Loss of smell a ‘highly reliable’ indicator of Covid-19 infection: Study

Scientists say the findings, published in PLOS Medicine, show that an acute loss of smell or taste is a ‘highly reliable’ virus indicator and should now be considered globally as a criterion for self-isolation, testing, and contact tracing.

The cohort study, which assessed health data from primary care centres in London, found that 78% of people who reported sudden loss of smell and/or taste at the height of the pandemic had SARS-CoV-2 antibodies. Of these people, 40% did not have a cough or fever. It is the first time such a figure has been calculated.

Lead author, Professor Rachel Batterham (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.”

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 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 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 three times more likely to have SARS-CoV-2 antibodies, compared with those with loss of taste.

Professor 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.”

While 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 had suggested a prevalence of smell and/or taste loss in the range of 31-85% in Covid-19 patients. This is the first study to accurately establish the proportion of those who had experienced loss of smell and or taste as having COVID-19.

The study was funded by the National Institute for Health Research Biomedical Research Centre at UCLH, where Professor Batterham is Obesity Theme Director.