Factors Associated With Persisting Olfactory Dysfunction After COVID-19

Background

Fortunately, the majority of COVID-19 patients recover from olfactory dysfunction (OD) within the first couple of weeks. However, from approximately 5% up to 20% continue to suffer from OD even more than 1 year after the onset. Nonetheless, factors associated with long-lasting OD are hardly known. The aim of this study was to identify favourable and disadvantageous markers of persisting OD in COVID-19 patients.

Methodology

Sixty-six patients (46 female; mean age: 39.9 years) that suffer from OD longer than 6 months due to laboratory-confirmed SARS-CoV-2 infection have participated in this longitudinal study. Participants completed comprehensive psychophysical chemosensory tests (i.e., Sniffin' Sticks = TDI) and questionnaires twice at our department—on average 219 ± 80 (T-1) and 489 ± 89 (T-2) days after the onset of symptoms, respectively. Olfactory recovery rates were associated with demographic factors and questionnaires using linear regression analysis.

Results

Patients below 40 years of age improved better (TDI: 4.1 ± 4.3 vs. 0.7 ± 5.8; p = 0.008) and achieved statistically significant higher scores (TDI: 31.5 ± 4.0 vs. 27.3 ± 6.7; p = 0.033) regarding psychophysical chemosensory tests. Furthermore, linear regression analysis revealed that parosmia was associated with worse orthonasal smell function (T-1: β = −0.346, p = 0.004; T-2: β = −0.384, p = 0.001), especially concerning identification subtest (T-1: β = −0.395, p = 0.001; T-2: β = −0.398, p < 0.001). Moreover, increasing parosmia between T-1and T-2 led to worse orthonasal olfactory function (β = −0.294, p = 0.016).

Conclusions

Older age and parosmia seem to be unfavourable factors of persisting OD in COVID-19 patients.