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

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.