Prevalence and 24-month recovery of olfactory dysfunction in COVID-19 patients: A multicentre prospective study

Objective To investigate the prevalence and recovery of olfactory dysfunction (OD) in COVID-19 patients 24 months after the infection. Methods From 22 March 2020 to 5 June 2022, 251 COVID-19 patients were followed in three European medical centres. Olfactory function was assessed with subjective patient-reported outcome questionnaires and odour identification tests at baseline, 6, 12, 18 and 24 months postinfection. The predictive values of epidemiological and clinical data were investigated with multivariate analysis. Results One hundred and seventy-one patients completed the evaluations. The odour identification test revealed that 123 patients (50.8%) had OD at baseline. The prevalence of persistent psychophysical abnormalities at 6, 12, 18 and 24 months post-COVID-19 was 24.2%, 17.9%, 5.8% and 2.9%, respectively (p = 0.001). Parosmia occurred in 40 patients (23.4%) and lasted 60 +/- 119 days. At 2 years, 51 patients (29.8%) self reported that their olfaction was unnormalised. Older patients had better odour identification evaluations at baseline (p < 0.001) but those with OD reported lower odour identification test scores at the end of the follow-up. Parosmia occurred more frequently in young patients. The olfactory training was significantly associated with higher values of Sniffin' Sticks tests at 18 months postinfection (r(s) = 0.678; p < 0.001). Conclusion Two years post-COVID-19, 29.8% of patients reported persistent OD, but only 2.9% had abnormal identification psychophysical evaluations.