Friday, 10 April 2020

Corona Virus Update: exit strategy, masks, aerosols, loss of smell and taste (part 28)

Prof. Dr. Christian Drosten
Today's podcast had a wide range of topics, from the proposal for an exit from the lockdown by the German National Science Academy, to face masks (which is one of their proposals), to transfer of the SARS-CoV-2 virus by droplets and by tiny airborne particles (aerosols), how long a patient is contagious and a new study on the loss of smell and taste as a symptom of COVID-19.

The Corona Virus Update Podcast is an initiative of the German public radio channel NDR Info. Today science journalist Anja Martini does the interview with Prof. Dr. Christian Drosten. He is an expert for emerging viruses at the [[research hospital Charité]]. Fittingly the hospital was founded outside the city walls of Berlin three centuries ago to help fight an outbreak of the bubonic plague, which had already depopulated large parts of East Prussia.

An exit strategy

In the previous podcast Drosten talked about a study, which suggested that a mobile phone app, which can help trace back contacts of infected people, would be quite effective in reducing the spread of the virus. About as powerful as a lockdown.

Three day later the German National Academy of Science, Leopoldina, recommended three measures, which could become an alternative for a lockdown. 1) This app, 2) more testing, 3) wearing simple masks in public.

[EDIT: It goes viral in America that Apple and Google will somehow help with such apps. That most of the work is already done by governments is not something that gets much millimetres, while it is not that clear to me what Apple and Google will contribute. They say first an API. Maybe that helps to make different apps interoperable? In a second phase they want to integrate it in the OS. If that means that the data (also) goes to Apple and Google, that would be an efficient way to kill the project.]

Leopoldina presents a model, which suggests this would be enough to keep new infections per day close to zero in May, although they also show data from South Korea, which has a similar strategy, were there is still a decent amount of new infections going on. So the model does not capture reality fully.

Anja Martini:
The Leopoldina, the National Academy of Science, issued a second statement from its working group on the virus at the end of last week. You are also part of this working group. ... It recommends - over and above the measures that we have already taken so far, in other words keeping our distance - hygiene and quarantine in the event of suspicion, isolation: Consistent wearing of masks, including in local public transport and at school, more tests, including random tests, and the use of cell phone data, which we have already discussed here. If this is done, the number of people infected by an infected person could, according to the calculations, be reduced to less than one by the middle or end of May. Even if, after Eastern, more public life were to be gradually allowed again. That is cause for optimism for the time being, isn't it? Please explain this prognosis to us!
Christian Drosten:
Of course, one looks for ways to get out of the current measures. And an organisation like the Leopoldina, which is made up of scientists, also looks at the latest scientific data. Just last week we discussed a study published in "Science" about the effects that can be expected from such mobile apps, i.e. mobile phone apps that allow much more detailed and faster case tracking.

We can simply track a certain number of infected people at the local health departments. At some point, the capacity runs out. You can't make an infinite number of phone calls and contact an infinite number of contacts and tell them to stay home and so on. It just runs out at some point. A mobile app is not exhausted that quickly and it also gets behind it much faster. That's the one provision there.
If the modelling study on the impact of this app is right, this should do most of the work.

So one can wonder why masks are additionally proposed by Leopoldina. My impression from previous podcasts is that Drosten is quite sceptical of masks. While there is evidence that they reduce the amount of viral material an infected person produces, there is not much evidence on how much they would contain the spread of the virus.

Maybe that lack of strong evidence is why Drosten wonders whether people would be persuaded to wear the masks. I do not see much of a problem, but maybe I am too optimistic. Wearing a mask is a much smaller limitation than staying at home. And I recently came by this beautiful photo of California during the Spanish flu, where people are wearing masks at an outdoor barber shop. Another culture not used to masks that were willing to wear them when needed.
You can achieve considerable increases if you add some general effects [additional measures] to this very special tracking via mobile apps. A general effect can be the wearing of masks if everyone does it. In our society, we certainly do not have the best starting conditions to let everyone wear masks. There will quickly be people who say they don't want to, they don't see the point or they can't do it.
We have currently, of course, an additional argument in public, namely: you cannot buy any masks at all, because there are none. That is why it is of course not very promising at first to consider what would happen if a general obligation to wear masks were to be imposed ad hoc?

This is a relatively complicated phenomenon, ... to impose such a thing in a society where the whole thing is not culturally anchored and not trained. That is the one difficulty. It is of course taken into consideration in a forum like the Leopoldina, where social scientists, psychologists and so on are also represented. This is precisely why the totality of the expertise is represented, not only life scientists are in it, but also sociologist.

Types of masks

Christian Drosten:
We have hardly any scientific evidence that says that self-protection through simple masks works. Of course, there are much more complicated, elaborate masks for special wearers, i.e. for certain occupational groups, who also provide self-protection.

But these masks have actually never been available in large numbers. They are not so easy to produce so fast, as far as I know. By the way, they are also not easy to wear for everyone. You have to imagine that here in medicine there are preliminary occupational medical examinations for employees who have to wear these very safe self-protection masks in their professional life. Not everyone is able to do this, for example, if there is any doubt, the medical profession must carry out lung function tests. And something like that cannot be recommended for the normal population.
I am not sure I understand his claim on the simple masks:
With these [simple] masks it is the case, there is no scientific evidence of a benefit for self-protection. There is, however, starting evidence, which has not been very virus-specific so far, for the protection of others. But this of course presupposes that really everyone, everyone, everyone in society, in public life, must wear these masks.
I would expect that when half of all people do it you get half of the effect. But maybe Drosten means that for this to help for your own protection everyone would have to do it. Also if only half would do it, to help the others, one could expect that the participation drops. That is a kind of [[public goods game]] It could also be that he does not expect much of an effect and that half would thus really not be worth it.

Droplets and aerosols

A large part of the podcast was about the difference between droplets with virus and aerosols. Droplets would be defined as being large enough to drop to the ground by gravity within a minute, while aerosols can stay in the air for hours. It was a long and nuanced discussion about evidence on how these particles are produced and removed, how infectious they are and how important they are.

People are worried about the aerosols, about "airborne virus" because it means that you could be infected without having noticed someone coughing. But in the end the droplets are most important: "we are pretty sure that the vast majority of the viruses that are released in these diseases of the upper respiratory tract ... are these larger droplets - and they fall to the ground". So to focus on what is important, I only translated a small part:

Christian Drosten:
These large droplets over five microns (and they can can be much bigger, they can also be 100 micrometers, i.e. a tenth of a millimeter, so that you can really see them with the naked eye) - these are the droplets that we are talking about in a droplet infection. In other words, what you give off - which is part of a moist speech [when people spatter when they talk], for example, but also comes out when you cough or sneeze - and which falls to the ground within a radius of one and a half to two meters.

In this research into the common cold, we are pretty sure that the vast majority of the viruses that are released in these diseases of the upper respiratory tract (i.e. the diseases that mainly occur in the throat and nose) are these larger droplets - and they fall to the ground. Much of our precautions and infection prevention considerations are based on this insight.

Then there is something else, namely aerosols, whose particle size is less than five micrometers. For the experts, it must be said that this is of course not a sharply defined size, and an aerosol that really floats in the air and stays in the air longer, the actual droplets are even much smaller, they are less than one micrometer in size. ...

If I release such a droplet and it floats in the air in front of me, then it starts to dry and then it becomes smaller. The smaller it gets, the more likely it is that it will remain in the air for a long time. But at the same time there is another effect, namely when this droplet gets smaller and smaller, it will eventually be too small for the virus, and the virus will dry out and will no longer be infectious.

So on the one hand aerosols are potentially more problematic by staying in the air longer, on the other hand they are likely less contagious, while many studies only analyse whether virus is present, not whether the material is infectious. Reading such studies one should pay attention to this difference.

How long is someone contagious

An interesting preprint studied how much virus could be found in hospital rooms of COVID-19 patients.

Christian Drosten:
Wipe samples were taken - in 30 different hospital rooms, from 30 different patients, all of whom had the disease, in a hospital in Singapore, from all kinds of surfaces, and tested them for virus again.

By the way, I have to add here, in all these studies, especially the last study that we discussed first, and this one too, it is always only a viral detection of RNA and not of infectivity in the cell culture.
Anja Martini:
In other words, a virus that can be detected, but which possibly no longer infects anyone.
Christian Drosten:
Right, exactly. A desiccated virus, it still has the same amount of RNA and you can still detect it. None of this means anything directly about infectivity right now, it just means that virus has got there.

And here it is the case that a lot of deposited RNA has already been found in these samples. In the floor samples, for example, more than half of the wipe samples were virus-positive, i.e. viral RNA could be detected - which suggests that the virus is deposited to a considerable extent, which is a sign of the fact that the virus is in fact deposits considerably, which favours the concept of a coarser drops.

But then, something else and very important, I think: With these 30 patients were these virus swab samples always positive only in the first week of symptoms. In the the second week, when the patients were still definitely sick the wipe samples were no longer positive. So no more virus settles on the surfaces, was accordingly also no significant virus concentration more in the room air.
Note, this is just one study. Decisions should be based on all available evidence and an uncertainty estimate.

Infection via surfaces

If I understand it right, when someone coughs in their hands and then shakes hands, that is seen as droplet transmission and not as transmission via a surface. This route is important and a reason for the advice not to cough in your hands and to wash them regularly.

Anja Martini:
The insight we have from this is that we are infected via the air we breathe, via coughing, via aerosols, and not, as is a question much asked by listeners here, what is actually the case with infection via surfaces?
Christian Drosten:
Infection via surfaces themselves has been modelled, for example, in the study by Christophe Fraser that we discussed last week. He comes to the conclusion that perhaps ten percent of all transmissions could function via surfaces at all.

Many people I talk to don't really believe in the relevance of surface transmission. ...

We do not currently assume that this virus is significantly transmitted via surfaces. The current measures to prevent transmission are aimed at preventing both droplet and airborne transmission, especially - to say it again - droplet transmission. And the studies that have now been discussed here, that have now been published, do not suggest - even if small-droplet aerosols have been detected - that this mechanism would be the main focus.
Anja Martini:
This means, once again asking from the consumer's point of view, ... can we actually neglect surface disinfectants in our private lives?
Christian Drosten:
I am almost sure that it is not worthwhile to pay a lot of attention in the household to treat all kinds of surfaces with disinfectant. In a hospital, of course, this may be different. ...
My impression is that this was scientific "may", which mostly means "will". We sometimes talk in a somewhat weird way.
Images from television, for example, in China, where tanker lorries are driving through the streets with disinfectants, I think that has more of a psychological effect on the population than a real effect in curbing the transmission of infection.
I love those videos of teams with disinfectant sprayers walking through the streets as if they could be eye to eye with a terrorist any second.

Loss of smell and taste

Anja Martini:
What does a possible disease or even an infection with the virus actually do to the sense of taste and smell? This was already something of an observation in the press. There was also a Belgian study. Now there is one from Iran based on an online questionnaire.
Christian Drosten:
Yes, I think it's a very interesting study. There are already clear indications. In the Munich patient observation we have already seen a loss of the sense of taste and smell in almost half of the cases. So this has already been published.

There is now even a functional study that has just been published - and it says that it is a very specific type of cells in the olfactory system, in the nose, in the olfactory bulb, that is actually infected and affected by this virus.

But that is not what we want to discuss here. Interestingly, it is a study from Iran. I think it is simply great to see that this kind of useful research also comes from a country that is highly affected and where we all know that the data situation is unclear. The science there has to work in a difficult system, has also difficulties, for example, to get certain reagents. But but here comes a very interesting study, from the preprint realm, to the public.

Iranian scientists conducted a survey - also supported by apps and the Internet - and reached 15,000 people with this survey. Of these, 10,000 actually had a loss or impairment of the sense of smell. In fact, 76 percent of these 10,000 patients - an impressively large number - had a sudden loss.

You can tell the difference between saying that suddenly I couldn't smell anything anymore. Or whether you say, well, I just had a cold. And 75 percent, a similarly high rate, actually had influenza-like symptoms. So now that not only a runny nose is part of it, but also a noticeable fever and so on. This was clarified by questionnaires.

83 percent also had a loss of taste, which was also described, also in the Munich patients, so that a loss of taste is also involved. They could no longer taste or smell anything. ...

And if I suddenly couldn't smell anything anymore in my everyday life, I would stay at home and try to clarify what is going on with me at the moment, in the current situation.

Other podcasts

Part 27: Corona Virus Update: tracking infections by App and do go outside

Part 23: Corona Virus Update: need for speed in funding and publication, virus arrival, from pandemic to endemic

Part 22: Corona Virus Update: scientific studies on cures for COVID-19.

Part 21: Corona Virus Update: tests, tests, tests and how they work.

Part 20: Corona Virus Update: Case-tracking teams, slowdown in Germany, infectiousness.

Part 19: Corona Virus Update with Christian Drosten: going outside, face masks, children and media troubles.

Part 18: Leading German virologist Prof. Dr. Christian Drosten goes viral, topics: Air pollution, data quality, sequencing, immunity, seasonality & curfews.

Related reading

This Corona Virus Update podcast and its German transcript. Part 28.

All podcasts and German transcripts of the Corona Virus Update.

Respiratory virus shedding in exhaled breath and efficacy of face masks

Detection of Air and Surface Contamination by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Hospital Rooms of Infected Patients

Coincidence of COVID-19 epidemic and olfactory dysfunction outbreak

Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1

A paper from 2004 that shows that even while normally breathing out some people produce tiny droplets: Inhaling to mitigate exhaled bioaerosols

A letter from the American Academy of Sciences on droplets and aerosols.

News article in Science Magazine on the relevance of small droplets: You may be able to spread coronavirus just by breathing, new report finds

1 comment:

  1. TCW, do you have a reputable scientific source for your claim? If not I prefer not to publish your comment.


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