Gaining back what is lost: recovering the sense of smell in mild to moderate patients after COVID-19

The purpose of our cohort study was to quantify olfactory deficits in COVID-19 patients using Sniffin' Sticks and a pre-post design to evaluate olfactory recovery. 30 adult patients with laboratory-confirmed mild to moderate forms of COVID-19 underwent a quantitative olfactory test performed with the Sniffin' Sticks Test (SST, Burghardt®, Wedel, Germany) considering olfactory threshold (T), odor discrimination (D) and odor identification (I). Results were presented as a composite TDI score (range 1-48) used to define functional anosmia (TDI ≤ 16.5), hyposmia (16.5 < 30.5) or functionally normal ability to smell (TDI ≥ 30.5). Patients also self-evaluated their olfactory function by rating their ability to smell on a visual analogue scale (VAS rating) and answering a validated Italian questionnaire (Hyposmia Rating Scale-HRS). Patients were tested during hospitalization and about two months after symptoms onset. During the hospitalization the overall TDI score indicated that our cohort had impairments in their olfactory ability (10 % was diagnosed with Anosmia and more than 50 % were hyposmic). Almost all patients showed a significant improvement at around one month following the first test and for all the parts of the SST except for odor identification. None of the subjects at one month was still diagnosed with Anosmia. We also quantified the improvement in the TDI score based on initial diagnosis. Anosmic subjects showed a greater improvement than hyposmic and normosmic subjects. In conclusion, within a month time window and two months after symptoms' onset, in our cohort of patients we observed a substantial improvement in the olfactory abilities.