Government advisers have been considering since March whether to include loss of smell among the criteria for deciding whether someone has Covid-19. Evidence that it is one of the symptoms is already strong and some scientists argue this is now an urgent step, as the lockdown is eased.
At first Dan, 23, dismissed his stuffy nose as hay fever, but when he couldn't taste his beans on toast, he began to worry he had come down with Covid-19.
"I thought something must be up so just to check I poured myself a strong glass of orange squash," says Dan, who works as a respiratory physiotherapist at a West Midlands hospital.
"I just couldn't taste that at all." He tried inhaling a nasal decongestant made with eucalyptus oil and menthol, but couldn't smell that either.
Dan worried that if he did have Covid-19, going into work might have serious consequences. But when he called the NHS helpline, 111, he was told there was no problem as he didn't have a cough or a high temperature.
"They were obviously reading off a script and they said, 'You're good to go back to work,' which I felt a bit funny about," Dan says. "To have suddenly lost my sense of smell and taste when I work with some patients who have coronavirus felt like too much of a coincidence."
Ignoring this advice, he began self-isolating, as did the rest of his family, including his mum, a podiatrist whose clients include vulnerable elderly people, and his sister, an intensive care nurse at a children's hospital.
Meanwhile Dan's manager arranged a coronavirus test for him - and a few days later it came back positive.
"Based on government advice alone, I would have been back at work, going from patient to patient and potentially giving them coronavirus," says Dan.
That was in April, just after the Easter bank holiday, but the advice from 111 and on the NHS website remains the same today. The website mentions only two symptoms, a high temperature and a new continuous cough.
This is frustrating for Ear Nose and Throat consultant Prof Claire Hopkins, president of the British Rhinological Society, who has been arguing for eight weeks that people suddenly losing their sense of smell should be told to self-isolate.
She accepts that when she first gave this advice to Public Health England on 19 March - later published as a joint press release with Prof Nirmal Kumar, president of the ENT surgeons' professional body, ENT UK - the evidence for loss of smell being a symptom of Covid-19 was anecdotal, but she now argues that it is "robust".
At first there were signs that Hopkins might be succeeding in getting her point across.
Loss of taste or loss of smell?
- With Covid-19 loss of smell and taste can occur suddenly, Claire Hopkins says, and without an accompanying blocked nose
- This may be the first symptom to appear, or may start at the same time as other symptoms - and in some cases it is the only symptom
- Perception of flavour is dependent on the sense of smell so patients who cannot smell may stop enjoying food
- Loss of smell is more common in people under 40, Claire Hopkins says, and could be a marker of more mild disease
On 30 March, the government's chief scientific adviser, Sir Patrick Vallance, said at the government's daily briefing that loss of taste and smell "does seem to be a feature of this, from what people are reporting, and it is obviously something that people should take into account as they think about their symptoms".
At the briefing on 3 April, deputy chief medical officer Prof Jonathan Van-Tam said that experts did not at that stage think loss of smell and taste needed to be part of the "case definition" - the set of criteria used to determine whether someone has the disease - but that the government's advisory group on new and emerging respiratory virus threats (Nervtag) had been asked to look into the question.
Throughout this period, Claire Hopkins has been among those updating Nervtag on data that she and medical colleagues from a range of countries have been collecting.
First results from the King's College coronavirus tracker app, published on 1 April, found that 59% of users testing positive for Covid-19 reported loss of smell or taste. The latest research from the same team, produced in collaboration with partners in Massachusetts and Nottingham and published in Nature Medicine, found that 65% of the more than 7,000 users of the app who had tested positive for Covid-19 reported loss of smell and taste, compared with just over a fifth of those who tested negative. This, the authors say, suggests that loss of smell - anosmia - is a stronger predictor of Covid-19 than fever.
Where to get help
- Most people who lose the sense of smell as a result of Covid-19 regain it in seven to 14 days, Claire Hopkins says, but it's taking longer in about 10% of cases
- Post-viral anosmia (loss of smell) can be permanent, she says, but recovery remains possible for at least 18 months
- The charities AbScent and Fifth Sense can provide support, and give advice on smell training
- See also: NHS advice - lost or changed sense of smell
Hopkins herself has been working with teams of doctors in Italy, France, Belgium, and Spain measuring the ability to smell of thousands of patients with known Covid-19 infection, and has concluded that sudden loss of smell, when not accompanied by other symptoms such as a blocked nose or a head injury, is in fact the best predictor of infection.
"We've been able to show that in groups of patients that have lost their sense of smell without any other symptoms, there's a greater than 95% chance it is due to Covid-19 at the moment," she says.
By contrast, fever is not a good marker, Hopkins argues, because many things can cause a fever, and this symptom is only present in about 40% of patients with Covid-19. By focusing only on fever and a continuous cough, she argues, citing published papers, the NHS will only catch 50% to 60% of cases.
Hopkins has also been involved with the Global Consortium for Chemosensory Research, which has published results from a survey of more than 4,000 patients diagnosed with Covid-19, who reported on average an 80% drop in ability to smell and a 69% drop in ability to taste.
All these results suggest to Hopkins that key workers who have continued working during the lockdown despite losing the sense of smell have probably been contributing to the spread of the virus.
"There are a significant number of essential workers, who got in contact and told me that, because they don't meet the criteria, their employers have told them that they still have to go to work," she says. "For example somebody who's involved in food delivery, potentially delivering food to vulnerable groups, is still having to go out despite having very recently lost his sense of smell, and almost certainly having Covid-19."
As the lockdown eases, this group of people will grow, Hopkins says, unless the 111 helpline changes its criteria.
"I can still put in my symptoms into NHS 111 and claim to have muscle ache, fatigue, loss of smell, diarrhoea [all recognised as symptoms of Covid-19 by the WHO] and be told that I don't have coronavirus," says Hopkins. "I think that is now actually, clinically, negligence."
Prof Peter Horby, director of the epidemic diseases research group at the University of Oxford, who chairs Nervtag, told the BBC it was important to find the cluster of symptoms that most reliably identifies Covid-19 cases at an early stage of the illness, but also distinguishes it from other respiratory infections, so as to avoid large numbers of false-positive cases in the winter.
"Anosmia is certainly in the mix for a revision of the case definition," he said. He later added that he expected it to be included as a symptom in future iterations of the app being piloted on the Isle of Wight.
Nervtag member Dr Ben Killingley, a consultant at University College London Hospital, commented that loss of smell was a "definitely a symptom" of Covid-19 but the question was "whether the positive predictive value of the symptom is high enough to warrant its inclusion in a case definition".
He added: "Whether the symptom is included in the symptom/contact tracing app will give you a clue, though this remains in development."
Another member of the advisory group, Prof Andrew Hayward, director of the UCL Institute of Epidemiology and Health Care, commented: "All I can really say is that Nervtag have recently provided scientific advice on this and it is being considered by the Department of Health and Social Care and other bodies, so I would expect an announcement about case definitions soon."
A DHSC press officer told the BBC: "Symptoms of Covid-19, including loss of smell and taste, have remained under constant review by an expert scientific group. At all times during this global pandemic we have been guided by the evidence, taking the right steps at the right time to deliver a strategy designed to protect the NHS and save lives."
As for Dan, he regularly tested his taste buds by eating salt and vinegar crisps, and noticed a gradual improvement.
"After five days I could tell they were salt and vinegar but it wasn't normal at all," he says.
His sense of smell is taking longer to return.
"When I'm cooking and putting garlic in a pan and everyone says, 'Ooh, that garlic smells nice,' it takes me a little bit longer to get that smell," he says.
He's very glad his boss acted decisively to get him tested.
"It was credit to them, to be fair, because they spotted the signs early," he says. "And I know that other places might not have arranged testing, and I would still have been treating patients."
Update 19 May 2020: The original version of this story quoted Prof Peter Horby saying that anosmia was a symptom included in the contact tracing app being tested on the Isle of Wight. He later clarified that he expected it to be included in future iterations of the app.
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