Some people who have had COVID-19 have reported losing their sense of smell, leading to reports that it may be a unique symptom of the virus, particularly among those who are only mildly affected.

So far, no peer-reviewed research has been published that has asked large numbers of patients with confirmed COVID-19 about their sense of smell, though case reports exist, a low level of evidence.

For now, we do not know how many people with COVID-19 experience a loss of smell or taste, what proportion of people with loss of smell or taste have coronavirus infection or how any data might compare to the rates for other viruses.

Most of the evidence is on single cases, which means it comes from patients sharing information about their symptoms with others. This doesn’t mean that the claim is necessarily untrue, we just need stronger evidence before we can say for sure.

What is clear is that not everyone with COVID-19 reports this symptom, and there are other reasons why you might lose your sense of smell. Cough and fever continue to be the most important symptoms of COVID-19 to look out for.

 

Where did the story come from?

There has been widespread media coverage of claims that loss of smell or taste is signs of coronavirus infection. Many of these reported a statement from ENT UK, a professional body representing doctors working in ear, nose and throat specialities in the UK. The statement discussed the evidence and suggested that patients with loss of smell could also be asked to self-isolate.

 

What is the basis for the claim?

The statement from ENT UK said that, in South Korea, “30% of patients testing positive [for the novel coronavirus] have had anosmia [loss of sense of smell] as their major presenting symptom in otherwise mild cases.” It also said that “there have been a rapidly growing number of reports of a significant increase in the number of patients presenting with anosmia in the absence of other symptoms.”

To investigate the issue, the Oxford Centre for Evidence-Based Medicine carried out a systematic search and rapid review of the published evidence around the total or partial loss of smell in people with coronavirus. They also consulted with experts.

The Centre found no studies from peer-reviewed journals reporting on the loss of sense of smell in COVID-19. Over 50 peer-reviewed studies were identified which reported on symptoms of COVID-19, and none mentioned a loss of smell.

The found one small study from China which reported that about 5% of hospitalised COVID-19 patients had a partial loss of smell. However, this study had not yet been verified by peer review, so should be taken cautiously.

They found that the claim from South Korea was based on a news report quoting a doctor, not on published data. Other reports of patients presenting with a loss of smell came from a private internet message board used by ENT doctors.

BBC News recently reported that early results from an app that tracks symptoms across the UK. It found 59% of 579 people who reported having coronavirus infection confirmed by a test said they had experienced a loss of smell or taste. However, we don’t know how representative of those with coronavirus this sample is.

 

What do trusted sources say?

The World Health Organization says: “The most common symptoms of COVID-19 are fever, tiredness, and dry cough. Some patients may have aches and pains, nasal congestion, runny nose, sore throat or diarrhoea.” Loss of smell is not mentioned.

The Oxford CEBM review concluded: “The current evidence base to suggest changes in olfactory sensation [smell] is a feature of COVID-19 is limited and inconclusive. More evidence is required to establish whether there is a link between changes in olfaction and COVID-19.”  The centre goes on to encourage clinicians assessing suspected cases to incorporate questions around the loss of smell.

Analysis by EIU Healthcare, supported by Reckitt Benckiser

 

Citation

  1. Loss of sense of smell as marker of COVID-19 infection. ENT UK. 21 March 2020. Available at https://www.entuk.org/sites/default/files/files/Loss%20of%20sense%20of%20smell%20as%20marker%20of%20COVID.pdf (Accessed 2 April 2020)

 

Reading list

1.     O’Donavan J et al. What is the evidence for anosmia (loss of smell) as a clinical feature of COVID-19? Oxford Centre for Evidence Based Medicine. 23 March 2020. Available at https://www.cebm.net/covid-19/what-is-the-evidence-for-anosmia-loss-of-smell-as-a-clinical-feature-of-covid-19/ (Accessed 2 April 2020)

2.     World Health Organization. Q&A on coronaviruses (COVID-19). 9 March 2020. (Accessed 2 April 2020)