Comparative Analysis of Olfactory and Gustatory Function of Patients With COVID-19 Olfactory Dysfunction and Non-COVID-19 Postinfectious Olfactory Dysfunction.

Background: Coronavirus disease 2019 (COVID-19) is known to have a high incidence of loss of smell and taste. However, studies in the early stages of the COVID-19 pandemic have evaluated these symptoms using subjective surveys and simple olfactory tests only. Hence, we compared the olfactory and gustatory characteristics of patient groups with COVID-19 olfactory dysfunction (C19OD) and non-COVID-19 postinfectious olfactory dysfunction (PIOD) using an objective olfactory test and evaluated the significance of olfactory training in both patient groups.

Methods: We retrospectively analyzed the medical records of 14 patients with a decreased sense of smell after having positive COVID-19 polymerase chain reaction results, and 56 patients with PIOD with no history of confirmed COVID-19. Participants were evaluated using the Korean version of the Sniffin' stick (KVSS) II, and chemical gustometry and olfactory training was assessed during their first visit. Olfactory training was then re-evaluated after an average of 8 (± 6) weeks.

Results: The average age of participants in the C19OD group was lower than in those in the non-COVID-19 PIOD group. The proportion of men in the C19OD group was higher than in the non-COVID-19 PIOD group. At baseline assessment, the C19OD group had better olfactory and gustatory functions. After olfactory training, the non-COVID-19 PIOD patient group showed a significant increase in all KVSS II Total, T, D, and I scores, but there was a non-significant increase in all scores in the C19OD group.

Conclusion: The C19OD group had better olfactory and gustatory function than the non-COVID-19 PIOD group at the initial assessment. After olfactory training, there was an increase in olfactory function test scores in both groups. Olfactory training may be helpful in C19OD, as in non-COVID-19 PIOD.