An Explanation for Reports of Increased Prevalence of Olfactory Dysfunction With Omicron: Asymptomatic Infections

Area of Science:

• Infectious Diseases
• Neurology
• Epidemiology

Background:

• Olfactory dysfunction (OD) is a known symptom of coronavirus disease 2019 (COVID-19).
• The Omicron variant of SARS-CoV-2 has been associated with a lower incidence of OD compared to previous variants.
• Recent studies have reported conflicting findings regarding OD prevalence in Omicron infections.

Purpose of the Study:

• To investigate the discrepancy in reported olfactory dysfunction (OD) prevalence associated with the Omicron variant.
• To identify potential methodological flaws in studies reporting a high prevalence of OD with Omicron infections.
• To propose a method for accurately estimating OD prevalence in the context of widespread asymptomatic SARS-CoV-2 infections.

Main Methods:

• Analysis of existing literature on olfactory dysfunction (OD) prevalence in Omicron variant infections.
• Identification and critique of methodological biases in outlier studies.
• Theoretical modeling of OD prevalence estimation based on cohort representativeness and asymptomatic infection rates.

Main Results:

• Studies reporting a significantly increased prevalence of OD with Omicron are likely based on non-representative cohorts.
• A major methodological flaw involves examining predominantly symptomatic subjects, excluding asymptomatic cases.
• This bias can artificially inflate the estimated prevalence of OD by up to 10-fold.

Conclusions:

• The substantially reduced prevalence of olfactory dysfunction (OD) with the Omicron variant is likely accurate.
• Outlier studies overestimating OD prevalence suffer from significant selection bias.
• Accurate estimation of OD prevalence necessitates the inclusion of asymptomatic cases in study cohorts.