Changes in smell and taste perception related to COVID-19 infection: a case-control study

Abstract

The main aim of the present study was to psychophysically evaluate smell and taste functions in hospitalized COVID-19 patients and to compare those results with a group of healthy subjects. Another aim of the study was to assess the relationship of changes in patients' smell and taste functions with a number of clinical parameters, symptoms, and other physiological signs as well as with severity of disease. Olfactory and gustatory functions were tested in 61 hospitalized patients positive for SARS-CoV-2 infection and in a control group of 54 healthy individuals. Overall, we found a significant impairment of olfactory and gustatory functions in COVID-19 patients compared with the control group. Indeed, about 45% of patients self-reported complaints about or loss of either olfactory or gustatory functions. These results were confirmed by psychophysical testing, which showed a significantly reduced performance in terms of intensity perception and identification ability for both taste and smell functions in COVID-19 patients. Furthermore, gustatory and olfactory impairments tended to be more evident in male patients suffering from more severe respiratory failure (i.e., pneumonia with need of respiratory support need during hospitalization).

Figure 1

Mean intensity self-reported scores ± SEM of smell and taste functions of controls grouped by controls (CTRL, magenta bars) at the time of enrollment and cases (COVID) before (green bars) and during infection (light blue bars). Different letters indicate significant differences according to Mann–Whitney U test; P < 0.001).

Figure 2

Violin plots showing the differences in olfactory and gustatory assessments in controls (CTRL) and cases (COVID). The plots provide a representation of data distribution and the median ± IQR within each group for each smell and taste assessments. Statistics according to Mann–Whitney U test; ***P < 0.001).

Figure 3

Mean liking ± SEM for the individual odors grouped by controls (CTRL, magenta bars) and cases (COVID, green bars). Statistics according to t- test; **P < 0.01; ***P < 0.001).

Figure 4

Bi-plots from Principal Component Analysis with confidence ellipses (confidence level 95%) conducted on variables related to smell and taste measurements (Identification Smell Score, Intensity Smell Score, Irritation Smell Score, Identification Taste Score, Intensity Taste Score) obtained for COVID group (n = 61). Patients characterized by a low and high sensory performance are displayed in orange (LOW Perf) and blue (HIGH Perf), respectively.