Prevalence and recovery rate of persistent olfactory dysfunction in COVID-19: the COVORTS study

BACKGROUND: Olfactory dysfunction is a well-recognized symptom of COVID-19 infection. However, prevalence and recovery rate of these persistent symptoms differ across reports. Here, we report prevalence and recovery rate of psychophysically measured quantitative olfactory dysfunction, qualitative complaints, and subjective olfactory functioning up to 15 months after infection.

METHODOLOGY: The COVORTS cohort included 76 patients between 18-60 years with recent (1 month) olfactory dysfunction. The (extended) Sniffin' Sticks test was performed at baseline (T1), and 3 months, 6 months, 9 months, and 12 months later (T13). Monthly online questionnaires were completed on self-reported overall olfactory functioning and qualitative complaints.

RESULTS: Prevalence of quantitative olfactory dysfunction was 89.5% at baseline, and 69.1% at T13. Clinically relevant recovery was achieved by 29.4% of patients at T13. Prevalence of parosmia remained around 50%, while phantosmia slowly decreased from 43.4% to 23.5%. Subjective olfactory functioning slowly improved over time before levelling out at around half of pre-illness ability. At T13, 37.9% of patients reported an improvement of at least 80% of pre-COVID function. Fluctuations were observed within individuals for all three measurements.

CONCLUSIONS: Irrespective of measurement method, prevalence of olfactory dysfunction remains high up to 15 months after infection, and recovery rate is low. Individual fluctuations were observed between timepoints, indicating that recovery is not stable. Acknowledgement of symptoms, knowledge of fluctuations, and longer follow-up to evaluate further recovery are crucial to improve patient management.