Analysis of Prevalence and Predictive Factors of Long-Lasting Olfactory and Gustatory Dysfunction in COVID-19 Patients

Abstract

Background: Although smell and taste disorders are highly prevalent symptoms of COVID-19 infection, the predictive factors leading to long-lasting chemosensory dysfunction are still poorly understood.

Methods: 102 out of 421 (24.2%) mildly symptomatic COVID-19 patients completed a second questionnaire about the evolution of their symptoms one year after the infection using visual analog scales (VAS). A subgroup of 69 patients also underwent psychophysical evaluation of olfactory function through UPSIT.

Results: The prevalence of chemosensory dysfunction decreased from 82.4% to 45.1% after 12 months, with 46.1% of patients reporting a complete recovery. Patients older than 40 years (OR = 0.20; 95% CI: [0.07, 0.56]) and with a duration of loss of smell longer than four weeks saw a lower odds ratio for recovery (OR = 0.27; 95% CI: [0.10, 0.76]). In addition, 28 patients (35.9%) reported suffering from parosmia, which was associated with moderate to severe taste dysfunction at the baseline (OR = 7.80; 95% CI: [1.70, 35.8]). Among the 69 subjects who underwent the UPSIT, 57 (82.6%) presented some degree of smell dysfunction, showing a moderate correlation with self-reported VAS (r = -0.36, p = 0.0027).

Conclusion: A clinically relevant number of subjects reported persistent chemosensory dysfunction and parosmia one year after COVID-19 infection, with a moderate correlation with psychophysical olfactory tests.

Keywords: COVID-19; UPSIT; anosmia; olfactory disorders; parosmia; prediction model; smell disorders; smell test.

Figure 1

Workflow chart of our study including 777 subjects suspected of being infected by COVID-19 from March to April 2020 in four different hospitals from the south of Spain. All patients completed a baseline questionnaire reporting the severity of their symptoms, including loss of smell and taste, measured through quantitative visual analog scales (VAS) during the acute phase of COVID-19 infection. To confirm the COVID-19 diagnosis, all patients were subjected to RT-PCR. Patients with a confirmed diagnosis of COVID-19 were recruited one year later to study the evolution of their symptoms, especially loss of smell and taste. A second questionnaire based on self-reported VAS and psychophysical evaluation of olfactory function through the UPSIT test were conducted in a group of volunteers with N = 102 and N = 64 subjects, respectively. Differences between the severity of smell and taste symptoms were compared at the baseline and at the 12 month-follow-up, and the correlation with psychophysical UPSIT scores was evaluated. The prevalence and clinical factors leading to other self-reported qualitative disorders such as parosmia were also analyzed in our study.

Figure 2

UPSIT scores at the 12-month follow up. (a) Boxplot distribution of UPSIT scores for different patient subgroups according to the severity of smell symptoms measured through VAS (No; mild; moderate, and severe) (b) Point distribution and correlation of UPSIT scores in relation to numeric VAS for loss of smell at the 12-month follow-up.