Loss of smell could be a 'highly reliable indicator' of Covid-19, research says

The researchers, based in the United Kingdom, wrote in their study that people who lose either smell or taste should consider self-isolating, even if they have no other 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," Rachel Batterham, of University College London and University College London Hospitals, who helped lead the study team, said in a news release on Thursday.

The team studied 590 volunteers who experienced a new loss of smell or taste, and they tested 567 of them for Covid-19.

Among those 567 people who were tested, 77.6% tested positive for Covid-19 antibodies. In total, 80.4% of participants reporting smell loss and 77.8% of those reporting taste loss had a positive test result, the researchers reported in the journal PLOS Medicine.

About 40% of those who tested positive for antibodies had neither a fever nor a cough.

Batterham and her colleagues also found that participants with loss of smell alone were nearly three times more likely than patients with just a loss of taste to have Covid-19 antibodies, and participants with a combined loss of smell and taste were four times more likely to have antibodies.

"These findings suggest that a loss of smell is a highly specific symptom of Covid-19, in contrast to a loss of taste, despite their comparable frequency," the researchers wrote in the study.

The study recruited its volunteers between April 23 and May 14, during the peak of the Covid-19 outbreak in London. The findings come with some limitations, including that the study does not include a comparison group of people who did not lose their sense of smell and/or taste.

Overall, the loss of smell -- called anosmia -- emerged early on in the pandemic as a possible Covid-19 symptom. In May, it was added to the official list of coronavirus symptoms in the United Kingdom, the Department of Health and Social Care announced.

At the time, a government statement said that "all individuals should self-isolate if they develop a new continuous cough or fever or anosmia."