Unmasking Risk Factors for Post-COVID-19 Olfactory Dysfunction Resulting From Early Stages of the Pandemic: A Case-Control Study of Lost and Lingering Smells.

Introduction: The COVID-19 pandemic has highlighted olfactory dysfunction (OD) as a major and often persistent symptom in affected individuals. Thus, it is important to identify demographic and clinical factors contributing to OD among patients with COVID-19.

Methods: A case-control (1:3) study was performed in adult patients with COVID-19 diagnosis between July 2020 and June 2021. Cases had OD; controls did not have OD. OD was subclassified as acute smell loss (< 3 months), chronic smell loss (> 3 months), or altered sense of smell (eg, parosmia, phantosmia). Bivariate tests and multivariable logistic regression were performed for analysis.

Results: Of the 4220 patients that met criteria, 1055 (25%) had OD. Of those with OD, 650 (61.6%) had acute smell reduction, 350 (33.2%) had chronic smell reduction, and 245 (23.2%) had altered sense of smell. Older (odds ratio [OR], 0.84; 95% confidence interval [CI], 0.79-0.89), male (OR, 0.62; 95% CI, 0.54-0.72), and Asian (OR 0.75; 95% CI, 0.59-0.95) patients were less likely to experience OD. Having seasonal allergies (OR, 1.44; 95% CI, 1.11-1.86) and being hospitalized (OR, 1.52; 95% CI, 1.14-2.02) increased the likelihood of OD development. Compared with acute loss, chronic smell loss was likelier in older, female, non-White, hospitalized, and cerebrovascular disease patients (P < .05).

Discussion: Understanding the course of post-COVID-19 OD is becoming increasingly important and may broaden these insights.

Conclusion: Being younger, female, and atopic conferred highest likelihood of OD development after COVID-19.