Olfactory Training as a Treatment for Olfactory Dysfunction Post COVID-19 (OTTODC19)

Olfactory dysfunction is a defining symptom of COVID-19 infection. Studies have demonstrated improved olfaction in patients with post infectious olfactory dysfunction after an olfactory training (OT). The aim of this study is to assess the clinical outcomes of olfactory training (12 weeks) therapy in the treatment of persistent olfactory dysfunctions after COVID-19. Specially, we aim to compare the effectiveness of two different olfactory training (different odors) with a placebo group. A group will train themselves with 4 scents (rose, orange, clove and eucalyptus) and another group with 4 different scents (cheese, coffee, strawberries and lemon). The placebo group will train themselves with an odorless substance. Olfaction sensory evaluation will be performed by using different olfaction tests (Sniffin' Sticks and UPSIT) and complete questionnaires to assess olfactory perception and particularly parosmia and phantosmia.

For 12 weeks, morning and evening, smell four odors namely eucalyptol, phenyl ethanol, Orange, and eugenol, for a total of five minutes per session.

For 12 weeks, morning and evening, smell four odors namely coffee aroma, cheese aroma, strawberries, and limon, for a total of five minutes per session.

For 12 weeks, morning and evening, smell four different odors or four odorless substances for a total of five minutes per session.

Changes from baseline in olfactory score on the University of Pennsylvania Identification Test (UPSIT) [ Time Frame: Measurement will be taken at time zero (pre-intervention) and 12 weeks (post-intervention)

The UPSIT includes 4 odor-impregnated booklets that contain 10 forced-choice multiple choice questions each for participants to scratch-and-sniff to identify various odors and is a commercially available test. Normosmia is defined as ≥34 for males and ≥35 for females, and a change of 4 points or more from baseline indicates a clinically meaningful result.

Sniffin' Sticks test and Taste strips: Sniffin' Sticks test (Burghardt®, Wedel, Germany) is a psychophysical test. It allows semi-objective assessment of the patient's olfactory performance by means of 3 subtests: threshold test, identification test and discrimination test. The Sniffin' Sticks Olfactory Test Kits contain pen like bodies as, for example, in pens used to write on flipcharts or whiteboards.These pen-like bodies, however, contain a fibre stick which is filled with scents. For testing, the cap should be removed so the patient can smell on the tip of the pen.

The TMSC is a 55-item questionnaire evaluating the three chemical senses: olfaction, taste and the trigeminal sense. First, questions with a 10-point visual analog scale make a subjective self-assessment of each of the three senses. Multiple-choice questions establish the precise characteristics of the dysfunctions of each of the senses if they are present. Secondly, a psychophysical test is administered remotely using substances typical of North American cuisines. Substances are first sniffed (peanut butter, jam, vinegar, coffee) then tasted (peanut butter, jam, salt water (1 tsp/250mL), sugar water (3 tsp/250mL)). The perceived intensity of each of the substances is reported each time on a visual analogue scale of 10 points.

This test has a first part with four questions that aim to assess the presence of parosmia or phastosmia. Patients who have reported parosmia or phantosmia will be asked to complete a second part with six questions focusing on the quality of their olfactory distortion.

The sQOD-NS is a validated questionnaire that measures the quality of life specific to olfactory functions. The questionnaire measures 7 items with a 4-point Likert scale.

A visual analog scale (scale from "not a problem" to "severe problem") is used by participants to assess their nasal obstruction. The duration of this test is approximately 2 minutes.

Inclusion Criteria: Patient diagnosed positive for COVID-19 with persistent olfactory dysfunction Willing and able to provide written informed consent Understand and read the French language Have an internet connection and a working email address Exclusion Criteria: Anosmia and hyposmia pre-covid-19 Be known chronic rhinosinusitis with or without nasal polyposis Have received radiotherapy or chemotherapy for Head and Neck Tumors Have a diagnosis of Alzheimer's, Parkinson's, multiple sclerosis or any other neurodegenerative disease 5. Have a brain tumor or ENT diagnosis 6. History of naso-sinus surgery; 7. History of traumatic brain injury