Association of COVID-19 with Anosmia and Hypogeusia

Dear Editor

As of May 15, 2020, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causing coronavirus disease (COVID-19) that emerged in late 2019, in Wuhan, China, and declared a pandemic by the World Health Organization, now at over 4.3 million confirmed cases, with 295,101 confirmed deaths across 215 countries, areas or territories.¹ Many patients who are suffering from this viral illness report a sudden onset loss of smell and taste sensation.² Post-viral anosmia occurs following direct viral damage to the olfactory receptors and retrograde neuronal degeneration of the central conducting pathways.³ In a study by Lee et al, 80% of the patients recovered from anosmia after one year, while female patients had a better outcome.⁴

There is a growing concern among physicians because of an increase in reported cases of anosmia in COVID-19 patients, which suggests neurological involvement. Respiratory epithelium (RE) and Olfactory epithelium (OE) are the two components of nasal epithelium.⁵ Olfactory sensory neurons (OSN) in the OE recognize odor and convey signals to the brain via olfactory bulbs. Sustentacular cells, arising from the basal stem cells, maintain the structural integrity of the OE. SARS-CoV-2 enters cells by interacting with the ACE2 proteins on the target cells and uses proteases such as TMPRSS2. Bann et al. analyzed RNA-seq data sets to determine the expression of these genes in OE of mouse and human for CoV entry. Their investigation shows that these two key genes are not present in the OE of both mouse and human. However, olfactory supportive cells, stem cells, and perivascular cells express ACE2 and TMPRSS2—and suggest it as the mechanism of CoV cellular entry in OE.⁵

In some patients, anosmia and hypogeusia could be the presenting symptoms.⁶ However, we need robust data to validate this correlation in COVID-19. The reports largely come from regions with more vigorous testing, including the United States, China, South Korea, Italy, Germany, and Iran⁴. In the formerly described strain of the coronavirus, 10–15% of patients report anosmia, but the incidence is much higher in the novel SARS-CoV-2, and in South Korea alone, 30% of patients reported these symptoms.⁶ Otolaryngologists now suggest that anosmia could be a warning sign in patients with COVID-19, and they should undergo self-isolation to avoid the risk of spreading the disease.⁷

Through this report, we highlight the association of COVID-19 with anosmia and hypogeusia, so that health care professionals can promptly test the individuals for novel SARS-CoV-2 and manage them accordingly. As the number of cases are rising rapidly around the world, effective screening and diagnostic modalities can help infected individuals to self-quarantine and seek medical attention when required. We suggest a data-driven approach to understand the neurological manifestations and to predict the prognosis of anosmia in this ongoing pandemic as it is still unexplored and thus, can provide useful information regarding the disease course and help clinicians to chart the way forward.

Authorship statement

Saad Nasir and Pulwasha Maria Iftikhar designed the study. All the authors performed the study, contributed to data extraction, literature review, analyzed the data, and wrote the paper.