Smell and Taste Dysfunction After COVID-19 Persists in Some Patients

Among patients with COVID-19, some will experience long-term changes to their sense of smell or taste, and some may not regain function, according to a systematic review and meta-analysis published in The British Medical Journal.

Many patients with COVID-19 report changes to their taste and smell. It remains unclear how long these symptoms persist and whether there are specific risk factors for developing these symptoms.

Researchers at the National University of Singapore searched publication databases through October 2021 for studies of smell or taste dysfunction in COVID-19. A total of 18 studies were included in the individual patient data (IPD) meta-analysis and 68 articles in the systematic review and meta-analysis.

The IPD population comprised 3699 patients aged mean 30.0-55.8 years and 29.0%-79.4% were men. All but 1 study used self-report assessments to evaluate changes to taste and smell.

Smell was recovered by day 30 among 74.1% (95% CI, 64.0%-81.3%), day 60 among 85.8% (95% CI, 77.6%-90.9%), day 90 among 90.0% (95% CI, 83.3%-94.0%), and day 180 among 95.7% (95% CI, 89.5%-98.3%). The median recovery time was 14.9 (95% CI, 12.7-20.3) days.

In studies that quantified the degree of smell recovery, 12.8%-30.4% had partial recovery and 44.0%-70.0% full recovery. Persistent smell dysfunction may occur among 5.6% (95% CI, 2.7%-11.0%). The sensitivity analysis found similar results (6.6%).

Taste was recovered by day 30 among 78.8% (95% CI, 70.5%-84.7%), day 60 among 87.7% (95% CI, 82.0%-91.6%), day 90 among 90.3% (95% CI, 83.5%-94.3%), and day 180 among 98.0% (95% CI, 92.2%-95.5%). The median recovery time was 12.4 (95% CI, 10.3-16.3) days.

In studies that quantified the degree of taste recovery, 8.3%-30.0% had partial recovery and 50.0%-88.9% full recovery. Persistent taste dysfunction may occur among 4.4% (95% CI, 1.2%-14.6%). The sensitivity analysis predicted more were at risk for persistent dysfunction (8.2%).

The aggregate systematic review evaluated 20 symptoms, 16 medical interventions or treatments, 11 personal characteristics, 11 past medical conditions, 11 biochemical variables, 7 characteristics of COVID-19, and 4 characteristics of smell or taste dysfunction.

Women were less likely to recover smell (odds ratio [OR], 0.52; 95% CI, 0.37-0.72; I², 20%) or taste (OR, 0.31; 95% CI, 0.13-0.72; I², 78%). Smell recovery was less likely among those with greater smell dysfunction (OR, 0.48; 95% CI, 0.31-0.73; I², 10%) and nasal congestion (OR, 0.42; 95% CI, 0.18-0.97; I², 0%).

The major limitation of this analysis was that most underlying studies relied on self-reported symptomology.

This study found that approximately 5% of patients were likely to experience long-term dysfunction of smell or taste.

“Women were less likely to recover their sense of smell and taste. Patients with higher initial severity of dysfunction and patients with nasal congestion were also less likely to recover their sense of smell,” the researchers stated.