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Sudden impaired sense of smell may be the most significant symptom of early COVID-19 infection

Sudden impaired sense of smell may be the most significant symptom of early COVID-19 infection


The British government has just issued a warning: "From today, all individuals should continue to isolate themselves if they continue to cough, have a fever or lose their sense of smell."

Sudden loss of smell is an important indicator, because it may be the early symptom of COVID-19 infection, and sometimes even the only symptom.

The earliest clues linking loss of smell to COVID-19 infection appeared in early March 2020, and otolaryngologists on Facebook noticed a large number of new olfactory disorders. What followed was gradually accumulating evidence linking loss of smell to COVID-19.

The number of people searching Google for "anosmia" has increased, and high-profile cases have been reported in the news. This included a neurosurgeon with no other symptoms. Two days later, his COVID-19 test was positive.

Loss of smell is a new discovery that can distinguish COVID-19 from the common cold or flu. ENT-UK and the British Rhinology Association issued an early statement calling for the loss of sense of smell to be a hallmark of the virus.

However, although the cases and anecdotes are convincing, they lack large datasets for scientific research.

The first large data set is from Iran. A family study of 10,000 people showed a correlation between loss of smell and COVID-19. The results of the second large data set were published by the team at King ’s College London.

Their COVID symptom research application shows that this symptom is by far the best predictor of COVID-19. Preliminary results from the first survey of the Global Chemical Sensing Research Consortium (GCCR) show that people reporting COVID-19 symptoms have an average 80% reduction in olfactory ability.

These investigations increase the weight of anecdotal evidence, but have their limitations. The main reason is that they are based on people ’s self-reports—that is, their olfactory ability has not been clinically evaluated.

On the other hand, studies based on hospitals and otolaryngology clinics provide valuable evidence to clarify the status and medical history of COVID-19 infected persons with greater certainty.

The earliest report appeared in China, and researchers pointed out that 5% of patients in China have impaired sense of smell.

Studies conducted in France (417 patients), Italy (202), and the United States (102) found that 86%, 64%, and 68% of all COVID-19 positive patients had decreased olfactory sensitivity, respectively.

The study that best illustrates the problem comes from Iran, who measured the olfactory ability of the subjects using a recognized scratch and olfactory test.

In this case, 59 of 60 COVID-19 patients had a decreased sense of smell. After evaluating the latest three pieces of evidence, it is concluded that there is a strong correlation between COVID-19 and loss of smell.

Early warning signal

A US study found that in 27% of the reactions, smell is the first symptom.

A team from China has shown that even if you only have symptoms of a sense of smell, you can still be contagious.

Of course, we also need a rigorous evidence-based approach, including objective odor testing and evidence of the mechanisms involved, some of which are emerging. At the same time, it is recommended that everyone regard the sudden loss of smell as a sign that we should isolate ourselves.

If you experience a sudden loss of smell or taste during a pandemic, you can log in and fill out the UK and Global GCCR questionnaire . These simple online questionnaires take less than ten minutes. Our focus is on understanding the mechanisms associated with odor and taste disorders.

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