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Explained: Can Covid-19 hit sense of smell?

US disease control authority has newly listed loss of sense of smell among COVID-19 symptoms. A look at this less commonly described symptom, and what the evidence worldwide has shown so far.

Written by Abantika Ghosh | New Delhi | Updated: May 2, 2020 10:21:23 am
Explained: Can Covid-19 hit sense of smell? Nasal swab being collected in New Delhi last week. (PTI Photo)

Earlier this week, the US Centers for Disease Control and Prevention (CDC) introduced a new loss of taste or smell” in a list of COVID-19 symptoms. While loss of smell is a known symptom of several diseases, it is less common than hearing loss or vision loss, and patients become conscious of it later than they would notice a fever or body ache.

What has the CDC said?

“People with COVID-19 have had a wide range of symptoms reported — ranging from mild symptoms to severe illness. Symptoms may appear 2-14 days after exposure to the virus. People with these symptoms or combinations of symptoms may have COVID-19 — Cough and Shortness of breath or difficulty breathing,” the CDC says.

In addition, it lists symptoms that include fever, chills, repeated shaking with chills, muscle pain, headache, sore throat, and a new loss of taste or smell. If a patients has two or more of these symptoms, the CDC says there is a chance that the person has COVID-2019 infection.

Why is the inclusion of loss of smell important?

Rhinology, ENT and otolaryngology experts have been pushing for inclusion of loss of smell — known as anosmia — in the list of symptoms for some time now. These include the American Academy of Otolaryngology-Head and Neck Surgery and the British Association of Otorhinolaryngology.

Chills are associated with many other infections, such as malaria, and muscle pain and body ache are typically associated with common flu. For these reasons, health experts have repeatedly noted that it is impossible to symptomatically differentiate between COVID-19 and the common flu.

Anosmia, however, is a less common symptom. Johns Hopkins University too lists unexplained loss of taste or smell, alongside cough, fever, shortness of breath, muscle aches, sore throat, diarrohoea, headache and also fatigue among the symptoms.

Most of the other symptoms are common among the lists developed by various international health organisations. According to the World Health Organization: “The most common symptoms of COVID-19 are fever, dry cough, and tiredness. Some patients may have aches and pains, nasal congestion, sore throat or diarrhea. These symptoms are usually mild and begin gradually.”

The WHO list of symptoms has been adopted by the Health Ministry in India.

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Why do people lose their sense of smell?

It can happen during a severe cold, when we say the nose is “blocked”. Only, this is hyposmia, a reduced sense of smell rather than a complete loss of it. According to Mayo Clinic: “A stuffy nose from a cold is a common cause for a partial, temporary loss of smell. A blockage in the nasal passages caused by a polyp or a nasal fracture also is a common cause. Normal aging can cause a loss of smell too, particularly after age 60.”

It is usually also associated with reduced appetite because our sense of smell is part of our sense of taste. That is why during a cold, we seem to lack taste in our food. In a 2017 review in the Journal Chemical Senses, researchers from Wageningen University in Netherlands wrote: “Anosmia and hyposmia, the inability or decreased ability to smell, is estimated to afflict 3-20% of the population. Risk of olfactory dysfunction increases with old age and may also result from chronic sinonasal diseases, severe head trauma, and upper respiratory infections, or neurodegenerative diseases.”

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Other diseases with anosmia among its symptoms include Parkinson’s disease, Alzheimer’s disease and multiple sclerosis. In such cases, it is permanent.

Is this the first time COVID-19 has been linked to a loss of sense of smell new?

No. There have been very early reports from various countries about some patients complaining of a loss of smell. According to ENT UK, a professional membership body, “There is already good evidence from South Korea, China and Italy that significant numbers of patients with proven COVID-19 infection have developed anosmia/hyposmia. In Germany it is reported that more than 2 in 3 confirmed cases have anosmia. In South Korea, where testing has been more widespread, 30% of patients testing positive have had anosmia as their major presenting symptom in otherwise mild cases.”

In a communication with Public Health England on COVID-related anosmia, ENT UK also flagged the fact that many people report only anosmia without any of the more usual symptoms like fever etc. “Iran has reported a sudden increase in cases of isolated anosmia, and many colleagues from the US, France and Northern Italy have the same experience. I have personally seen four patients this week, all under 40, and otherwise asymptomatic except for the recent onset of anosmia – I usually see roughly no more than one a month. I think these patients may be some of the hitherto hidden carriers that have facilitated the rapid spread of COVID-19. Unfortunately, these patients do not meet current criteria for testing or self- isolation,” wrote Prof Claire Hopkins, president of the British Rhinological Society, and Prof Nirmal Kumar, president of ENT UK.

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In an article in The Lancet Infectious Diseases, researchers from the US Medical Corps wrote: “Our multinational group, including one otolaryngologist currently infected with COVID-19 and experiencing anosmia and dysgeusia (altered sense of taste), suggest that physicians evaluating patients with acute-onset loss of smell or taste, particularly in the context of a patent nasal airway (ie, non-conductive loss), should have a high index of suspicion for concomitant SARS-CoV-2 infection.”

Have patients in India reported loss of sense of smell?

Some have. In a now viral clip, a doctor in Lutyen’s Delhi, who was quarantined after testing positive, talks about how he decided to get himself and his wife tested after he noticed, following a few days of cough and body ache, that he could not “smell perfume or agarbattis”.

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