masks and shields and the ventilation that we have it doesn't seem like we are perpetuating uh the disease inside the hospital yeah um maybe a couple last couple questions um i think for which one of you mentioned phomice maybe don did but it sounds like you know i'm trying to remember back to february or march hard to remember it feels like this feels like dog years but you know we were all just incredibly frantic about touching the mail and touching our nose and touching everything and and you know and and and cleaning our hands every 10 seconds at least the common thinking is it's less important is is that correct or have we just gotten complacent about that now why don't you start with that and maybe take that to others if you want well i mean that's been my sense that you know relaxing on that hasn't seemed to have any impact how do we know i mean we're certainly seeing a ton of new cases so but what what's the evidence that that is a less important route of transmission well i don't know i mean i'm still being very careful with watching my hands you are okay um but because i don't know i i i'm on the precautionary principle i'm gonna just be careful yep all right sounds like your principle's the same as mine mike how do you think about uh phonates well i i would say that my hand hygiene practices are probably at their baseline which are probably higher than the average person but uh yeah i i guess i don't worry much about that uh that and and because if i generally if i'm going to touch something i'm going to probably going to do hand hygiene you know in in in the near future uh i don't i just don't think that that seems to be the dominant mode of transmission um i would say in iowa city the recent cases that we have had um particularly like in the lat and around the beginning of the month they were all uh pretty much young people people under the age of 25 and one common factor was they all had been in bars yeah yeah um one thing i went talking in a college town but thank you you should have warned me that that was coming uh monica go ahead sorry i was just gonna say that we i think the reason we even thought of phomites is because we just couldn't figure out what was going on at the beginning and it's actually very clear what's going on um you shed this at high rates even when you feel well and that asymptomatic transmission from the nose and mouth i think really speaks to the epidemiology of spread and that is different that's different than sars that's different than influenza that's different than many viruses where you feel unwell when you spread it and so um i think the fomite surface issue i'm not very concerned about and i like you i wash my hands as much as an infectious disease doctor does which is a lot great so maybe last question for i'd love to hear mike what's going on in iowa city are you seeing a surge and and kind of what's the political environment around prevention there as well sure so we did uh we did see uh an increase in cases uh sort of at the uh probably around the last week of june um that has now seemed to quiet down um the the issue in iowa which you probably are aware of um is uh the meatpacking industry as a big driver of the number of cases um and uh prisons um congregate settings really when people are are densely packed together uh you start to see lots of cases and i think we have been a great example of that uh politically we don't uh in iowa have um a mass mandate or much of any other kind of mandate um and um i do think if we could uh do better with that we could probably get these uh our infection rates down but right now our infection rates continue to increase in iowa yeah and monica what what are you uh i'm struck by the same thing you mentioned which is i have it's pretty impressive when i walk around i may be walking only in certain neighborhoods but people do seem to be wearing masks a lot and yet we're seeing a moderately impressive surge not houston or miami or phoenix but but real uh how do you how do you process that yes i mean i don't think masks prevent it completely i think that when people mingle masks may lead to lower rates of severe illness but don't prevent it completely which really puts all together these three talks right like that um that no one's wandering around with um like whatever they wear in contagion in those movies like we have masks and mass filter out the majority of viral particles so as we open up and as other places have opened up there have been cases and um that has been seen here and what has been a big relief has been the low death rate um here and many other places and that was seen in the czech republic and everywhere else they would see the cases um back off as we have here but not see the increase in deaths and i think that's what's hopeful about the mass wearing in conjunction with cases last question don you were talking about airplane flight and the the audio was bad but sounded like you were talking about how the the sort of swirl that comes up from the people and down from the ventilation system and it's it's sort of bad but i think a lot of people are trying to decide whether to fly and after hearing the three of you i guess i'm not sure i'm closer to what the right decision is so take us through that for a second and then i'd love to hear whether mike and monica would fly this summer well i'm waiting for the general rate in the population in the country to go down before i could run an airplane i mean i i am trying to be extremely safe because my father who's 102 is still living alone with his wife and he's taken care of and uh and i'm trying to stay safe so that i can visit him safely yeah and so i am being super cautious about a lot of things um and in airplanes the the you know you have the gaspers and you have the air flowing down over your body but the heat plume from your body is trying to go up so hopefully eventually airplanes will be redesigned so the air goes up because that's the way it wants to go then you have plug flow and you would have much less exposure because now when you're pushing it down and it's trying to go up it goes sideways and that's the problem so um yeah and and here in maryland in college park we're in prince george's county the hottest county in the state of maryland and just west of the campus is a zip code where 80 of the people are non-citizens and has the highest tax rate in the state cumulative attack rate is about 5 at this point in that zip code so we have a lot of problems here and in the state although among people over 65 the new case rate is dropping rapidly it is rising rapidly under 35 units you're really worried about who else is going to be on the plane and the increased probability that there's somebody who's going to be infected on the plane yeah uh uh mike do you want to take that would you fly yeah well i actually was on a plane uh a couple of weeks ago um i wore an n95 um the flights were for the most part not very crowded and unlocked and and face shield or just i had my face shield with me i did not put it on because there was no one within six feet of me um and in one of my flights i was the only passenger it's reasonably safe beyond the incubation period so i did not get covey all right good and monica last word yes i would i would fly and again you're you're getting everyone's individual biases and they're anywhere you can do to everyone's tolerance so yes i would fly with the mask i believe in the mask got it okay thank you all really grateful it's a really complicated but uh extraordinarily important discussion and topic and i think you cleared up a whole bunch of it and there are areas that just aren't clear until the science gets better so thank you thank you all for that uh thank you all for watching and listening you see hopefully on the screen our our wonderful production team who brings these to you each week and i thank all of them and we'll be back next week i'm not quite sure what we'll talk about but there will be something and we'll continue doing this until this is all better thanks so much have a great week stay safe

Channel: UCSF School of Medicine

Views: 1,035,336

Keywords: ucsf med school, ucsf medical school, university of california san francisco, med ed, ucsf medical student, uc san francisco school of medicine, doctors, physicians, ucsf, medical education channel

Id: Cio3rh6ta3w

Length: 89min 38sec (5378 seconds)

Published: Thu Jul 16 2020

Reddit Comments

[u/drbbton]

An hour and a half? Can we get a TLDW?