Anosmia now on the Covid-19 symptom list

The UK government recently added anosmia - the loss of the sense of smell - to the list of symptoms that people infected with coronavirus might develop, qualifying them for testing. And it turns out that losing your sense of smell is a much more powerful predictor of coronavirus infection than having a fever, previously the leading criterion: Over 60% of people develop anosmia, and in sixteen percent of people, it's the only symptom they show. This has emerged thanks to a free phone application called the "Covid Symptom Study App" launched by Kings College London researcher Tim Spector, and it seems his figures from over 3 million users have finally provoked the government into action…

Tim - We're currently picking up 17 symptoms and we're adding to them on a nearly weekly basis as people report them back to us. When this virus was first reported, they were just cough and fever, and until recently that was still the NHS Public Health England advice. We noticed pretty soon after launching on the 24th of March that many people were reporting a lack of smell and taste and they were telling us there was nowhere on the app. So we quickly added it to the app and within about a week we had enough cases that we knew this wasn't just made up. And over the next few weeks did some analysis to show that in a subset that were having swab testing, this was about the best predictor you could have of a positive viral swab test. It was actually better than fever or cough. And so we put a paper online about it. We told the government about it six weeks ago, and these extra symptoms that aren't just like flu should be taken more seriously.

Chris - How many people have you got signed up to the app now?

Tim - We have 3.25 million have actually entered their details on the app and about 1.5 million who are logging every single day.

Chris - How does it work then? They download the app and then what information does it solicit from them and how frequently?

Tim - They download the app and you basically you have to fill in a few personal details. You give your postcode, you're asked a few health details and then you're asked whether today you're feeling well or not. If you say you're feeling well, that's it. You finish. If you say you're not feeling well, you get a drop down menu of 17 potential symptoms at the moment and you log those. As people, if they've been logging they're healthy for a while and they get ill, many of them are being sent a swab test and from that we're working out what the best combination of symptoms are that match a positive test.

Chris - Why did it take the government so long, do you think, from the time that they were made aware that there was this association before it's finally formally admitted to the case definition of "if you've got this symptom, you might have coronavirus"?

Tim - It's a very good question. I can only speculate. The key thing as I've mentioned is that at least 17 other countries have several weeks before include it in their list, and France did this about six, seven weeks ago. The excuse the deputy chief medical officer gave to the press was that it had a very small effect. Therefore they didn't think it was worth confusing the public with. Our data disagree with that by a factor of 10. They said it only affected 2%, our data show, it's closer to 16, 17%.

Chris - So what fraction of people have loss of sense of smell and taste then, as a proportion of all cases of coronavirus infection?

Tim - Of the people who tested positive, it's around 60%.

Chris - And what % of people have exclusively just loss of smell and taste and nothing else?

Tim - It's about 16% have it and do not have fever or cough. Now they wouldn't be missed. But for the last few months they would have been missed.

Chris - Taking your figures into account then, how many cases potentially have we overlooked of coronavirus hitherto?

Tim - If we'd done this right at the beginning, at the end of March, and we estimate around 4 million people contracted it, we're talking at least half a million people.

Chris - It's quite a lot, isn't it?

Tim - It is. And I think it's a bit sad we didn't react faster. But the important thing is now that we start to say, "well, how can we use this information positively"? At the moment we seem very obsessed with giving people temperature checks at airports and hospitals and care homes. And our data suggests that we'd actually pick up more cases if we gave them some smell tests.

Chris - So do you think at the airport then, what we should have is a bunch of roses and people have to tell us what they're smelling?

Tim - Yes. And you may be laughing, but they're already doing this in some Asian countries. And I think we've just got to realise this is one of the strangest diseases doctors have ever seen. And we have to be very open minded about collecting all the information and using everything, even if it sounds a bit wacky, to try and reduce its impact.

Chris - So there's a reason if you needed one to meet your loved one at the airport with a bunch of flowers, at least if both of you can smell them, you know, neither of you are incubating coronavirus. But why should the infection cause people to lose their sense of smell in the first place? Well Carl Philpott is a consultant ear, nose and throat specialist, he's at the university of East Anglia.

Carl - There are a few theories working at the moment as to why this is happening. We know that the virus is very concentrated in the nose. One of the theories is that it's infecting the cells at the top of the nose, that are what we call the supporting layer, around the smell receptors. And by doing so, it's effectively squeezing the receptor cells themselves, they're not working properly.

Chris - And will it come back? Because obviously people are very worried, they're rendered abruptly, so-called "anosmic". They say, "well, I suddenly can't start smelling things". Is this going to recover?

Carl - What we're seeing in the data so far is that 50% are getting it back completely within seven to 14 days, another 40% are getting it back partially. And then about 10% so far are not recovering their sense of smell. And I guess at this stage it's too early to say how long they'll be without it. Whether that will be a more lasting effect.

Chris - That's quite a lot though, isn't it, of people who are potentially going to be rendered longterm, lacking in smell and possibly taste.

Carl - Absolutely. I mean, we've been talking about this in research circles that it could be in the tens of thousands of people that have a more lasting effect on their sense of smell or taste.

Chris - And what might be the consequences of that?

Carl - Well, the day to day impact of being without your sense of smell. Let's start with food and nutrition, you know, weight in relation to that. General well being, personal hygiene, and interaction with partners. Sexual attraction is all linked into smell. Memories. There's a whole sort of swathe of things that can be impacted by that.