'Classic triad' of symptoms misses positive COVID-19 cases, study finds
New research led by researchers at King’s College London suggests that restricting testing to the ‘classic triad’ of cough, fever and loss of smell which is required for eligibility for a PCR test through the NHS may have missed cases. Extending the list to include fatigue, sore throat, headache and diarrhoea would have detected 96% of symptomatic cases.
A team of 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 COVID Symptom Study app. These users reported experiencing any potential COVID-19 symptoms, and 1,202 of those reported a positive PCR test within a week of first feeling ill.
While PCR swab testing is the most reliable way to tell whether someone is infected with the SARS-CoV-2 coronavirus that causes COVID-19, the analysis suggests the limited list of three does not catch all positive cases of COVID-19.
Testing people with any of the three ‘classic’ symptoms would have spotted 69% of symptomatic cases, with 46 people testing negative for every person testing positive. However, testing people with any of seven key symptoms - cough, fever, anosmia, fatigue, headache, sore throat and diarrhoea - in the first three days of illness would have detected 96% of symptomatic cases. In this case, for every person with the disease identified, 95 would test negative.
Researchers also found users of the Symptom Study App were more likely to select headache and diarrhoea within the first three days of symptoms, and fever during the first seven days, which reflects different timings of symptoms in the disease course. Data from the ZOE app shows that 31% of people who are ill with COVID-19 don’t have any of the triad of symptoms in the early stages of the disease when most infectious.
Source: King's College London, 17 February 2021