Olfactory Dysfunction in COVID-19

Abstract

As of May 1, 2020, more than 3 000 000 people worldwide have been infected with the novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The CDC has highlighted key symptoms that may suggest coronavirus disease 2019 (COVID-19), including cough, shortness of breath or difficulty breathing, fever, chills, muscle pain, sore throat, and new loss of smell or taste. 1 The inclusion of loss of smell or taste among these symptoms follows the emergence of evidence that suggests that COVID-19 frequently impairs the sense of smell. For example, in a study from Iran, 59 of 60 patients hospitalized with COVID-19 were found to have an impaired sense of smell according to psychophysical olfactory testing. 2 Olfactory dysfunction (OD), defined as the reduced or distorted ability to smell during sniffing (orthonasal olfaction) or eating (retronasal olfaction), is often reported in mild or even asymptomatic cases; in a study from Italy, 64% of 202 mildly symptomatic patients reported impaired olfaction. 3 The possibility that OD could act as a marker for disease, particularly among individuals who are otherwise minimally symptomatic or asymptomatic, prompted organizations, such as the American Academy of Otolaryngology-Head and Neck Surgery 4 and ENT UK, 5 to recommend inclusion of sudden-onset loss of smell and/or taste as part of the diagnostic criteria for COVID-19 disease, as has now been done by the CDC. These organizations suggest that new-onset OD is sufficient to justify self-isolation and the use of personal protective equipment (PPE) by medical staff evaluating patients with this clinical problem.

Psychophysical tests reveal impaired olfaction but preserved gustation in COVID‐19 patients

“…The subjectively altered taste is most likely caused by impaired retronasal olfaction. 4 To the best of our knowledge, this controlled prospective trial shows for the first time that COVID-19 is tightly associated with olfactory loss but not with gustatory dysfunction when tested psychophysically. Our results may be limited by the relatively small number of study participants.…”

“…2,3 These pathognomonic symptoms have led to the consensus that olfactory and gustatory defects should equally be regarded as highly suspicious for severe acute respiratory syndromecoronavirus-2 (SARS-CoV-2) infection, even in the absence of other symptoms. 4 Because of home quarantine and the short duration of chemosensitive disorders, reports so far have mostly been retrospective. Psychophysical tests of olfactory and gustatory function have mainly been performed in hospitalized patients only.…”

Short- and potential long-term adverse health outcomes of COVID-19: a rapid review

“…It is proposed that SARS-CoV-2 binds to ACE2 receptor, which triggers a series of signalling cascades and potentially leads to different adverse neurological outcomes, e.g. olfactory dysfunction after entering the brain by systemic circulation or through the nasal cavity [ 51 ].…”

Gustatory Dysfunction: A Highly Specific and Smell-Independent Symptom of COVID-19

“…Therefore, olfactory dysfunctions could represent a sign of neuroinvasion, while ageusia and hypogeusia would not have any possible interesting pathogenetic implication. Secondly, the gustatory disturbances have generally been classified as a consequence of the retronasal olfactory loss and for this reason they have been often overlooked [6].…”