Impairments in odour detection and hedonic ratings of unpleasant smells in asymptomatic university students as SARS‐Cov‐2 emerged locally

Abstract

Sudden olfactory loss in the absence of concurrent nasal congestion is now a well‐recognized symptom of COVID‐19. We examined olfaction using standardized objective tests of odour detection, identification and hedonics collected from asymptomatic university students before and as SARS‐CoV‐2 emerged locally. Olfactory performance of students who were tested when the virus is known to be endemic (n = 22) was compared to students tested in the month prior to viral circulation (n = 25), a normative sample assessed during the previous 4 years (n = 272) and those tested in prior years during the same time period. Analyses showed significantly reduced odour detection for the virus exposed cohort compared to students tested before (t = 2.60; P = .01; d = 0.77; CI 0.17, 1.36) and to the normative sample (D = 0.38; P = .005). Odour identification scores were similar, but the exposed cohort rated odours as less unpleasant (P < .001, CLES = 0.77). Hyposmia increased 4.4‐fold for students tested 2 weeks before school closure (N = 22) and increased 13.6‐fold for students tested in the final week (N = 11). While the unavailability of COVID‐19 testing is a limitation, this naturalistic study demonstrates week‐by‐week increase in hyposmia in asymptomatic students as a virus was circulating on campus, consistent with increasing airborne viral loads. The specific hedonic deficit in unpleasantness appraisal suggests a deficit in the TAAR olfactory receptor class, which conveys the social salience of odours. Assessment of odour detection and hedonic ratings may aid in early detection of SARS‐CoV‐2 exposure in asymptomatic and pre‐symptomatic persons.

A study on the relationship between odor hedonic ratings and individual odor detection threshold

“…Yet, several studies showed a great flexibility of odor hedonic perception. Thus, differences were observed in relation to individual characteristics such as age 10 – 12 , sex 13 – 18 , the experience towards odorants 19 and physiological state 20 , 21 , diseases such as depressive disorders 22 , schizophrenia 23 , 24 or Parkinson’s disease 25 , 26 and recently with SARS-CoV-2 27 . Odor hedonic perception also appeared to depend on repeated exposures 28 , 29 , verbal influence 30 , 31 , or stimulus presentation pathway (orthonasal vs. retronasal) 32 .…”