Loss of smell a ‘highly specific’ indicator of Covid-19, finds UCLH and UCL research

Acute loss of sense of smell should be considered globally as a criterion for self-isolation, testing, and contact tracing for Covid-19 infection according to researchers at UCLH and UCL.

The call came after a study of people in the community with acute smell and/or taste loss at the height of the pandemic in London found 78% had SARS-CoV-2 antibodies. It is the first time such a figure has been calculated. Of these people, 40% had neither cough nor fever.

The study, published in PLOS Medicine and led by Professor Rachel Batterham (UCL Centre for Obesity Research, Division of Medicine and UCLH) found that participants with loss of smell were 3 times more likely to have SARS-CoV-2 antibodies compared with those with loss of taste.

The study was funded by the NIHR UCLH Biomedical Research Centre, where Prof Batterham is Obesity Theme Director.

It has been known for some time that Covid-19 can cause loss or reduced ability to smell (anosmia) or taste, without cough or fever. Existing data suggest a prevalence of smell and/or taste loss in the range of 31-85% in Covid-19 patients.

For this study, researchers looked at a group of people in the community with loss or smell and/or taste, to see how many had antibodies. Since a high proportion of this group had antibodies, this suggests smell and/or taste loss is highly predictive of a COVID-19 infection.

Although self-isolation and testing on the basis of smell or taste loss alone is recommended in the UK, at a global level few countries recognise loss of smell and/or taste as symptoms and advise testing and self-isolation. The majority are focused on fever and respiratory symptoms. Researchers said this must change in order to reduce the spread of the pandemic.

Recruitment to the study took place between 23 April and 14 May 2020 by sending text messages to people registered with a number of primary care centres in London who had a new 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 telemedicine consultation with a healthcare professional who confirmed the history of their symptoms and supervised a test to find out if they had SARS-CoV-2 antibodies.

A total of 77.6% of 567 people with smell and/or taste loss had SARS-CoV-2 antibodies; of
these, 39.8% had neither cough nor fever, and participants with loss of smell were 3 times
more to have SARS-CoV-2 antibodies, compared with those with loss of taste.

New loss of smell was more prevalent in participants with SARS-CoV-2 antibodies, compared with those without antibodies (93.4% versus 78.7%).

Professor Batterham 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 disease spread.

“Acute loss of sense of smell needs to be considered globally as a criterion of self-isolation, testing, and contact tracing.

“Our findings suggest that a key public health message is that people who notice a loss in their ability to smell everyday house-hold odours such as garlic, onions, coffee, and perfumes should self-isolate and seek PCR testing.”