Self‐reported olfactory loss in COVID‐19: is it really a favorable prognostic factor?

We read with great interest the recent study by Yan et al. ¹ Based on data collected from the medical records of 169 coronavirus disease 2019 (COVID‐19) patients, the authors reported that the presence of chemosensitive disorders is significantly related to the development of milder forms of COVID‐19. Moreover, the authors suggest that these findings may allow the lay public and healthcare workers to stratify patients at risk of severe disease and in need of admission, while conserving healthcare resources by identifying those suitable for outpatient care. Their article had significant resonance and was reported widely by the American media. The suggestion that the presence of chemosensitive disorders can reassure patients as predicting a milder clinical course certainly has a strong appeal to a lay public deeply concerned about the current pandemic. However, we believe that, in times of great uncertainty, caution is needed before disseminating information that can influence people's healthcare‐seeking behavior.

Chemosensitive disorders appear to be frequent and often early symptoms of COVID‐19, but their prognostic value has not yet been clarified. Certainly, the prevalence of self‐reported loss of sense of smell or taste varies between studies of mild to moderate or severe disease. ² However, published studies are mostly anamnestic and, as Yan and coauthors suggest, these may be prone to recall bias, with underreporting of loss of smell or taste in the presence of severe respiratory disease. Emerging studies based on objective evaluation of patients in fact suggest that there is no significant correlation between the prevalence of chemosensitive disorders and COVID‐19 severity, supporting this proposal. ³ , ⁴ , ⁵ Furthermore, in our recent analysis of a series of 345 cases, patients with a duration of chemosensitive symptoms of >7 days had a 2.33‐fold greater risk of developing severe symptoms. ⁵ We also demonstrated how anamnestic data collection underestimates the frequency of chemosensitive disorders detected in psychophysical tests, particularly in patients with a more serious presentation. It seems likely that these patients have the same prevalence of chemosensitive dysfunction as patients with mild and moderate forms but neglect these symptoms while suffering with and receiving supportive treatment for severe respiratory disease.

On the basis of the objective data now emerging in the literature, we believe that, at present, it is not possible to affirm that olfactory and gustatory disturbances predict a milder course of COVID‐19. The public should certainly be informed that chemosensitive disorders are frequent and often early symptoms of disease, which may present in paucisymptomatic forms. For this reason, the sudden reduction of smell and taste, especially if not associated with rhinitis symptoms and nasal obstruction, should be considered as highly suggestive of SARS‐CoV‐2 infection. However, patients and the healthcare system should in no way neglect a deteriorating clinical picture and preclude admission due to false reassurance by the presence of chemosensitive dysfunction. Although in many cases of COVID‐19 smell and taste‐and‐smell disorders are short‐lived, persistence of chemosensitive dysfunction, possibly linked to a long‐lasting viral multiplication in the upper aerodigestive tract, may associate with a more severe clinical course.