Anosmia in SARS-CoV-2 Patients: a Retrospective Study

Background: Post viral anosmia has been reported in human coronavirus infections. In this current pandemic, olfactory dysfunction (OD) has emerged as a common key presenting symptom of COVID-19 infection. In this study, we describe OD assessment in the inpatient setting of patients both suspected of and with confirmed COVID-19 infection via University of Pennsylvania Smell Identification Test (UPSIT) objective assessment and a simple self-reported 3-item questionnaire. Methods: Thirty patients admitted to the isolation wards of the National University Hospital, Singapore for either suspected or confirmed COVID-19 infection from April to May 2020 were recruited to this study. 10 patients who tested negative for SARS-CoV-2 were recruited as control subjects. The 20 patients with COVID-19 infection were divided into two groups (10 had olfactory testing performed during the first week of illness, 10 in the second week of illness). A simple 3-question survey was administered to each participant - to rank the severity, state the onset and duration of their hyposmia. Olfactory testing was performed using an English version of the UPSIT. Results: Loss of smell was reported in 2 participants from the control group, 6 participants from the in the first week of illness and 5 participants from the second week of illness. Two COVID-19 patients have anosmia on the UPSIT. COVID-19 patients were more likely to have severe hyposmia or anosmia by objective assessment, a difference that was statistically significant ( P = 0.0485). The differences in degree of OD among COVID-19 patients in their first and second week of illness were not statistically significant ( P = 0.6563). Conclusion: Self-reported anosmia was higher among COVID-19 patients compared to controls who were admitted to isolation wards for respiratory symptoms but were tested negative for SARS-CoV-2 infection. On objective assessment by the UPSIT, COVID-19 patients were found to have higher rates of severe hyposmia or anosmia, a difference that was statistically significant ( P = 0.0485). A limitation of this study is the odorants used in UPSIT which may be less familiar to the primarily Asian participants in this study, owing to cultural differences.