As we continue to navigate these unprecedented times, KCBS Radio is getting the answers to your questions about the coronavirus pandemic and the issues that have arisen around it. Every morning at 9:20 a.m. Monday-Friday we're doing an "Ask An Expert" segment with a focus on a different aspect of this situation each day.
Today we're looking at the virus itself with Dr. Bob Wachter, chair of the UCSF Department of Medicine, who has joined us for previous "Ask An Expert" segments.
Dr. Wachter, good morning. Did you get that golf game in?
I did, it was glorious. I was no good but it was glorious.
Being bad never felt so good right?
Exactly.
Let's get started, I have a couple of quick questions for you myself and one of them is focused on a topic we have addressed, which is this much discussed antibody study that Stanford researchers have done. They've now changed the numbers a bit, gone back and done some readjusting of the analysis and are now determining a new - I'd guess you'd call it a hidden number of coronavirus infections they believe were extant in Santa Clara County at the time that they ran these antibody tests on about 3,000 people.
Yeah we're seeing a lot of these antibody tests come out. I think the Santa Clara one from Stanford was the first and it came up with an estimate that was very different than most of the others so it got a lot of notice. I kinda prefer to look at the totality of them because we've now seen them from several cities in Europe, from Miami, New York. And the best number seems to be that if you take the number of diagnosed COVID cases - who have had a positive test - multiply that by 10-15x, that's probably the number of true cases.
Part of that was that people who were diagnosed early or had COVID early probably didn't get tested, some people just stayed home. And so the Santa Clara study that Stanford did came up with a number more like 50x, and I think most experts still believe that the sampling methods - some of the more arcane methodological issues - make that a little bit less credible. So the best estimate I think is that if we think that, for example, in San Francisco there have been 1,500-2,000 diagnosed cases, the number of actual people who have had COVID is something at like 10-15x that.
So that would put the Bay Area at around 100,000 cases, 10,000 of which we know about and more that we don't.
Yeah and you can take those numbers as either good news or bad news. The good news is if that number is much larger, meaning a lot of people had it and didn't know about it, obviously all those people did well and no one died, so it lowers the mortality rate. On the other hand it makes clear that the virus is pretty stealthy and there's a lot of asymptomatic or mildly symptomatic people out there. And that makes the whole concept of catching cases and tracking contacts and keeping ourselves safe from future surges even more difficult.
So that leads to one more question and that's this Major League Baseball study which took a pretty good-sized sample of ballplayers and people who work for the ball clubs and all that and came back with some fairly low numbers - I think they had 5,700 people and found that the rate of people with antibodies was lower than might have been expected. Your read on that?
Yeah it's a very low number, I forget the number but it's well less than 1%.
Right, I think about 0.7%.
Yeah I think what we're going to find is that in places like New York, Detroit and Boston that got hammered, you're going to see numbers of people that had antibodies in the order of 10%. 15% maybe in New York and maybe in some of the hardest hit areas of New York City even 20%.
For the rest of the country - and certainly this is true of the Bay Area - I think the best guess is going to be about 1% of people have had the virus, have developed antibodies to it. We're still not 100% sure if those antibodies are protective, but I'm more than 90% sure that they're going to turn out to be. What that means is that if 1% of us have had COVID and we are protected from recurring, 99% of us are exactly the same way we were three months ago. And there's nothing that has changed about the virus, despite some of the chatter you hear about mutation. The virus is still the virus.
So that's why all of the steps that we're talking about in terms of opening, doing it very very carefully and thoughtfully and testing and contact tracing are critically important. If you go to a place like New York where you start seeing 20% or thereabouts who have already had the infection - and presumably I do believe we'll find out are immune to it, at least for a while - that changes the dynamic a little bit. Those people are unlikely to become reinfected and will potentially have more freedom of movement. But in the Bay Area and even throughout all of California, I think we're going to be talking about 1 in 100, maybe at most 2 out of 100 who have had the virus and have antibodies.
Ok let's get to the questions from our listeners, they've been sending these in at askus@kcbsradio.com.
I've been hearing a lot of reopening proposals that involve wearing masks. How effective is wearing the same mask on say, a cross-country flight that lasts several hours? Don't masks get moist after extended wear and become less effective?
Yeah, if they get truly moist then they do become somewhat less effective. But in the hospital we generally get masks at the beginning of the day and we will wear the masks most of the day. If it really gets wet then it becomes ineffective but from the purposes of putting a mask on at SFO and wearing it until you land at Newark, that's perfectly fine.
Is someone infectious before that person tests positive for COVID-19? If so, for how long? For example, would very frequent testing with quick results reduce or eliminate the spread of the virus or the need for contact tracing?
It's a great question and the usual question is, is someone infectious and contagious before they have symptoms? And we know the answer to that is absolutely yes. That's really one of the superpowers of this virus - you can feel perfectly fine and yet it is in you and you are capable of transmitting it.
The question of syncing that issue up with testing is complicated and I don't think we absolutely know the answer to it. People can have false negative tests. The tests are pretty good, but early on in the infection you can have false negative tests. And assuming the technique was good - meaning they swabbed you the right way and they handled the samples the right way - one would presume that the fact that you're false negative means that you have very low virus, meaning you are less contagious than you will be when the test is positive. In other words, the test result should be somewhat correlated to your degree of infectiousness. But I would say that that's probably not perfect. Meaning there probably are people every now and then whose test is negative and yet they have a decent amount of virus and they are infectious. And that's yet another sobering thing about the virus.
What we do think though, is that the testing strategy is very important. The most reassuring thing you can know about someone - for example someone coming in to the workplace or into a restaurant or getting on a plane - is if you knew for sure their test was negative that day. I think it's reasonable to presume that they have a very very low likelihood of both having the virus, and if they did have it, having enough that they are infectious.
We're a long way from being able to test people in that way, meaning a rapid test that you can get back in 15 or 20 minutes that you might do everyday or every few days. We're moving in that direction with the recent approval of both saliva sampling as opposed to nasal swabs - an easier way of collecting the samples - and then a new antigen test that was just approved a couple of days ago by the FDA, which is an easier and faster and cheaper method than the one we've been using so far. So we may be getting to the point where we actually can, without that much hassle, test people - everyday is a stretch - but maybe every 3-4 days. And Governor Cuomo in New York just required that every worker in nursing homes gets tested twice a week. And that's actually a reasonable thing if you're looking at a very high risk population like nursing home residents.
If I get tested negative can I volunteer somewhere? It seems silly for healthy people to feel helpless in regards to cheering up potentially lonesome people.
Can I volunteer meaning going into a high risk place like a nursing home? The problem with the testing again gets back to the last answer. Assuming we're talking about a virus test - again the key distinction here is are you testing for the active virus or are you testing for the antibodies, which means you had the virus in the past and your body has mounted a response. If we're talking about the virus testing, we're all going to have to figure out how to ensure that people don't have the virus if they're going to go in to high risk areas. And the highest risk area is a nursing home. So if someone wanted to volunteer in a nursing home or even work in a nursing home, I think it is reasonable for us to think about testing those people before they go in whether you're a volunteer or you work there.
The antibody testing - assuming the test is accurate - once you have the antibodies, the antibodies will last at least for many months, maybe years. We don't know the answer to that yet. The virus test, it's sort of like a pregnancy test. You know the person doesn't have it today, you don't really know the person doesn't have it next week. So the fact that you had a negative virus test two weeks ago gives us very little reassurance that you're safe now. Particularly as the tests get better and faster and cheaper, I think we are going to be moving towards just-in-time testing in certain circumstances. If you're going to go into a nursing home or maybe even visit a patient in a hospital you may need to get a test within a day or two of that.
At UCSF we are testing all of our hospitalized patients when they come in and we're also testing all patients within a couple of days of having a procedure or a surgery. That actually has less to do with infection control and more to do with, if you have the virus in you and it's brewing and we're about to do a major surgery on you, we want to know that because it might be the wise call to delay it until you're better.
I'm sorry, but I still haven't heard a good explanation for this particular mask question. If my face mask can keep my germs in, why can't it keep other people's germs out?
(laughs) It's actually a terrific question and it has to do with the dynamics of what happens when we breathe, cough, sing or sneeze. We create a forced airflow out of our mouth and if it hits a wall, and the wall is the mask, it prevents it from spraying out three, four, five feet in front of us. And so it does not prevent it from spraying out. If you coughed or sneezed into a surgical mask - and you see the holes on the sides and above your nose and below your chin - it's obvious that it will get out, but it gets out in a spray that's markedly muted. It gets out to the side and down and up, not out in front of you.
On the other hand if we're talking about a few particles in the air and you're wearing a surgical mask, which is relatively loose-fitting and has space around it and is actually even a tiny bit porous, then it's not that much protection against you breathing in a particle that happens to be in the air. So really it's greatest level of protection is because the wearer is no longer capable of sending a spray of particles with virus out into the air.
Now the industrial grade masks you hear about - the N95 masks - the material is very different. It's much thicker and they are fitted around your face, which is why it's hard to wear them for long periods of time. It's kinda tough to breathe because they actually are limiting the amount of stuff that comes in as well as the amount of stuff that goes out.
I hear a lot about virus particles. How many does it take to get me sick, and how big are they?
They're tiny. None of us can see them, which is part of the problem.
It's a really interesting question. I've forgotten the number exactly but it's in the hundreds or thousands of particles, which people always find mind-blowing. Here's this virus, and you think that one particle is enough if it gets in my eye or the surfaces it wants to go to to begin replicating, which are what we call the mucosa, meaning the inner lining of your nose or the lining of your eye or the back of your throat. So it's sort of logical to believe if just one of those little buggers gets in there, it's going to start making its little viral factories and the next thing you know you have COVID. It just turns out that not only from COVID but from studying other infections over the last 100 years, it doesn't work that way. You actually need a big dose of the infection to get in you - hundreds or thousands of copies of the virus in order to be at risk.
Which is why just passing by somebody in the Safeway or walking down the street and someone is jogging eight feet away from you is of essentially no risk. It's why when we do contact tracing, we don't try to figure out everybody who is in Whole Foods at the time you were there. We try to look for people who spent at least 10 minutes in close proximity to you, because there is a dose effect. You need a bunch of virus to get in in order for the virus to take root and cause infection.
Do we yet know whether or not SARS-CoV-2 can be transferred via mosquito bites?
The answer seems to be no. The world of infections tends to divide itself into several different routes of transmission. There are some that are in the blood and that's classically malaria, which can be carried by one organism that gets it from blood and then injects it into somebody else. There are others that are transferred by the fecal-oral route, meaning it's in your stool. But the viruses that make up the common cold, the flu and are the coronaviruses are transferred only through the respiratory route. They come out of your mouth or nose, they have to take root in the back of your nose or your throat in order to cause infection. So the amount of virus in the blood is actually very, very small and we're quite sure that it's not going to be mosquito-borne. It comes through touching surfaces that have it and then touching your eye or face or getting a big dose coughed on you or sneezed on you.
I think Governor Cuomo mentioned about two-thirds of New York's cases, they believed, were among people who were sheltering in place - in other words, not going to work. And the question here is, do we know definitively whether anyone has contracted the virus through grocery shopping or ordering take-out or while strictly adhering to shelter-in-place orders?
It's sort of a math problem. I don't think we know for sure that no one in history has contracted the virus from touching a surface like a shopping bag. But what we do know is that in order for that to happen the virus would have to be on the shopping bag in fairly large doses. It probably would have to be within a recent period of time that the virus got there because we know the virus can last a couple of days when it's on a smooth metal surface, but when it's on more rougher surfaces like paper, it doesn't last very long - several hours. And so I don't think it's been proven that that has never happened, but shopping bags and things like that are very low risk. For me, when we do shop we bring the shopping bags in, we put them on the floor, we're careful about taking things out, we will clean the outside of the bag. I think that's a prudent thing to do.
In terms of sheltering in place, it sort of depends on what's happening in the place. So certainly people have sheltered in place and gotten it if a family member, for example, has come in and been infected and then people in the family have gotten infected. But if you truly are staying away from other people, then your risk is zero. There sort of is no way to get this thing unless the virus is introduced into your environment or you go out of your environment. So if you were sheltering in place, that is the safest thing you can possibly do.
I have an upcoming hearing test. How is it safe to be in a small booth with lack of social distancing?
I'd have to know more about the booth. I do worry about the booth as a place where if there's a virus in there, it can probably linger in the air for a while. So you'd want to know for sure how the booth is cleaned. You would want that booth to be sterilized to the degree possible when you went in. I think it'd be also prudent to wear a mask and be sure everybody around you is wearing a mask.
I'm in remission from stage four colon and lung cancer thanks to the great care I received from UCSF. My last chemo was seven years ago, do I still have a compromised immune system?
No. Chemo only lasts for a while in terms of lowering your immune system. First of all, congratulations and I'm glad to hear things went well with us.
Seven years out you are virtually certainly cured of the disease, so in terms of the risk from the cancer that would seem to be extraordinarily low. In terms of the chemo, the suppression of the immune system is often on the order of weeks, maybe a month. So seven years out, it's like you never got it.
What are your thoughts on hemoperfusion devices that remove the virus and inflammatory markers from the blood?
Don't know enough about them to say anything intelligent. It's certainly not been studied as something that's proven to be valuable.
Would a cardiac arrhythmia premature ventricular contractions be considered an underlying medical condition in regards to possible complications?
Well premature ventricular contractions are a benign cardiac arrhythmia. Almost everybody has that. If you drink a little too much coffee you may have that. So it really depends on what the cardiac arrhythmia is. In general, the kinds of medical risk factors in terms of when we talk about pre-existing medical conditions that put you at increased risk, that wouldn't be one of them. I think in terms of cardiac conditions I'd look at someone who had significant arrhythmias, meaning life-threatening arrhythmias or more commonly a prior history of a heart attack or a history of heart failure would be the ones that I'd particularly worry about. Not premature ventricular contractions.
I'm concerned about going to a restaurant if that becomes possible. Could the virus be transmitted on food or plates or glasses if the cook or server has it on their hands or is not wearing a mask? What should restaurant staff do?
Restaurants are going to be tricky. Walking into a workplace or supermarket, you sorta want everybody having their masks on. Not only the workers but the customers as well. In a restaurant you can't do that as the customer. So what can the restaurants do? Every restaurant in the country is going to try to figure this out. The tables need to be six feet apart. Certainly I would think the waitstaff and the cooks and all that should be masked. Single use menus, not sharing, things like that.
In terms of could there be virus on things like plates and utensils? If they're not being careful, if they're not washed, the answer is yes. And one of the things we worry about is somebody coughs on their hand, touches something - particularly a plate that's a smooth shiny surface - and then someone else touches it. So we're going to have to be really sure the restaurants have done all the right things before people will be comfortable going in.
I know you wanted to pay attention to a website that some of your students at UCSF have put together. It's really great, this is the one that looks at common myths.
Yeah, the medical students at UCSF came together. They've been spectacular because many of them are not able to come into work, and the ones who have have run blood drives and done volunteer work collecting masks in the early days.
One of the things they just did was put together a website on common myths. First of all it's in seven languages, which is wonderful. And it has all the questions - very similar to the kinds of questions we've done: can I get COVID from this or that or from a mosquito or from shopping. And so it's definitely worth looking at.
We've got that here, it's covid19factcheck.com. Dr. Wachter, thanks as always.
Thanks for having me.
