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Persistence of Loss of Smell After Mild COVID-19 Varies Significantly

Is there a pharmacist out there who hasn’t been asked by a recovering COVID-19 patient: When will I get my sense of smell (and taste) back? Now, a new European study provides some answers. Find out what likely causes olfactory dysfunction and how long it can last.

MARSEILLE, FRANCE – Olfactory dysfunction is extremely common in mild COVID-19 but less so in those with moderate and severe-to-critical cases, according to a new study.

The report in the Journal of Internal Medicine examined prevalence of problems with smelling and recovery in patients with varying degrees of severity of COVID-19.

In the study of 2,581 patients from 18 European hospitals, French-led researchers determined that the patient-reported prevalence of olfactory dysfunction was 85.9% in mild cases of COVID-19, 4.5% in moderate cases, and 6.9% in severe-to-critical cases.

The study team also advises that the average duration of olfactory dysfunction reported by patients was 21.6 days, although almost a fourth of patients hadn’t recovered their sense of smell after 60 days. More than a third of patients reported smell recovery within the 14 days following the development of OD, but one third did not recover within the 45 days, according to the article.

The authors add that objective clinical evaluations identified olfactory dysfunction in 54.7% of mild cases of COVID-19 and 36.6% of moderate-to-critical cases of COVID-19. At 60 days and 6 months, 15.3% and 4.7% of these patients did not objectively recover their sense of smell, respectively.

"Olfactory dysfunction is more prevalent in mild COVID-19 forms than in moderate-to-critical forms, and 95% of patients recover their sense of smell at 6-months post-infection," said lead author Jerome R. Lechien, MD, PhD, MS, of Paris Saclay University.

For the study, from March 22 to June 3, 2020, 2,581 COVID‐19 patients were identified from 18 European hospitals.

Researchers also advise that the higher baseline severity of objective olfactory evaluations was strongly predictive of persistent olfactory dysfunction, adding, “OD is more prevalent in mild COVID‐19 forms than in moderate‐to‐critical forms. OD disappeared in 95% of patients regarding objective olfactory evaluations at 6 months.”

According to the authors, high prevalence of OD in COVID‐19 patients “supports the need for primary care, ear, nose and throat (ENT) and neurology physicians to be able to counsel patients regarding the likelihood of recovery, and to identify those at risk of persistent OD, such that therapeutic strategies can be targeted appropriately. “

The authors suggest that, in addition to the more common reason of nasal congestion, OD could be linked to the injury of the olfactory neuroepithelial and spread of the virus into the olfactory bulb, where sustentorial cells and stem neurons may express ACE2 and TMPRSS2. The longer duration of OD in some patients could be due to higher protein expression and more extensive injuries of the olfactory cells, they posit.

“In sum, the mechanisms underlying the OD development could associate olfactory cleft congestion in short‐term anosmic patients, injury of the olfactory neuroepithelium and virus spread into the olfactory bulb in mid‐to‐long‐term anosmic patients. Future studies are needed to confirm these hypotheses,” the researchers conclude.