Psychophysical assessment of olfactory and gustatory function in post‐mild COVID‐19 patients: A matched case‐control study with 2‐year follow‐up

Abstract

BackgroundThe aim of this study was to psychophysically evaluate the prevalence of smell and taste dysfunction 2 years after mildly symptomatic severe acute respiratory syndrome–coronavirus‐2 (SARS‐CoV‐2) infection compared to that observed at 1‐year follow‐up and while considering the background of chemosensory dysfunction in the no‐coronavirus disease 2019 (COVID‐19) population.MethodThis is a prospective case‐control study on 93 patients with polymerase chain reaction (PCR)‐positive SARS‐CoV‐2 infection and 93 matched controls. Self‐reported olfactory and gustatory dysfunction was assessed by 22‐item Sino‐Nasal‐Outcome Test (SNOT‐22), item “Sense of smell or taste.” Psychophysical orthonasal and retronasal olfactory function and gustatory performance were estimated using the extended Sniffin’ Sticks test battery, 20 powdered tasteless aromas, and taste strips test, respectively. Nasal trigeminal sensitivity was assessed by sniffing a 70% solution of acetic acid.ResultsThe two psychophysical assessments of chemosensory function took place after a median of 409 days (range, 366–461 days) and 765 days (range, 739–800 days) from the first SARS‐CoV‐2–positive swab, respectively. At 2‐year follow‐up, cases exhibited a decrease in the prevalence of olfactory (27.9% vs. 42.0%; absolute difference, −14.0%; 95% confidence interval [CI], −21.8% to −2.6%; p = 0.016) and gustatory dysfunction (14.0% vs. 25.8%; absolute difference, −11.8%; 95% CI, −24.2% to 0.6%; p = 0.098). Subjects with prior COVID‐19 were more likely than controls to have an olfactory dysfunction (27.9% vs. 10.8 %; absolute difference, 17.2%; 95% CI, 5.2% to 28.8%) but not gustatory dysfunction (14.0% vs. 9.7%; absolute difference, 4.3%; 95% CI, −5.8% to 14.4% p = 0.496) still 2 years after the infection. Overall, 3.2% of cases were still anosmic 2 years after the infection.ConclusionsAlthough a proportion of subjects recovered from long‐lasting smell/taste dysfunction more than 1 year after COVID‐19, cases still exhibited a significant excess of olfactory dysfunction 2 years after SARS‐CoV‐2 infection when compared to matched controls.

Shedding light on human olfaction: electrophysiological recordings from sensory neurons in acute slices of olfactory epithelium

“…Human olfaction has long been considered a neglected sense and the recent COVID-19 pandemic has highlighted the scarce knowledge we have of human olfactory physiology. The sudden and widespread olfactory loss experienced during the pandemic caught us unprepared, with many individuals struggling to recover their sense of smell [1][2][3][4][5][6][7] . Indeed, although the morphology of the human olfactory epithelium was well known, there was limited knowledge about the molecular and functional landscape of different cell types within the human olfactory epithelium.…”

It is necessary to assess olfactory and gustatory function in post covid‐19 patients, due to the omicron variant infection

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To the Editor:Boscolo-Rizzo et al 1 concluded that although a proportion of patients recovered from enduring smell/taste dysfunction more than 1 year after coronavirus disease 2019 (COVID-19), some cases still showed a noteworthy remaining olfactory dysfunction 2 years after severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection compared to matched normal subjects.Initial reports stated that the most frequent symptoms of COVID-19 infection were fever, cough, dyspnea, and myalgia or fatigue. 2,3 Several authors later described an association between COVID-19 and altered olfactory and taste functions.

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“…Boscolo-Rizzo et al 1 concluded that although a proportion of patients recovered from enduring smell/taste dysfunction more than 1 year after coronavirus disease 2019 (COVID-19), some cases still showed a noteworthy remaining olfactory dysfunction 2 years after severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection compared to matched normal subjects.…”

“…Evidence strongly supports the association of neurological involvement with the lethality of SARS-CoV-2 infection, and Omicron's severity and lethality are much lower than those of other previous variants. 13,24 Therefore, fulfilling a protocol like the one run by Boscolo-Rizzo et al, 1 but with patients who have suffered COVID-19 due to the Omicron virus variant, would provide new insights into the prevalence of smell and taste dysfunction in patients who suffered COVID-19.…”

Reply to: It is necessary to assess olfactory and gustatory functions in post‐COVID‐19 patients due to the omicron variant infection

“…This may place subjects at risk of exposure to environmental hazards. 4 Thus, a complete orthonasal evaluation of the olfactory function, including identification, discrimination, and threshold subtests, is crucial.…”