Olfactory evaluation in hospitalised and self-isolated patients with COVID-19: a single-centre experience on 55 cases

Smell loss is a common symptom of COVID-19 infection. Majority of the studies that evaluated olfactory impairment in COVID-19 used questionnaires (subjective smell evaluations) and did not compare the results with objective or semiobjective measures of smell. We performed smell testing in hospitalised and self-isolated patients with COVID-19 and control participants.

Fifty-five COVID-19 and 44 control participants underwent smell testing, using Burghart Sniffin' Sticks 'Screening 12 Test'. Participants also rated their smelling capability on the numerical scale. Differences between groups and correlation between smell loss and time from acute onset of symptoms were tested, as well as correlation between results of smell test and subjective assessment of smell.

Hospitalised patients with COVID-19 correctly determined 6.5/12 odorants compared with 10/12 in the self-isolated and 11/12 in the control group (p<0.001). Hyposmia or anosmia were present in 87.5% of hospitalised and 29.0% of self-isolated patients (p<0.001). The correlation between subjective self-assessment and results of smell testing was non-significant in both groups of patients with COVID-19, while there was a moderate positive correlation (p=0.001, Spearman's correlation coefficient=0.499) in control participants.

Contrary to some previous reports suggesting that the presence of olfactory loss may predict milder course of disease, our study found that a vast majority of hospitalised patients with COVID-19 had prominent olfactory impairment. The absence of correlation between self-rated and objective smell evaluation in patients with COVID-19 indicates that subjective smell assessment is unreliable.