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Reduced sense of smell important marker for COVID-19

Loss of smell is the single most important symptom of COVID-19. Individuals who rate their sense of smell to 0-2 on a scale of 0-10 have a high probability of being infected by the coronavirus, according to a new large international study.

Changes in sense of smell and taste is the single most important symptom of COVID-19. This is shown by previous studies and confirmed by a new study published in the scientific journal Chemical Senses. Also, the new research shows that using a simple method with a scale 0-10, where zero is complete loss of smell and ten is normal, makes loss of smell even more precise as a symptom of the infection. Someone who rates their sense of smell to zero are ten times more likely to have COVID-19 than those with normal sense of smell.

Jonas Olofsson. Foto: Henric Bergqvist
Jonas Olofsson. Photo: Henric Bergqvist

“Other respiratory infections often cause a minor decrease in the sense of smell, but a very large change is a particular phenomenon for COVID-19. With 83 percent certainty, other causes can be ruled out for those who estimate their sense of smell to 0-2 on a scale of 0-10,” says Jonas Olofsson, professor at the Department of Psychology, Stockholm University, specialized in the sense of smell.
“This means that our study where participants rate loss of smell has better precision than other studies where participants only answer yes or no.”

The study is based on a large international survey, 15,747 people were included in the analysis, and is part of a large collaboration between over 500 researchers.

“Changes in the sense of smell should be taken seriously as one of the main symptoms of COVID-19. It has sometimes been described as a less common symptom, but it is actually the most common. If doctors use this scale and the patient rate how the sense of smell has changed, it can be a contribution to making the diagnosis,” says Jonas Olofsson.

Does that mean you probably do not have COVID-19 if your sense of smell is normal? No, affected sense of smell is admittedly the most common symptom, but only one of several. Other studies show that about half of those who get the disease have a normal sense of smell. A normal sense of smell does not mean that covid-19 can be ruled out, but a lost sense of smell increases the probability of being infected.

“An almost completely lost sense of smell is a strong indication, and then you should isolate yourself,” says Jonas Olofsson.

The researchers will now follow up on the people in the survey to see how their sense of smell has recovered. Together with Johan Lundström at Karolinska Institutet, also co-author of the study, Jonas Olofsson will investigate different ways of training the sense of smell with the aim of recovery. Read more at www.lukttraning.se (in Swedish)

“Many affected persons describe both lost and distorted sense of smell. Suddenly the food tastes bad and the partner smells bad. These are very difficult changes to handle,” says Jonas Olofsson.

The article “The best COVID-19 predictor is recent smell loss: a cross-sectional study” is published in the scientific journal Chemical Senses.