Smell and Taste in Severe CoViD-19: Self-Reported vs. Testing

Abstract

One of the most striking reported symptoms in CoViD-19 is loss of smell and taste. The frequency of these impairments and their specificity as a potential central nervous system function biomarker are of great interest as a diagnostic clue for CoViD-19 infection as opposed to other similar symptomatologic diseases and because of their implication in viral pathogenesis. Here severe CoViD-19 was investigated by comparing self-report vs. testing of smell and taste, thus the objective severity of olfactory impairment and their possible correlation with other symptoms. Because a significant discrepancy between smell and taste testing vs. self-report results (p < 0.001) emerges in our result, we performed a statistical analysis highlighting disagreement among normosmia (p < 0.05), hyposmia, severe hyposmia, and anosmia (p < 0.001) and, in hypogeusia and severe hypogeusia, while no differences are observed in normogeusia and ageusia. Therefore, we analyzed the olfactory threshold by an objective test revealing the distribution of hyposmic (34%), severe hyposmic (48%), and anosmic (13%) patients in severe CoViD-19. In severe CoViD-19 patients, taste is lost in 4.3% of normosmic individuals, 31.9% of hyposmic individuals, 46.8% of severe hyposmic individuals, and 17% of anosmic individuals. Moreover, 95% of 100 CoViD-19 patients objectively tested were affected by smell dysfunction, while 47% were affected by taste dysfunction. Furthermore, analysis by objective testing also highlighted that the severity of smell dysfunction in CoViD-19 subjects did not correlate with age and sex. In conclusion, we report by objective testing that the majority of CoViD-19 patients report severe anosmia, that most of the subjects have olfactory impairment rather than taste impairment, and, finally, that the olfactory impairment correlate with symptom onset and hospitalization (p < 0.05). Patients who exhibit severe olfactory impairment had been hospitalized for about a week from symptom onset; double time has taken place in subjects with normosmia. Our results may be limited by the relatively small number of study participants, but these suggest by objective testing that hyposmia, severe hyposmia, and anosmia may relate directly to infection severity and neurological damage. The smell test assessment could be a potential screening symptom that might contribute to the decision to test suspected cases or guide quarantine instructions, further therapeutic approach, and evaluation of neurological damage.

Keywords: CoViD-19; anosmia; hyposmia; olfactory threshold; smell; smell test; taste.

Figure 1

Comparison between testing vs. self-report in CoViD-19, positive control, and negative control in smell (Right) and taste (Left). Significant discrepancy between smell testing vs. self-report, MANOVA p < 0.001 (for detailed statistic, see text).

Figure 2

Comparison of quantitative smell and taste test results in severe CoViD-19 patients and positive and negative controls. Significant differences occur between severe CoViD-19 patients and controls, MANOVA p < 0.001 (for detailed statistic, see text).

Figure 3

Comparison of quantitative smell and taste test results in severe CoViD-19 patients and positive and negative controls. The prevalence of smell impairments is clear; besides in CoViD-19, taste disturbances are present also in normosmia.

Figure 4

Olfactory threshold in severe CoViD-19 patients, positive and negative controls. A total of 95% of severe CoViD-19 patients show olfactory impairment in comparison to 75% of positive control and 22% of negative control. A detailed percentage for olfactory threshold is shown for CoViD-19 patients and positive and negative controls. Highlight of the prevalence of severe hyposmia in CoViD-19 patients, which is a characteristic compared to other smell-dysfunctional patients like the positive control that has a prevalence in hyposmia. Hyposmia and sever hyposmia are slightly present in negative controls—healthy subjects.

Figure 5

Olfactory threshold vs. age in severe CoViD-19 patients and positive and negative controls; no age correlation emerged.

Figure 6

Olfactory threshold vs. sex in severe CoViD-19 patients and positive and negative controls; no sex correlation emerged.

Figure 7

Olfactory threshold vs. symptom onset to hospitalization in severe CoViD-19 patients. The days from symptom onset to hospitalization between patients with normosmia vs. threshold impairment are statistical significant.