The present study aims to describe the structural tissue and cell characteristics of the olfactory mucosa in patients with persistent anosmia (≥2 years) due to COVID-19 or head-trauma, in comparison to healthy individuals with intact olfactory function. In order to avoid possible age-related degenerative changes in the neuro-epithelium, both patients and controls are between 25 and 35 years of age.

Inclusion Criteria:

• Legally competent to vouch for their own study participation.

• Informed and written consent for participation in this study.

• Study group 1 (Post-COVID anosmia)

  1. Diagnosed with persistent anosmia for approximately two years concurring with positive SARS-CoV-2 PCR-test between 2019 and 2020.
  2. Sniffin'sticks test with a threshold-discrimination-identification-score(TDI)≤16
  3. Between 25 and 35 years of age.

Study group 2 (Post-trauma anosmia)

1. Diagnosed with persistent anosmia for approximately two years concurring with head trauma.
2. Sniffin'sticks test with a threshold-discrimination-identification-score(TDI)≤16
3. Between 25 and 35 years of age.

Study group 3 (Controls):

1. Between 25 and 35 years of age.
2. Undergoing reposition of a nasal fracture in general anaesthesia

Exclusion Criteria:

• <25 years of age.

• >35 years of age.

• Chronic rhinosinusitis with/without polyps.

• Nasal cancer.

• Presence of viral or bacterial rhinosinusitis.

• Uncontrolled allergic rhinosinusitis.

• Coagulation deficiencies, e.g. haemophilia.

• Use of anticoagulants.

• Not able to undergo general anaesthesia.

• Pregnancy.

• Any use of nasal detumescence drugs ≤2 weeks before biopsy.

• Any use of nasal steroids ≤3 months before biopsy.

• Use of nasal inhaled recreational drugs ≤3 month before biopsy.

• Participants not able to communicate in Danish or English.

• Major Depression Inventory (MDI) score ≥27 [49, 50]

• Mini Mental State Examination (MMSE) score ≤ 26 [51]

• Study group 1 (Post-COVID anosmia)

  1. Anosmia for less than two years or more than two and a half years.
  2. No positive SARS-CoV-2 PCR-test concurring with olfactory dysfunction.
  3. History of olfactory dysfunction before COVID-19 infection.

• Study group 2 (Post-trauma anosmia)

  1. Anosmia for less than two years or more than approximately two-three years.
  2. Anosmia without concurring with head trauma
  3. History of prior olfactory dysfunction before head trauma.

• Study group 3 (Controls) 1. Known olfactory dysfunction.

recruited from the clinic