Physiological discrimination and correlation between olfactory and gustatory dysfunction in long-term COVID-19

The spread of the SARS-CoV-2 virus produces a new disease termed COVID-19, the underlying physiological mechanisms of which are still being understood. Characteristic of the infection is the compromising of taste and smell. There is a persistent need to discriminate the dysfunctions and correlation between taste and smell, which are probably epiphenomena of other concealed conditions. Anosmic and ageusic long-term COVID-19 patients were re-evaluated after 1 year using a Volabolomic approach with an e-nose recording system coupled with olfactometric and gustometric tests. Here a range of sensory arrangements was found, from normal taste and smell to complete losses. The following patterns of olfactory threshold (OT)-taste threshold-olfactory uni- and cross-modal perception were found anosmia-severe hypogeusia-anosmia; hyposmia-hypogeusia-severe hyposmia; normosmia-ageusia-hyposmia; severe hyposmia -normogeusia-normosmia. There is a strong correlation between OT and olfactory uni- and cross-modal perception, a moderate correlation between olfactory and taste threshold and no correlation between OT and taste threshold. In conclusion, this study provides evidence for the feasibility of testing the chemical senses to directly objectify function in order to discriminate taste from olfactory impairment. Furthermore, it allows to hypothesize a long-term effect of the virus due to neuroinvasion through, probably, the olfactory system with injury in the related multisensory areas of taste and smell.