Olfactory and taste disorders appear to be a common feature of COVID-19 disease, clinicians in Europe and China say.
After hearing anecdotal reports of patients with COVID-19 describing symptoms such as metallic taste in the early stages of the disease, doctors at the III Infectious Diseases Unit, ASST-FBF-Sacco, Milan, interviewed 59 with acute infection in relation to loss of taste or smell.
They found that 20 (33.9%) reported at least one taste or olfactory disorder and 11 (18.6%) both.
Taste alterations were more frequently (91%) reported before hospitalisation, whereas both taste and olfactory alteration appeared with equal frequency after hospitalisation.
Patients with olfactory and taste disorders were more likely to be females than males (53% vs 25%) and younger than people without.
The report authors said olfactory and taste disorders were known to be associated with a wide range of viral infections, possibly due to viral transneural penetration through the olfactory bulb.
One possible mechanism might involve the ACE2 receptor by which the SARS-CoV-2 binds and penetrate into the cell, and which is widely expressed on the epithelial cells of the mucosa of oral cavity.
The high frequency of olfactory and taste disorders in patients with COVID-19 infection, especially before the onset of full-blown clinical disease, may prove to be useful in screening high risk patients, they suggested in Clinical Infectious Diseases.
Loss of smell as a possible marker of asymptomatic COVID-19 infection has also been highlighted by ENT specialists in the UK.
They noted that post-viral anosmia was one of the leading causes of loss of sense of smell in adults, accounting for up to 40% of cases.
“Previously described coronaviruses are thought to account for 10- 15% cases. It is therefore perhaps no surprise that the novel COVID-19 virus would also cause anosmia in infected patients,” said the surgeons in a statement released by the ENT UK network.
“In Germany it is reported that more than 2 in 3 confirmed cases have anosmia. In South Korea, where testing has been more widespread, 30% of patients testing positive have had anosmia as their major presenting symptom in otherwise mild cases,” they wrote.
“I have personally seen four patients this week, all under 40, and otherwise asymptomatic except for the recent onset of anosmia – I usually see roughly no more than one a month,” said Prof Claire Hopkins, Consultant ENT Surgeon, Guy’s and St Thomas’ Hospitals and President of the British Rhinological Society.
“I think these patients may be some of the hitherto hidden carriers that have facilitated the rapid spread of COVID-19. Unfortunately, these patients do not meet current criteria for testing or self isolation.”