A timeline of recovery for post-COVID-19 olfactory dysfunction based on psychophysical performance: a scoping review and meta-analysis

Quantifying the prevalence of persistent COVID-19-associated olfactory dysfunction (C19OD) and estimating the timeframe for recovery of a functional sense of smell remains challenging. While self-reported recovery has notable limitations, psychophysical olfactory assessment provides a validated and standardized measure of olfactory status. To better understand C19OD prevalence, we conducted a meta-analysis using psychophysical olfactory data from studies of adults with previously confirmed SARS-CoV-2 infection.

Our primary aim was to estimate the percentage of individuals who eventually recovered their sense of smell, defined as normosmia on psychophysical testing after at least 3 months of C19OD. Initial screening identified 583 abstracts, after which we conducted a full-text review of 151 studies, of which 64 comprising 9981 participants met the inclusion criteria. Estimates of recovery varied substantially by study design.

Meta-regression analyses revealed that only longitudinal studies demonstrated a significant recovery trajectory over time, with predicted normosmia prevalence increasing from 46.0% at 3 months to 76.7% at 24 months post-infection. Cross-sectional meta-regression showed no significant association between time and normosmia prevalence in either recruitment frame. General post-COVID populations had greater prevalence of normosmia at 12–24 months (61.1%) than those with self-reported OD or long-COVID (30.2%), highlighting the disproportionate burden of persistent C19OD in these groups.

The prevalence of C19OD is higher in studies using psychophysical testing than in earlier estimates based on self-report, which tends to underestimate deficits. The authors thank Michelle Demetres for her assistance in curating search terms for the scoping review. This project was supported by the NIDCD of the National Institutes of Health under grant K23DC019678.

This publication was supported by the National Center for Advancing Translational Sciences, National Institutes of Health, through Grant Number UL1TR001873. Department of Otolaryngology-Head and Neck Surgery, NewYork-Presbyterian/Columbia University Irving Medical Center, 180 Fort Washington Avenue, HP8, New York, NY, 10032, USA Jeremy P. Overdevest Department of Otolaryngology-Head and Neck Surgery, University of California San Francisco, 505 Parnassus Ave, San Francisco, CA, 94143, USA Department of Otolaryngology-Head and Neck Surgery, Yale School of Medicine, 330 Cedar Street PO 208041, New Haven, CT, 06520, USA Columbia University Irving Medical Center, New York Presbyterian, 180 Fort Washington Avenue, HP8-873, New York, NY, 10032, USA Correspondence to Jonathan B.

The authors declare no competing interests. Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Below is the link to the electronic supplementary material. ((“Smell”[MeSH] OR “olfaction disorders”[MeSH] OR “Anosmia”[MeSH] OR smell[tiab] OR olfact*[tiab] OR phantosmia*[tiab] OR parosmia*[tiab] OR hyposmi*[tiab] OR anosmi*[tiab] OR cacosmi*[tiab] OR dysosmi*[tiab]) AND (“COVID-19”[MeSH] OR “SARS-CoV-2”[MeSH] OR “Post-Acute COVID-19 Syndrome”[MeSH] OR COVID[tiab] OR “SARS-CoV-2”[tiab] OR nCoV[tiab]) AND (psychophysical[tiab] OR Sniff*[tiab] OR “Smell identification test“[tiab] OR threshold[tiab] OR discrimination[tiab])) (smelling/or smelling disorder/or anosmia/or (smell or olfact* or phantosmia* or parosmia* or hyposmi* or anosmi* or cacosmi* or dysosmi*).tw.) and (coronavirus disease 2019/or long COVID/or (COVID or “SARS-CoV-2” or nCoV).tw.) and (psychophysical or sniff* or smell identification test or threshold or discrimination).tw.