- Sudden loss of smell is now an official symptom of Covid-19
- Loss of smell is also common during other respiratory illnesses, but differs from Covid-19
- The differences could be important to help distinguish between Covid-19 and other illnesses
As research on Covid-19 progressed, loss of smell (anosmia) as a symptom was officially added to the Centers for Diseases Control and Prevention’s list of Covid-19 symptoms. At that stage, it still wasn’t clear what caused this phenomenon.
A previous Health24 article explored the possibility that loss of smell could be a neurological indicator of early infection with the new coronavirus.
Now, new research shows that the smell disorder in Covid-19 differs from similar symptoms caused by other forms of upper respiratory tract infections.
The difference between Covid-19 and the common cold
According to the researchers, whose study was published in the journal Rhinology, the main difference between loss of smell caused by Covid-19 and that of a cold is the way people breathe. People who lose their sense of smell as a result of Covid-19 are still able to breathe freely through their noses, but are unable to detect bitter or sweet tastes.
Loss of smell as a result of other infections such as a common cold is accompanied by a runny or blocked nose.
The research team carried out smell and taste tests on 10 Covid-19 patients, 10 people with bad colds and a control group of 10 healthy people – all matched according to age and sex.
"We wanted to see if their smell and taste test scores could help discriminate between Covid-19 patients and those with a heavy cold. We know that Covid-19 behaves differently to other respiratory viruses, for example by causing the body's immune system to overreact, known as a cytokine storm, and by affecting the nervous system,” remarked Professor Carl Philpott from the University of East Anglia's Norwich Medical School and lead author of the study.
Covid-19 smell loss linked to central nervous system
While smell loss from a common cold is caused by the direct blockage of the nasal passages, the smell loss from Covid-19 can be linked to the central nervous system.
"It has previously been suggested that the Covid-19 virus affects the central nervous system, based on the neurological signs developed by some patients. There are also similarities with SARS, which has also been reported to enter the brain, possibly via smell receptors in the nose. Our results reflect, at least to some extent, a specific involvement at the level of the central nervous system in some Covid-19 patients,” said Prof Philpott.
This finding could make the diagnosis of Covid-19 easier. Although such tests cannot replace formal diagnostic tools such as throat swabs, they could provide an alternative when conventional tests are not available or when rapid screening is needed – particularly at the level of primary care, in emergency departments or at airports.
"This research also shows that there are altogether different things going on when it comes to smell and taste loss in Covid-10 patients, compared to those with a bad cold,” Prof Philpott stated in the news release.
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