Comparative analyses of COVID-19-related olfactory dysfunction and classical post-viral olfactory dysfunction: a...

Olfactory dysfunction (OD) is a common symptom of COVID-19. However, prevalence and clinical characteristics of OD due to COVID-19 (COVID-19-OD) differ from those of conventional post-viral OD (PVOD). Even among COVID-19-OD cases, they vary depending on the virus subtype. We aimed to compare the differences between COVID-19-OD and PVOD, as well as the differences across viral variants within COVID-19-OD.

This is a multicenter retrospective study. The subjects were PVOD patients from 2017 to 2019 and COVID-19-OD patients from 2020 to 2022. Patient backgrounds, olfactory cleft condition, and olfactory function were obtained from medical records and compared.

Of the 649 patients, 269 had COVID-19-OD (pre-Omicron: 191; Omicron: 78) and 380 had PVOD. Compared to the PVOD group, the COVID-19-OD group was younger and exhibited a higher rate of olfactory cleft obstruction and a greater prevalence of parosmia or phantosmia. The severity of OD was milder in the COVID-19-OD group. Even after controlling for age, the severity of OD remained milder in the COVID-19-OD group. Compared to the Omicron group, the pre-Omicron group was younger and had a higher incidence of parosmia or phantosmia.

COVID-19-OD and PVOD differ significantly in clinical features and in the pathophysiology of OD. Moreover, even within COVID-19-OD, there are differences between the variants, which are thought to reflect biological differences in the virus.