In a new study, researchers found how smell loss linked to COVID-19 infection differs from what you typically might experience with a bad cold or flu.
The main differences are that, although COVID-19 patients also lose their sense of smell, they can breathe freely, do not tend to have a runny or blocked nose, and they cannot detect bitter or sweet tastes.
These findings lend weight to the theory that COVID-19 infects the brain and central nervous system.
The study is the first to compare how people with COVID-19 smell and taste disorders differ from those with other causes of upper respiratory tract infections.
The researchers hope that their work could help develop smell and taste tests for fast COVID-19 screening—in primary care and emergency departments.
The research was conducted by a team at the University of East Anglia and elsewhere.
The loss of smell and taste is a prominent symptom of COVID-19, however, it is also a common symptom of having a bad cold.
In the study, the team wanted to find out exactly what differentiates COVID-19 smell loss with the kind of smell loss people might have with a cold and blocked-up nose.
The researchers 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 for age and sex.
They wanted to see if their smell and taste test scores could help discriminate between COVID-19 patients and those with a heavy cold.
Previous research has shown that COVID-19 behaves differently to other respiratory viruses, for example by causing the body’s immune system to over-react, known as a cytokine storm, and by affecting the nervous system.
The team suspected that patterns of smell loss would differ between the two groups.
They found that smell loss was much more profound in the COVID-19 patents. They were less able to identify smells, and they were not able to identify bitter or sweet tastes.
In fact, it was this loss of true taste that seemed to be present in the COVID-19 patients compared to those with a cold.
This means that smell and taste tests could be used to discriminate between COVID-19 patients and people with a regular cold or flu.
The team says although such tests could not 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.
One author of the study is Prof Carl Philpott from UEA’s Norwich Medical School.
The study is published in Rhinology.
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