Olfactory Dysfunction Among Asymptomatic Patients with SARS CoV2 Infection: A Case–Control Study

Abstract

Olfactory dysfunction (hyposmia, anosmia) is a well-recognized symptom in patients with coronavirus disease-19 (COVID-19). Studies of olfactory dysfunction in asymptomatic patients have not been reported. We conducted a study looking for the presence of olfactory dysfunction with an objective assessment tool in asymptomatic Covid 19 and compared it with patients with mild COVID-19 and age-matched controls. We recruited 57 male patients each of Mild COVID-19, asymptomatic Covid 19, and healthy controls for the study. All participants underwent evaluation of smell threshold by Butanol Threshold test (BTT) and ability to distinguish common odors by Smell identification test. The scores of each test were recorded on a numerical scale. The participants in all three arms were matched for age, history of smoking, and pre-existing medical conditions. The mean scores of the Butanol Threshold test in Mild COVID-19, asymptomatic Covid 19 and controls were 2.95 ± 2.25 (0–7.5), 3.42 ± 2.23 (0–7.5), and 4.82 ± 1.86 (0–8), respectively. A one-way ANOVA showed a significant difference between groups (df 2, MS 53.78, F 11.94, p < 0.005). Intergroup differences using the student T-test showed significantly low BTT scores in Mild COVID-19 ( p < 0.005) and asymptomatic ( p < 0.005) as compared to control. BTT scores could not distinguish between asymptomatic patients and control. The smell threshold was impaired in asymptomatic Covid 19 and Mild COVID-19. Butanol Threshold Test score could not differentiate between asymptomatic Covid 19 and controls.

Self‐reported olfactory and gustatory dysfunction and psychophysical testing in screening for COVID‐19: A systematic review and meta‐analysis

“…A total of 2113 abstracts were retrieved for screening, 114 full‐text articles were assessed for eligibility, and 50 studies 7 , 8 , 9 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 meeting inclusion criteria were selected in the qualitative synthesis. Data from 49 studies 7 , ...…”

“…Table 1 presents the characteristics of included studies. 7 , 8 , 9 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 There were 16 case‐control studies 21 , 22 , …”

“…There were 4 olfactory identification tests with different numbers and types of odors. 7 , 9 , 44 , 52 Two studies reported use of olfactory threshold testing with ethanol 8 and 1‐butanol solutions. 44 One study 44 used an identification test to assess gustatory sensations of sweet and salty.…”

“… 7 , 9 , 44 , 52 Two studies reported use of olfactory threshold testing with ethanol 8 and 1‐butanol solutions. 44 One study 44 used an identification test to assess gustatory sensations of sweet and salty. Mangal et al reported 2 tests without cutoff and dichotomous data for extracting data.…”

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

“…Discerning the mechanism for the earliest changes in olfaction may be a key to early detection of SARS‐CoV‐2 infection. While self‐monitoring for smell loss is cost‐effective and easily implemented, research findings suggest that objective psychophysiological tests are more sensitive to COVID‐19 associated olfactory impairment than self‐report methods (Bagnasco et al, 2021; Gözen et al, 2020; Vaira et al, 2021) even in asymptomatic cases (Mangal et al, 2021; Vaira, Hopkins, et al, 2020). For example, a large multicenter study found that significantly more COVID‐19 positive participants were classified with olfactory dysfunction when tested with psychophysiological tests compared to self‐reported impairment (Vaira et al, 2021).…”