Sudden loss of smell and taste are symptoms of SARS-CoV-2 infection, the respiratory illness caused by the newly identified coronavirus.
Experts suggest that sensory loss tends to be seen in patients with mild to moderate infections, indicating that the rate of recovery is high.
Loss of smell and taste could also help health services to quickly verify which patients should be admitted to hospital for treatment.
Dr Carol Yan, the study’s first author, said:
“Based on our study, if you have smell and taste loss, you are more than 10 times more likely to have COVID-19 infection than other causes of infection.
The most common first sign of a COVID-19 infection remains fever, but fatigue and loss of smell and taste follow as other very common initial symptoms.
We know COVID-19 is an extremely contagious virus.
This study supports the need to be aware of smell and taste loss as early signs of COVID-19.”
The loss of smell and taste is not mild but complete, but patients’ sensory function returns to normal in less than four weeks from infection.
Yan and colleagues in their previous study showed that fever, fatigue, and loss of sensory function are common early symptoms of COVID-19 disease.
Dr Yan in his latest study said:
“Normosmia or the normal sense of smell is an independent predictor of admission in COVID-19 cases.
In previous research, we found that loss of olfactory function is a common early symptom, following fever and fatigue.
What’s notable in the new findings is that it appears that loss of smell may be a predictor that a SARS-CoV-2 infection will not be as severe, and less likely to require hospitalization.
If an infected person loses that sense, it seems more likely they will experience milder symptoms, barring other underlying risk factors.”
These risk factors are age, since the severity of the illness is much higher in older people, cardiovascular disease, lung disease, obesity, and diabetes.
The study found that hospitalised COVID-19 patients were less likely to lose their sense of taste, which is known as dysgeusia, or loss of smell, which is called anosmia.
About 27 percent of these patients reported dysgeusia or anosmia symptoms, whereas 67 percent of patients with mild to moderate COVID-19 infection exhibiting these two signs.
Dr Adam S. DeConde, study co-author, said:
“Patients who reported loss of smell were 10 times less likely to be admitted for COVID-19 compared to those without loss of smell.
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.”
It appears that if the virus settles in the upper airway and nose at the start then it will impact olfactory function.
This in turn could lead to less severe and sudden symptoms of the illness and so reduce the response of the immune system and the chance of lung failure.
Dr DeConde said:
“The site and dosage of the initial viral burden, along with the effectiveness of the host immune response, are all potentially important variables in determining the spread of the virus within a person and, ultimately, the clinical course of the infection.
This is a hypothesis, but it’s also similar to the concept underlying live vaccinations.
At low dosage and at a distant site of inoculation, the host can generate an immune response without severe infection.”
Loss of smell could be a clue to a localised strong immune response in the nasal passages causing the body’s defence system to activate less in other parts of the body.
The study was published in International Forum of Allergy & Rhinology (Yan et al., 2020).