Study population
This study was approved by institutional review boards of the CHU Saint-Pierre, Brussels, Belgium, CHUSP210207 and of Epicura Hospital, Baudour, Belgium, P2020011. From October 2020 to November 2020 patients with a diagnosis of COVID-19 and olfactory dysfunction (OD) confirmed by psychophysical tests were recruited after 2 weeks of onset of symptoms at the Epicura Hospital, in Belgium. SARS-CoV-2 infection was diagnosed by nasal swabbing and reverse transcriptase polymerase chain reaction (RT-PCR). Symptoms were evaluated during the clinical course of the disease with the COVID-19 Symptom Index7. Subjective olfactory functions were evaluated with the smell and taste component of the National Health and Nutrition Examination Survey12. Fourteen to 15 days after onset of OD, patients were invited to perform a sniffing test and to donate blood and nasal secretion samples (nasal washing with physiological saline solution was carried out and nasal secretions were sterile aspirated). Subjects were categorized into anosmic, hyposmic and normosmic based on their Sniff Test. Psychophysical olfactory assessments were performed with the identification component of Sniffin’ Sticks tests (Medisense, Groningen, Netherlands), which is a validated psychophysical olfactory test using 16 smell pens. The final score ranges from 0 (none correctly identified) to 16 (all correctly identified). Normative values established normosmia as a score ranging between 12 and 16, hyposmia between 9 and 11 and anosmia between 0 and 813. It must be emphasized that at that time COVID-19 infections were associated with significant mortality and vaccines were not available; it is for this reason that only the identification part of the TDI was carried out to reduce the risk of contamination of the research team.
Inclusion criteria consisted of adults with SARS-CoV-2 infection identified through nasal swabs and positive RT-PCR and COVID-19 related OD. Patients with a history of pre-COVID-19 pandemic OD, chronic or self-reported acute rhinosinusitis (with regard to the European Position Paper on Rhinosinusitis and Nasal Polyps guidelines) and dementia at the time of evaluation were excluded. Socio-demographic and clinical data were collected through a standardized online questionnaire or medical records.