Persistent Post-COVID-19 Olfactory Dysfunction and Its Association with Autonomic Nervous System Function: A Case-Control Study

Abstract

Background: Following the Coronavirus Disease 2019 (COVID-19) pandemic, many patients have reported ongoing smell and taste issues. This study aims to investigate the prevalence of olfactory and gustatory dysfunction among patients with a history of COVID-19 and its association with autonomic dysfunction and disability.

Patient and methods: This case-control study included a COVID-19 group (n = 82) and a control group (n = 82). Olfactory dysfunction, including parosmia and taste problems, was explored using self-reports and the Quick Smell Identification Test (QSIT). The association between post-COVID-19 disability severity and taste and smell alterations was also analyzed. Moreover, autonomic function was evaluated using the Composite Autonomic Symptom Scale-31 (COMPASS-31) to assess the association between autonomic and olfactory dysfunction.

Results: Significantly higher rates of ongoing smell (26.8%) and taste (14.6%) dysfunction were reported for the post-COVID-19 group compared to the control group. Post-COVID-19 patients reported 36.6 times more smell issues and 8.22 times more taste issues than controls. Parosmia scores were significantly worse in the post-COVID-19 group, while QSIT scores showed no significant difference between the groups. However, those with worse QSIT scores exhibited significantly more ongoing smell issues. No significant association was observed between disability and altered smell or taste. Higher secretomotor dysfunction scores were significantly associated with abnormal QSIT scores and worse parosmia scores; the other domains of the COMPASS-31 scale showed no significant associations.

Conclusions: The findings indicated a potential link between autonomic and olfactory dysfunction. Further studies are needed to elucidate the mechanisms underlying persistent olfactory and autonomic dysfunction in post-COVID-19 patients.

Keywords: autonomic dysfunction; post-COVID-19; subjective and objective smell tests.

Figure 1

Significant influences on the prevalence of ongoing smell and taste issues and parosmia. Predictors of olfactory dysfunction in post-COVID-19 patients (n = 82) and control group (n = 82). Associations are shown between ongoing smell issues with group (a) and QSIT score (b), between ongoing taste issues with group (c) and age in years (d), and between parosmia with group (e). Parosmia Score equation: (Total Score − 4)/12) × 100. Error bars and shaded areas represent the 95% confidence interval around model estimates.. QSIT = Quick Smell Identification Test.

Figure 2

Association between higher secretomotor symptom scores as per Composite Autonomic Symptom Scale 31 (COMPASS-31) questionnaire item totals with more likely abnormal QSIT (scores of 2 or lower) (a) scores and worse parosmia scores (b). Logistic (abnormal QSIT score) and linear (parosmia score) regression model estimates were derived while adjusting for participant age, smoking status (past or present smoker vs. never), and duration since COVID-19 infection. Shaded areas represent the 95% confidence interval around model estimates. QSIT = Quick Smell Identification Test.

Figure 3

Association between post-COVID-19 disability groups (measured using the WHO Disability Assessment Schedule) and the presence of smell issues following acute illness (a), ongoing post-COVID-19 smell issues (b), taste issues following acute illness (c), and ongoing post-COVID-19 taste issues (d). Estimates show predicted probability as calculated using logistic regression modeling, with error bars depicting the 95% confidence interval around model estimates. The post-COVID disability group was not significantly associated with any of the four outcomes. Total simple scoring system of WHODAS scores categorize disability levels: none (0 points), mild (1–4 points), moderate (5–9 points), or severe (10–14 points).