Taste Dysfunction May Linger After COVID-19

Taste dysfunction may linger after acute COVID-19 infection and may not necessarily be a consequence of olfactory dysfunction, a cross-sectional study in Italy showed.

In a group of people who reported losing their sense of taste for months after they had COVID, 42% were found to have true hypogeusia, reported Paolo Boscolo-Rizzo, MD, of the University of Trieste in Italy, and co-authors.

Most people with post-COVID hypogeusia also had olfactory impairment, but about 3% did not, the researchers wrote in JAMA Otolaryngology-Head & Neck Surgery.

“The classical thinking is that loss of taste in most cases directly results from a loss of smell,” Joshua Levy, MD, MPH, of Emory University School of Medicine in Atlanta, who wasn’t involved with the study, told MedPage Today.

“What we’re seeing unique to COVID is that there can be a direct impact on taste that’s separate from the loss of smell,” he continued. “It looks like the ACE receptors, which are the viral points of entry, are not only located adjacent to the olfactory nerves but may even be related to some of the taste receptors, so there can be a direct insult to taste without a disruption in smell.”

Temporary loss of smell and taste often occurs after SARS-CoV-2 infection, with some patients reporting dysfunction long after the acute phase of the disease. Self-reported olfactory function and psychophysical tests have shown poor agreement in past studies, but gustatory function has not been studied as extensively, Boscolo-Rizzo and colleagues noted.

The researchers evaluated 105 patients with self-reported altered sense of taste that lasted more than 3 months after acute SARS-CoV-2 infection. Almost all (94%) self-reported an associated olfactory impairment.

Patients had a median age of 45, and 76% were women. Nearly all (98%) had mildly symptomatic COVID-19 with no evidence of pneumonia.

Psychophysical evaluations were performed a median of 226 days after illness onset. Orthonasal olfactory function was measured using the extended Sniffin’ Sticks test battery; gustatory evaluation was performed using the Taste Strips test; and retronasal olfactory function was tested using 20 powdered tasteless aromas.

For orthonasal function, Threshold, Discrimination, and Identification (TDI) scores indicated normosmia (TDI ≥30.75), hyposmia (TDI 16.25-30.5), or anosmia (TDI ≤16.0). For taste, Taste Strips Score (TSS) identified hypogeusia (TSS <9 points) and normogeusia (TSS ≥9 points).

Based on TSS, the prevalence of hypogeusia was 41.9%, which dropped to 28.6% when scores were related to participants’ age. Only three out of 105 patients (2.9%) had hypogeusia and were normosmic at psychophysical evaluation.

Among the 61 patients who were normogeusic, 83.6% had a TDI score less than 30.75, and 26.2% had a retronasal score less than 12. Only 16.4% had both normal orthonasal and retronasal olfactory function.

Olfactory training may help patients whose problems stem from smell loss, but additional strategies may be needed for patients with lingering gustatory impairment, Boscolo-Rizzo and co-authors noted.

“An awareness that we need to expand our treatment from beyond just smell is very important,” Levy said. “That would mean we look for other causes like vitamin deficiencies, things that don’t really relate to someone who had COVID.”

There’s a need for therapies to address taste dysfunction, Levy added. “We don’t have good options to address this smaller group of patients with disrupted taste, but intact smell,” he said.

The study had several limitations, Boscolo-Rizzo and colleagues noted. It lacked an age-matched control group and evaluated different patients at different time points. Using a single sensory technique to characterize taste function may have produced false-negative results, and dysgeusia, phantogeusia, parosmia, and phantosmia were not addressed in the study.

In addition, most participants had mildly symptomatic COVID-19 and the sample mainly consisted of women; results may not apply to others.