Olfactory training and visual stimulation assisted by web-application in patients with persistent olfactory dysfunction after SARS-CoV-2 infection: observational study.

Background: Persistent olfactory dysfunction (OD) is a significant complication of SARS-CoV-2 infection. Olfactory training (OT) using aromatic oils are recommended to improve olfactory recovery, but quantitative data are missing. Objective: We aimed to quantify the benefit of OT associated with visual stimulation assisted by a dedicated web-application on patients with 1-month or more OD. Methods: We performed an observational real-life data-based study on a cohort of patients with at least 1-month persistent OD included between 1/30/21 and 3/26/2021. Analysis was performed after a 4-weeks mean time of OT and at least 500 patients assessable for primary outcome. Participants exposed themselves twice daily to odors from four high concentration oils and visual stimulation assisted by a dedicated web-application. Improvement was defined as a 2/10 points increase on self-assessed olfactory visual analogue scale. Results: 548 were assessable for primary outcome assessment. The mean baseline self-assessed olfactory score was 1.9/10 (SD 1.7) and increase to 4.6 (SD 2.8) beyond a mean time of olfactory training of 27.7 days (SD 17.2). Olfactory training was associated with at least 2-points increase in 64.2% (n=352). The rate of patients with improvement was higher in patients having trained for more than 28 days versus patients having trained for less than 28 days (72.2% vs 59.0% respectively, p=.002). The kinetic of improvement was 8 days faster in hyposmic than in anosmic patients (p<.001). The benefit was observed regardless of the duration of the OD. Conclusions: OT associated with visual stimulation assisted by a dedicated web-application was associated with significant improvement in olfaction, especially if OT duration was superior to 28 days.