Evaluation of olfactory dysfunction persistence after COVID-19: a prospective study

Alterations of the olfactory function in patients affected by COVID-19 often have an early onset and a variable duration ranging from a few weeks to months. The aim of this study was to evaluate olfactory dysfunction persistence after recovery from COVID-19, and potential related clinical-demographic conditions.

A total of 76 patients recovered from COVID-19 from at least 20 days with olfactory dysfunction during the infection were included in the study. For the subjective evaluation of olfactory function, a visual analogic scale (VAS) was used. The objective evaluation was performed with the use of the Sniffin' Sticks test.

Objective assessment of olfactory function revealed that 48 (63.16%) patients were found to be normosmic (TDI ≥ 30.5), 26 (34.21%) were hyposmic (TDI from 30.5 to 16.5) and two (2.63%) were anosmic (TDI ≤ 16.5) at the time of the evaluation. These results did not show a significant difference between subjective and objective tests (p = 0.45). Most patients recovered their sense of smell within the first two months after recovery while a portion (22.2%) still experienced olfactory alterations 4-6 months after SARS-CoV-2 infection. Patients who had not recovered their sense of smell had a significantly longer period of SARS-CoV-2 positivity compared to patients that fully recovered (36.07 ± 7.78 days vs. 29 ± 7.89 days; p = 0.04).

Our results suggest that the duration of the infection negatively correlates with the recovery of olfactory function.