COVID-19 Associated Loss of Smell, Taste Mostly Resolves Within Weeks

By Linda Carroll

July 06, 2020

(Reuters Health) - Most adults with a mild form of COVID-19 who have lost their ability to taste or smell as an early disease symptom will get those senses back, at least in part, a new study suggests.

In a survey of more than 100 adults with mild COVID-19 who suddenly lost their sense of smell or taste, nearly 90% either experienced complete resolution or some improvement of those symptoms within four weeks of onset, according to the results published in JAMA Otolaryngology-Head & Neck Surgery.

Gender and age appeared to have little influence on the likelihood of smell and taste recovery but symptom severity did, the researchers, led by Dr. Paolo Boscolo-Rizzo, of the University of Padova in Treviso, Italy, report.

"A higher severity of smell and taste impairment at baseline, reasonably due to a more severe injury to the olfactory neuroepithelium, was associated with a lower likelihood of recovery at four weeks," the researchers write.

"The pathogenesis of olfactory dysfunction in COVID-19 may be secondary to mucosal obstruction of the olfactory cleft, leading to a conductive loss, or may reflect a direct effect on olfactory mucosa and the olfactory sensory neurons with consequently a sensorineural loss," the researchers add. "This latter mechanism seems to be supported by our observation that most patients did not report nasal obstruction, and in those who did, the recovery of altered sense of smell or taste was independent from improvement in blocked nose."

Of the 187 patients with mild COVID-19 who responded to a survey that included a question about loss of taste and smell at the beginning of the study, 113 reported smell or taste impairment. Another 11 patients reported subsequent loss of those senses, resulting in a prevalence of 66%.

When Boscolo-Rizzo and his colleagues followed up four weeks later with the 113 patients who reported sudden onset of those symptoms in the two weeks prior to testing for SARS-CoV-2, they found that 48.7% had complete resolution of their smell or taste impairment, while another 40.7% experienced a decrease in the severity of the symptom. Just 10.6% said there was no improvement.

What's new in this study is the information on recovery, said Dr. Nicholas Rowan, an assistant professor in the department of otolaryngology-head and neck surgery at the Johns Hopkins School of Medicine in Baltimore.

"Multiple systematic reviews indicated that the overall prevalence of smell or taste dysfunction in the setting of COVID-19 is around 50%-60%, however, the limited studies with more objective data demonstrate a significantly higher prevalence of OD," Dr. Rowan said. "For instance, a recent report from Iran demonstrated an objective olfactory deficit in 98% of all patients hospitalized with COVID-19 and a staggering 91% of patients with complete anosmia or severe microsmia, though their patient population was notably different from these patients with mild infection."

The new study should prompt physicians to follow up with patients who report sensory loss, Rowan said.

"While the complete improvement of (about) 50% of patients is reassuring that many patients will experience full recovery, the 10% that did not experience at least an improvement, suggests that we should remain vigilant as a medical community on this important symptom," Dr. Rowan said in an email. "Rigorous smell testing is imperative."

Loss of the senses of taste and smell is not uncommon with a viral infection, Dr. Rowan said. "The presentation of smell loss in COVID-19 is unique in that typically other nasal and sinus symptoms - nasal blockage, stuffiness, congestion, facial pain/pressure - are missing," he added.

The new study, like some earlier reports, has an important limitation, Dr. Rowan said. "Many of these publications, as does this current publication, include subjective data," he explained. "Though the mounting body of evidence is undeniable, these subjective reports unfortunately do have limits, as self-reported tests/data generally significantly underestimate (what is found with) more sensitive and objective tests. This study in particular is further limited by asking a single question, on a scale of 0-5, of how poor the patient's sense of smell/taste is."

SOURCE: https://bit.ly/2C3AM0A and https://bit.ly/2ZvXAxN JAMA, online July 2, 2020. (Editing by Christine Soares)

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