Does Loss of Smell Require COVID-19 Precautions?

The loss of smell or taste could occur with coronavirus disease 2019 (COVID-19) in absence of other symptoms, according to case reports in the US and abroad. This could heighten the risk of exposure for unknowing contacts and add to presenting conditions that could warrant testing for the novel coronavirus.

A report from Norway described that the daughter-in-law of an elderly patient with COVID-19 experienced loss of smell approximately 1 week after she had been in close contact with him, before his hospitalization. Her husband also developed loss of taste shortly after. Both individuals subsequently tested positive for SARS-CoV-2 RNA without developing other symptoms, and both experienced return of these senses after approximately 10 and 16 days, respectively.

"National and international health authorities should consider whether isolated disturbances of smell and/or taste are a sufficient basis for testing for COVID-19 and/or isolation to limit spread of the infection," the report concluded.

In a report from France, a patient with loss of smell who subsequently tested positive for the virus was found on CT scan with confirming MRI to have bilateral inflammatory obstruction of the olfactory clefts, with no anomalies of the olfactory bulbs and tracts.

This obstructive inflammation of olfactory clefts, the report indicated, "severely impaired the olfactory function by preventing odorant molecules from reaching the olfactory epithelium."

Others are investigating the possible underlying mechanisms. One group has determined that, in both mouse and human datasets, olfactory neurons do not express 2 key genes associated with the virus entry, ACE2 and TMPRSS2, but that these are both expressed in olfactory epithelial support cells, stem cells, and cells in the nasal respiratory epithelium.

Recognizing that loss of sense of smell could be a marker of COVID-19 infection, the British Rhinological Society issued a guidance which, in addition to encouraging quarantine of the affected patient and personal protective equipment for consulting health care workers, cautioned against using steroids for the presentation.

"Given the potential for COVID-19 to present with anosmia, and the reports that corticosteroid use may increase the severity of infection, we would advise against use of oral steroids in the treatment of new onset anosmia during the pandemic, particularly if it is unrelated to head trauma or nasal pathology such as nasal polyps," the guidance stated.

Another agency in the UK, the Centre for Evidence-Based Medicine (CEBM), has issued its own report on anosmia and COVID-19, finding that the evidence linking the symptom to the viral disease to date is "limited and inconclusive". The CEBM report declares, "more evidence is required to establish whether there is a link between changes in olfaction and COVID-19".

The American Academy of Otolaryngology-Head and Neck Surgery has also recognized these reports as anecdotal and not yet conclusive, albeit accumulating, and has developed a COVID-19 Anosmia Reporting Tool, "in an effort to establish the importance of these symptoms in diagnosis and progression of COVID-19."

While more evidence is being gathered, otolaryngologists at Stanford University School of Medicine, Stanford, CA, have developed their own guidelines on how practitioners can protect themselves in caring for patients with COVID-19.

"Otolaryngologists are at unique risk due to the close contact with mucus membranes of the upper respiratory tract and have been among the most affected healthcare workers in Wuhan, China," they warn.