A comparative analysis of the incidence, severity and duration of smell and taste loss in COVID-19 cases versus non-COVID-19 cases: a longitudinal cohort study.

Background: the COVID-19 pandemic has highlighted the relevance of olfactory and gustatory disorders. However, these symptoms can also be caused by various other factors. In this study we aim to compare the incidence, severity and duration between COVID-19 related and non-COVID-19 related smell and taste disorders. 

Methods: we conducted a longitudinal cohort study using data from the Dutch biobank Lifelines, which includes over 167,000 participants. The data were collected from 27 questionnaires distributed between March, 2020, and May, 2022. Descriptive data and the incidence of smell and taste loss in both groups was calculated. To visualize the proportion of severity rates of symptoms, a heatmap was created. A survival analysis was conducted and presented in a reversed  Kaplan-Meier curve to show the probability of having persisting smell loss in both groups.  

Results: the study included 235,722 participants, with a median age of 56 years. 5.5% reported to experience smell loss at least once, while 40.9% reported to never experience smell loss. The incidence of smell loss was higher in the COVID-19 positive group when compared to the COVID-19 negative group. We found varying degrees of symptom severity in COVID-19 positive cases, ranging from mild to severe, while non-COVID-19 related cases mostly reported mild symptoms. The survival outcome for smell and taste loss was 0.12 (SE 0.03, 95% CI 0.07-0.21) in cases related to COVID-19, and was 0.17 (SE 0.03, 95% CI 0.12-0.24) in cases related to other causes. 

Conclusion: this study reveals a higher incidence and severity of smell and taste loss in individuals with COVID-19 compared to non-COVID-19 related cases. However, non-COVID-19 related smell and taste loss tend to have a longer duration.