Use loss of taste and smell as key screening tool for COVID-19, researchers urge

5th June 2020

King’s College London researchers have called for the immediate use of additional COVID-19 symptoms to detect new cases, reduce infections and save lives.

In a letter published in The Lancet, the team discussed how loss of taste and smell – anosmia – should form part of screening measures for the virus.

They said:

“As countries slowly emerge from lockdown measures, it is imperative to correctly contact-trace infected individuals. We believe that having added loss of smell and taste to the list of COVID-19 symptoms is of great value as it will help tracing almost 16% of cases that otherwise would have been missed.”

The team, led by Professor Tim Spector, previously reported that loss of smell and taste is a key predictor of COVID-19 in addition to the most established symptoms of a high temperature and a new, continuous cough. The relative importance of the extra symptom was however disputed by sections of the UK government when it announced it was including the extra symptom. This additional analysis of the COVID Symptom Study app data and its 3.7 million users sought to quantify the clinical value of recording loss of smell in the population.

From 76,260 people with symptoms who tested positive for COVID-19 up to 19 May, 28.5% never reported any fever or cough and 16% reported loss of smell but not fever or cough. The prevalence of loss of smell and taste was three-fold higher in individuals testing positive (65%) than in those testing negative (22%), the strongest single predictor of being infected, suggesting that people with loss of smell and taste should self-isolate for at least seven days or until they can be tested.

Professor Spector said:

We believe that loss of smell and taste is a very common COVID-19 symptom and in fact, occurs more often than fever and lasts longer (5 days on average compared to only 2 for fever). Infections could be reduced, and lives saved now that this non-flu-like symptom is widely recognised, and actions are taken.

The researchers suggest that policymakers should consider these findings and their implications for mass screening as part of other public health measures in key areas such as schools, hospitals, airports and care homes.

Professor Spector said:

“Our data suggests that low-cost so-called ‘smell the difference’ screening tests, that are already being used in some workplaces to screen people has they enter buildings, would capture a larger number of positive cases than temperature sensors do. We therefore feel that it should form part of a wider public health approach to reducing the infection rate.”

Loss of smell and taste a key symptom over fever for COVID-19 cases

1st April 2020

Losing your sense of smell and taste may be the best way to tell whether you have COVID-19, according to the latest analysis of the data collected by our COVID Symptom Tracker App

26% of the 1.5 million app users between 24-29 March 2020 reported one or more symptoms through the app. Of these, 1,702 reported having been tested for COVID-19, with 579 positive results and 1,123 negative results. 

The data analysed from the app shows that 59% of COVID-19 positive patients reported loss of smell and taste, compared with only 18% of those who tested negative for the disease. These results were much stronger in predicting a positive COVID-19 diagnosis than self-reported fever.  

Using all the data collected, the King’s College London research team behind the app alongside ZOE data scientists developed a model to identify which combination of symptoms together could predict COVID-19 cases. 

The model features a combination of loss of smell and taste, fever, persistent cough, fatigue, diarrhoea, abdominal pain and loss of appetite, in which the strongest predictor is loss of smell and taste. 

When applied to the +400,000 individuals reporting symptoms who had not yet had a COVID-19 test, the team found that almost 13% of them are likely to be infected by the virus – meaning an extra 50,000 individuals are likely to have as-yet unconfirmed COVID-19 infections. 

The app, which was developed by a King’s College London team in association with the Guy’s and St Thomas’ NHS Foundation Trust NIHR Biomedical Research Centre and a healthcare start-up ZOE Global LTD, asks users to log their symptoms (or lack thereof) daily.  

The aim is to help researchers understand the spread and progression of COVID-19. By 31st March 2020, more than 1.8 million users in the UK have signed up to help by logging their symptoms every day. 

Lead researcher Professor Tim Spector said: 

“When combined with other symptoms, people with loss of smell and taste appear to be 3 times more likely to have contracted COVID-19 according to our data and should therefore self-isolate for seven days to reduce the spread of the disease. 

This urgent research is only possible thanks to the 1.8 million citizen scientists logging their symptoms every day. This also gives us an evolving map of the UK of where symptoms are occurring two to three weeks before a strain on the NHS, which is why it’s vital to continue logging your health and symptoms, even when you feel completely healthy, and encourage others to use the app.” 

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