Investigation of the mechanisms of persistent SARS-CoV-2 associated olfactory dysfunction (OD) in patients with well-documented olfactory function. The investigators plan to collect olfactory cleft biopsies and cytobrushes in COVID-19 patients and controls.

An explorative prospective clinical study using human body materials of living post-COVID-19 patients with and without OD, to study the mechanisms of persisting olfactory dysfunction. Patients consult ENT specialist for medical purposes and undergo standard-of-care diagnostics and management. The collected tissues from the olfactory cleft mucosa will be analyzed using single cell RNA sequencing and RNAscope combined with immunohistochemistry.

Inclusion Criteria:

• Olfactory Dysfunction group: Presence of evident OD (Parosmia, Threshold-Discrimination-Identification (TDI)-score ≤24, Subjective abnormal quantitative olfactory function; measured by a visual analogue score (VAS) of smell impairment ≥5/10
• Control group: No OD (TDI-score >30.5.)

Exclusion Criteria:

• Presence of concomitant nasal mucosal pathology that might affect olfactory function or bias the study investigations
• Use of anticoagulation therapy
• Allergy to local anesthetics