Loss of smell is more likely to occur in patients with mild to moderate Covid-19 than in those with more severe illness, a new study finds.
This information could give health care providers an early indication of which patients may require hospitalisation, according to the University of California, San Diego Health researchers.
"One of the immediate challenges for health care providers is to determine how to best treat persons infected by the novel coronavirus," said study first author Dr Carol Yan, a rhinologist and head and neck surgeon.
"If they display no or mild symptoms, can they return home to self-quarantine or will they likely require hospitalisation? These are crucial questions for hospitals trying to efficiently and effectively allocate finite medical resources," she said in a university news release.
An independent factor
In previous research, Yan and her colleagues found that loss of smell is a common early symptom, following fever and fatigue.
The new study included 169 patients who tested positive for Covid-19 at UC San Diego Health. Data on taste and smell were obtained for 128 of the patients, 26 of whom were hospitalised.
Hospitalised patients were much less likely to experience loss of smell (anosmia) than those who weren't hospitalised, about 27% vs. 67%, and similar rates were seen for loss of taste.
"Patients who reported loss of smell were 10 times less likely to be admitted for Covid-19 compared to those without loss of smell," said study senior author Dr Adam DeConde, a rhinologist and head and neck surgeon.
"Moreover, anosmia was not associated with any other measures typically related to the decision to admit, suggesting that it's truly an independent factor and may serve as a marker for milder manifestations of Covid-19," DeConde said in the release.
The study was published online in the journal International Forum of Allergy & Rhinology.
Strong immune response
"What's notable in the new findings is that it appears that loss of smell may be a predictor that a SARS-CoV-2 (the scientific name for the new coronavirus) infection will not be as severe, and less likely to require hospitalisation. If an infected person loses that sense, it seems more likely they will experience milder symptoms, barring other underlying risk factors," Yan said.
The findings suggest that if the coronavirus first concentrates in the nose and upper airway, the immune system has an opportunity to attack the virus there and prevent more serious illness that affects other areas of the body, according to the researchers.
They said loss of smell might be an indication of a strong immune response against the coronavirus.
"This is a hypothesis, but it's also similar to the concept underlying live vaccinations," DeConde said. "At low dosage and at a distant site of inoculation, the host can generate an immune response without severe infection."