UK study finds loss of smell most reliable indicator of Covid-19

An acute loss of smell or taste is a "highly reliable" coronavirus indicator and should now be considered globally as a criterion for self-isolation, testing, and contact tracing, according to a research by UK scientists.

The cohort study, which assessed health data from primary care centres in London and is published in ‘PLOS Medicine' this week, found that 78 per cent of people who reported sudden loss of smell and/or taste at the height of the pandemic had SARS-CoV-2 or COVID-19 antibodies. Of these people, 40 per cent did not have a cough or fever. According to experts, it is the first time such a figure has been calculated.

"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,” said lead author professor Rachel Batterham, from University College London (UCL) Medicine and UCL Hospitals.

"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,” said Batterham.

"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,” she said.

Recruitment to the study took place between April 23 and May 14 at the peak of the pandemic 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 per cent of 567 people with smell and/or taste loss had SARS-CoV-2 antibodies; of these 39.8 per cent 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.

"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," Batterham said.

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 per cent in COVID-19 patients. This is the first study of its kind to try and 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 Batterham is Obesity Theme Director.