Olfactory and taste dysfunctions in COVID-19

Area of Science:

• Neurology
• Infectious Diseases
• Otorhinolaryngology

Background:

• Olfactory dysfunction (OD) is a prominent early symptom of COVID-19, distinguishing it from MERS and SARS.
• Existing OD data are often non-peer-reviewed, inconclusive, and present contradictory findings due to incongruent subjective and objective testing.
• Mechanisms underlying OD and taste dysfunction (TD) in COVID-19 are still being elucidated, often relying on models from previous SARS and MERS outbreaks.

Purpose of the Study:

• To review and analyze current literature on OD and TD during the COVID-19 pandemic.
• To examine the pathogenesis, clinical correlates (prevalence, recovery, risk factors), and predictive value of OD.
• To evaluate subjective and objective olfactory testing methods and discuss management challenges for patients with OD and rhinitis.

Main Methods:

• Comprehensive literature review of studies on OD and TD in COVID-19 patients.
• Analysis of data on prevalence, recovery rates, risk factors, and predictive power of OD.
• Evaluation of various subjective and objective olfactory testing methodologies.

Main Results:

• Subjective smell testing likely underestimates the true prevalence, severity, and recovery rates of OD compared to objective measures.
• OD is a predictor of COVID-19 infection, especially when accompanied by TD.
• Current data suggest neurotropism of SARS-CoV-2 for the olfactory neuro-epithelium and a potential role for transient receptor potential (TRP) channels.

Conclusions:

• Recognizing the limitations of both subjective and objective chemosensory testing is vital for managing OD and TD in COVID-19 patients.
• Further research into the neurogenic inflammation associated with COVID-19 is warranted.
• Neurotropism and TRP channel involvement are potential mechanistic pathways for COVID-19-related OD.