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 holding a broad conversation about the spread of the disease with Dr. Arthur Reingold, epidemiologist and UC Berkeley professor of public health.
Dr. Reingold, you were here on the very first of these "Ask An Expert" segments we did, and now see what it's turned into. Thanks for coming back with us again. How are you?
I'm always happy to help.
Let's just tackle these. I have a long list today ranging from the specific to broader questions about epidemiology and how we understand all the information that's flowing our way.
First one: my roommate is getting what seems like multiple shipments from Amazon everyday. How should we be handling these when they get to our house? She leaves them untouched at the front door for two days, I tend to wipe them down and open them immediately. What's best?
I think either of those approaches can increase safety. Studies show that this virus doesn't survive on packaging, paper or cardboard for more than a few hours. So I think that if you want to bring it in right away because you're worried about it walking off or need it right away, wiping it down is certainly reasonable. Or you can let it sit there for a day or two. I think either of those approaches can be highly effective.
This one is related but it speaks to the fact that so many households have somebody going out to work and somebody not. How much wiping down of surfaces should roommates be doing when two are working from home and one is still going to work because they're an essential worker?
I think fundamentally what it means is that the chance of the person who has to be out and about for work could bring the virus home and still be asymptomatic and share the virus. It just means that the things we have told people for some time now need to be followed as closely as possible and clearly, decontaminating surfaces, good hand washing, good respiratory hygiene, these are things people should be pretty familiar with now. But it means in that circumstance you need to be more attentive than you might need to be if you didn't have someone coming in and out of the household all the time.
UC Berkeley is doing a study that includes several cities in the East Bay. The study includes both antibody and virus tests. I think there is a 70% accuracy for the virus test, giving 30% false positive or negative. What are the lower detection limits for these tests and how they are interpreted?
So that's a really complicated set of not just one question but multiple questions. The antibody test is really very much an experimental tool. The hope is that that provides evidence of prior infection and perhaps immunity for some period of time, but many of those tests may not be terribly good. Others require validation.
With regard to the PCR test, the test where you take a swab from the nose or the mouth or the throat, increasingly those tests have better accuracy than in those early estimates. The tests are getting better and better. We do know that there are what we call "false positives" where somebody doesn't really have the virus but has a positive test, but perhaps the bigger concern is that some people who do have the virus have a negative test. That's what we call a "false negative."
I would say that those are important considerations in interpreting test results but I don't think they should be an impediment to using these tests to guide public health action or to use them in research.
This next question I could have written, but I didn't. I keep hearing about sensitivity and specificity and I have trouble keeping the two straight. Do you have a way for me to remember?
Sensitivity basically asks the question, of the people who truly have the disease or the infection, what proportion will have a positive test? And of course we'd like that to be 100% but even for the very best tests it's typically not 100%. And of course you could be truly negative today and then positive tomorrow so even if the test is perfect it doesn't necessarily predict what'll happen to you in a day or two.
Specificity is, of all the people who truly don't have the disease or infection, what proportion will have a negative test? How to keep the two apart, or keep them in your mind - I guess I've been talking about these things so long that for me it's second nature but I don't have a good short hand.
Ok fair enough, we'll all have to study a little harder in our graduate level classes.
There is a great deal of talk now about a second wave. What are the circumstances of a second wave? The triggers? Likely locations?
So the concept of a second wave largely comes from the flu pandemic of 1918, when a novel influenza virus - it's a different virus to be sure - first struck in the spring of 1918 and caused a wave of illness and death. And then it went away for the summer as influenza viruses typically do, and then the following fall and winter there was an enormous second wave, much much bigger than that first wave the prior spring.
So people are concerned that even if there's some seasonal reduction because of warmer temperatures, even if we do a good job of sheltering in place and social distancing and the like, that if we see a dimunition in cases this summer, then we could easily see a much bigger second wave of cases in the fall and the winter. Because first of all, we think the virus will still be circulating. And secondly, most people in the population will still be fully susceptible until we have a vaccine to give people.
How and when did the 1918 "Spanish Flu" pandemic end? Is that virus gone or is it still a threat to humans? What are the implications for our current pandemic?
So the 1918/1919 flu pandemic which caused a tremendous death toll around the world probably ended as a result of killing a lot of people, and most other people becoming infected and surviving. So it was probably a result of herd immunity, and basically the virus no longer being able to circulate in a population where most people were immune.
The descendants of that influenza virus, if you will, are still with us. But that's because the influenza virus is constantly evolving, changing antigenic material and the like. We certainly don't have the exact same virus circulating now, because the pandemic of 1918.
If somebody is an asymptomatic carrier do they recover and develop antibodies? Do they cease being transmitters or could they be like Typhoid Mary and continue infecting others unwittingly?
So we don't have any evidence that people remain chronically infective with the COVID-19 virus in terms of how "Typhoid Mary," if you will, remained infective with typhoid for decades. And that has to do with that organism living in the gallbladder and being shed in the stool. People can be carriers of typhoid for literally their entire lives.
We don't think that happens for this virus. How long you can stay infected and potentially transmit it to others is an unanswered research question. We think at least a couple of weeks. Whether it can be substantially longer than that, I think we need more information.
We keep hearing these reports about that model from the University of Washington calling for more COVID-19 deaths. Can you explain how these models work and how much verification there is of their assumptions?
So the first thing to say is that this is sort of a commonly held view - all models are wrong, some models are useful.
And so everyone agrees that a model is only as good as the assumptions you build into it. The University of Washington has an extremely sophisticated group of modelers who are quite good at what they do. But if the assumptions in the model change, then the results of the model will also change. For example, as I understand the most recent change to their model predicts more deaths from COVID-19 occurring in the United States than they projected not very long ago, basically because the assumptions in the model changed. Primarily, in the area of people doing less sheltering in place as restrictions are loosened and people perhaps don't follow even basic hygiene measures that'll have increased transmission of the virus and therefore increased cases and therefore increased deaths. But all of these assumptions, as they go into the model, are just that - they're assumptions.
How long does virus stay around on surfaces? My son-in-law and his girlfriend want to stay in my vacation cabin for the weekend. I need to know how many days to stay away from the cabin for all the virus, on all surfaces, to be gone?
Well as I alluded to before, the virus doesn't seem to persist on paper, cardboard and surfaces like that for more than few hours; six to eight hours at the most. On metal surfaces and plastic it seems to persist longer, potentially for up to a couple of days depending on what type of metal it is.
So certainly if one is gone from the house for a week or two, my assumption is the virus would no longer be present. But it wouldn't be unreasonable to do some cleaning of surfaces before reoccupying the house if you're worried about it.
Please talk about herd immunity. What can herd immunity do for us?
Well herd immunity is the basic notion that an infectious agent can't continue to be transmitted in a population where most people are immune. And so therefore, just to take a simple example, if I am susceptible to getting measles or chicken pox but everybody around me is fully immune to measles or chicken pox, then my chance of coming in contact with measles or chicken pox is zero, or very close to zero. So I benefit from the herd being immune even though I myself am fully susceptible. So it's a form of indirect protection against infection.
It's particularly important in terms of why we use vaccines for measles for example, because we have people who cannot receive a vaccine because they have leukemia or some other cancer or something like that, or they won't respond to the vaccine. We can still protect them if everybody around them is vaccinated and immune.
Are we losing our immunity by sheltering in place?
I guess it depends on what you mean by immunity, to coronavirus or if you mean to other viruses. But I have heard a concern that if we all shelter in place long enough, our immunity to other infectious agents as a population may go down because we're not being exposed to and infected with other infectious agents. I'm not too worried about that.
There's lots of talk about asymptomatic or presymptomatic athletes "shedding" the virus in the kind of close contact that these guys have on the field. What exactly does "shedding" mean and how does this transmit the virus? Only by contact or through the air, both?
Well "shedding" simply refers to the fact that the virus is present, for example in the secretions coming from your nose or your throat. It could be in other parts of the body in terms of sexually transmitted infections. But basically, saying the virus or infectious agent is present and then if those secretions may get to someone else in a part of the body where the virus can be transmitted, that shedding by one person can result in transmitting the virus to the other person. So that's really all shedding means.
The CDC recommends hydrogen peroxide as a product that can kill COVID-19. I have regularly used one cup of hydrogen peroxide to one gallon of water in a humidifier in my bedroom to kill dust mites and pollen. Why wouldn't prisons, nursing homes, group homes, etc. be able to use a humidifier in every room with hydrogen peroxide and water to mitigate the effect of the virus particles in the air?
I don't think that would work to reduce the virus particles in the air. When you're putting something like a disinfectant into a machine like that, what you're primarily trying to do is prevent any build-up of bacteria - perhaps fungi - in the reservoir that's being used to create a mist or some kind of cleaner or cooler or drier air in the room. And you don't want to be spraying bacteria or virus into the air from that machine. So the disinfectant in the machine is intended to prevent a build-up of those organisms in the machine, and prevent the machine from putting out a mist of those organisms. But it really is not an effective way to preventing me from transmitting the virus to you through the air. It won't work for that.
How confident are you that an effective COVID-19 vaccine will be tested and certified as safe within two years? Four years? Ever?
I have no way to guess. People who I know and respect are quite optimistic that it'll be possible to develop a COVID-19 vaccine, but most think it'll be at least 18-24 months before we have such a vaccine of proven efficacy and safety available for widespread use in the population.
How will testing and tracing work? In the time it takes to get a test result, someone might get infected. Do we need daily testing? Twice daily?
Well I think that's a great question, and I know of organizations that are trying to test everybody weekly or monthly or something like that. That obviously comes at substantial cost and a lot of bureaucratic organizing to test large numbers of people on a regular basis. I think one does have to think carefully about what the reason is for doing that and what populations would benefit.
So just to think as an example, that might be really important to do in terms of staff working in a nursing home or some congregate care facility where we really don't want to introduce the virus to people living there. In some instances that might make a lot of sense. But I'm a little skeptical that testing large numbers of asymptomatic people in the general population on a regular basis is going to turn out to be a terribly effective strategy.
This same questioner goes on then: how do we reconcile frequent swabbing, which is in itself a DNA collection, with our strict health privacy laws and regulations?
Well I don't think that's a particular problem. We have public health laws in California and every state that dictate privacy of people's personal health information, and federal laws about that as well. But we also have exceptions for public health. And so certain types of infections are legally reportable to the health department and follow-up is legally mandated.
So just to take as an example, if I have tuberculosis my case must be reported to the health department by the laboratory or the healthcare provider and they have the legal right and responsibility and obligation to trace my contacts and see if anyone else is at risk of getting tuberculosis. Same thing is true for COVID-19. But the health departments have the authority to protect that information and do it in a confidential and appropriate way.
This same questioner asks, why would someone risk a test when there's a chance it could mean two or three weeks of mandatory quarantine plus that contact tracing?
I would hope that people would do it in part to protect a loved one and to reduce the chance that they will infect someone else who may be an older person at home, maybe a grandparent. But I would hope it would be part of the community spirit, that we're all in this together and we're all trying to fight this pandemic.
It appears that in many places that are not coronavirus hot spots, a lot of people don't personally know of anyone who has been infected. As a public health expert, do you think this phenomenon could produce a false sense of security?
Oh I think it almost certainly does produce a false sense of security. Fundamentally, we know that the virus may not reach sparsely populated areas as quickly as it does more densely populated areas. But there's no reason to think that communities in rural areas or small towns that haven't been infected yet won't eventually be affected. And so if this seems like a distant threat to people living in a rural community, all I can say is, in all likelihood it will get there eventually.