Sniffing out Covid - 'COVORTS study: the COVid cohORT on Smell loss', 'long COVORTS: the COVid cohORT on long-term Smell Loss' and 'Imaging smell loss in Covid-19: an (f)MRI approach'

1. COVORTS study: the COVid cohORT on Smell loss.
The goal of the COVORTS study was to evaluate the course of persistent COVID-19-related chemosensory dysfunction over time and its effects on quality of life and eating behaviour. 76 patients with persistent (>1 month) self-reported olfactory dysfunction after recent (<3 months) SARS-CoV-2 infection (confirmed with a positive PCR-test, or a positive SARS-CoV-2-antigen self-test) aged 18-60 were included. 74 patients signed consent for data sharing. Patients were followed for a period of one year. Measurements involved a monthly online questionnaire (Timepoints T1-T13), and a home visit from a researcher every three months (T1, T4, T7, T10 and T13). Measurements in the monthly questionnaire involved: demographics; self-reported olfactory (including the presence of parosmia and phantosmia symptoms), gustatory and trigeminal perception; the Appetite, Hunger and Sensory Perception (AHSP) questionnaire; the (English) Olfactory Disorders Questionnaire (eODQ); and the home test of the GCCR Smell-&-Taste-Check. Measurements during the home visits involved: the Sniffin’ Sticks test battery (including the extended version of the Identification subtest); the Sniffin’ Sticks Parosmia Test (SSParoT); the Taste Strips test and the SCENTinel (the latter was added at a later stage of the study duration, so not all patients have completed this test). Please note that apart from the first measurement T1 (when the questionnaire was completed in the presence of a researcher), the measurements from the questionnaire and the home visits did not always occur on the same day, even if they have the same timepoint value. The questionnaire was completed by patients at a time convenient to them, and we do not have access to exact completion dates for each participant. More details on methodology, data-analysis and results can be found in: https://doi.org/10.1016/j.nutos.2024.05.003; https://doi.org/10.4193/rhin24.331; and https://doi.org/10.1016/j.appet.2025.108391.

2. long COVORTS: the COVid cohORT on long-term Smell Loss.
The goal of the long COVORTS study is to evaluate the (subjective) course of persistent COVID-19-related chemosensory dysfunction over time and its effects on quality of life and eating behaviour. In this study, ~150 patients who are within 12 months of their SARS-CoV-2 infection (confirmed with a positive PCR-test, or a positive SARS-CoV-2-antigen self-test) and who have at least six months self-reported chemosensory dysfunction following their COVID-19 infection aged 18-60 will be included. Patients are followed for a period of one year. Measurements involved a monthly online questionnaire every three months T1-T5). Measurements in the questionnaire involve: demographics; self-reported olfactory (including the presence of parosmia and phantosmia symptoms), gustatory and trigeminal perception; the Appetite, Hunger and Sensory Perception (AHSP) questionnaire; the (English) Olfactory Disorders Questionnaire (eODQ); and the home test of the GCCR Smell-&-Taste-Check. Data will be published upon project completion.

3. Imaging smell loss in Covid-19: an (f)MRI approach.
The goal of this (f)MRI approach is to evaluate how persistent COVID-19-related olfactory dysfunction affects the brain functionally and structurally, and possibly elucidate the neural mechanism behind these symptoms and their progression over time. 50 patients with persistent COVID-19-related olfactory dysfunction (confirmed with a positive PCR-test, or a positive SARS-CoV-2-antigen self-test) aged 18-60 will included. Two subgroups will be made: 25 patients with anosmia or hyposmia (based on the Sniffin’ Sticks test battery) and 25 patients with parosmia (self-reported). These patients will be partly included from the COVORTS study cohort, others will be recruited solely for this (f)MRI sub-study. Imaging includes anatomical scans involving a coronal T2-weighted scan of the olfactory bulbs and whole-brain anatomical scan using high-resolution T1-weighted 3D TFE. Furthermore, functional (BOLD fMRI) scans with odour-exposure to two odours (chocolate and beef) will be performed using a T2-weighted gradient echo 2D-EPI sequence. Patients who had their first MRI session within six months of their SARS-CoV-2 infection will have a follow-up scan after their first session. Data on demographics, Sniffin’ Sticks test score, olfactory bulb volume, total intracranial volume, total grey and white matter and cerebrospinal fluid volumes, and grey matter volumes of olfactory-related regions will be published upon project completion.