Scientists have discovered that a loss of smell or taste could now be one of the most reliable warnings of whether a person has been infected with coronavirus. 

It comes as new research has suggested that four out of five people experiencing this have tested positive for Covid-19 antibodies.

The findings suggest an acute loss of smell or taste is a highly reliable virus indicator, scientists say.

They add that loss of smell or taste should now be considered globally as a criterion for self-isolation, testing and contact tracing.

Researchers at UCL and UCLH (University College London Hospitals NHS Foundation Trust) assessed health data from primary care centres in London.

They found that 78 per cent of people who reported sudden loss of smell and/or taste at the height of the pandemic had Covid-19 antibodies.

Of these people, 40 per cent did not have a cough or fever.

Although the symptom is already widely known, according to the researchers it is the first time such a figure has been calculated.

Lead author Professor Rachel Batterham, of UCL Medicine and UCLH, said: “As we approach a second wave of infections, early recognition of Covid-19 symptoms by the public together with rapid self-isolation and testing will be of vital importance to limit the disease’s spread.

“While people in the UK who experience sudden onset loss of smell or taste are advised to self-isolate and seek a test, at a global level few countries recognise this symptom as a Covid-19 indicator – most focus on fever and respiratory symptoms.

“Our findings show that loss of smell and taste is a highly reliable indicator that someone is likely to have Covid-19 and if we are to reduce the spread of this pandemic, it should now be considered by governments globally as a criterion for self-isolation, testing, and contact tracing.”

Between April 23 and May 14, researchers sent texts to people registered with a number of primary care centres in London who had reported sudden loss in their sense of smell and/or taste.

A total of 590 participants enrolled via a web-based platform and responded to questions about loss of smell and taste and other Covid-19–related symptoms.

Of these, 567 then had a consultation with a healthcare professional who confirmed the history of their symptoms and supervised a test to find out if they had coronavirus antibodies.

The study, published in PLOS Medicine, found that 77.6 per cent of 567 people with smell and/or taste loss had SARS-CoV-2 antibodies.

Of these 39.8 per cent did not have a cough or fever, and participants with loss of smell were three times more likely to have SARS-CoV-2 antibodies, compared with those with loss of taste.

Prof Batterham added: “Our research suggests a key public health message should be: people who notice a loss in their ability to smell everyday household odours such as garlic, onions, coffee, and perfumes should self-isolate and seek a coronavirus PCR swab test.”