This would enable more people to qualify for a “gold standard” PCR nasal and throat swab test and increase the number of positive diagnoses from 69 to 96 per cent, they said.
At present, the “classic” symptoms of Covid are loss of sense of smell and taste, fever and new persistent cough.
But the King’s research said that, because many people were displaying symptoms outside the “classic triad”, they were then unable to secure a test, and thus not being diagnosed.
Researchers at King’s and the Coalition for Epidemic Preparedness Innovations (CEPI) analysed data from more than 122,000 UK adult users of the ZOE app.
They found that app users were more likely to report headache and diarrhoea within the first three days of symptoms, and fever during the first seven days – showing that different symptoms emerged at different stages of the disease.
App data also showed that 31 per cent of people with Covid didn’t have any of the three classic symptoms in the early stages of the disease, when they are most infectious.
Cough or dyspnoea (shortness of breath) were reported by 46 per cent of within the first three days of symptoms. There is growing understanding that the spread of Covid variants is causing different symptoms, with the dominant Kent variant more likely to result in a persistent cough.
Professor Tim Spector, from King’s, who has led the roll-out of the app, said: “We’ve known since the beginning that just focusing testing on the classic triad of cough, fever and anosmia misses a significant proportion of positive cases.
“We identified anosmia as a symptom back in May and our work led to the government adding it to the list, it is now clear that we need to add more.
“By inviting any users who log any new symptoms to get a test, we confirmed that there are many more symptoms of Covid-19. This is especially important with new variants that may cause different symptoms. For us, the message for the public is clear: if you’re feeling newly unwell, it could be Covid and you should get a test.”
They also said that the new symptoms differed by age – with headaches being reported in children aged five to 17.
Today’s findings, published in the Journal of Infection, may be of value in countries beyond the UK where testing is limited, by allowing greater certainty in which symptomatic patients to test.
It also suggests that millions of cases have gone unconfirmed or delayed because of restricting tests to people displaying the classic three symptoms.
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Zoe app users have reported more than 14 possible or likely symptoms of Covid.
Professor Sebastien Ourselin, from King’s, said: “”The identification of this combination of symptoms through the Covid Symptom Study app is another prime demonstration of the value of big data analytics and mobile health technology to support the management of this pandemic.”
Dr Claire Steves, of King’s, said: “There are many symptoms which occur in acute covid, including some like fatigue and headache which are also common in other conditions.
“Depending on the testing available, different symptom combinations can be used to be as sensitive or specific as possible. We hope these models are of use in a range of settings – from vaccine trials to detecting and treating covid outbreaks going forward.”