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More than 80% of people who tested positive in a national coronavirus survey did not have any of the core symptoms of the disease on the day they were tested, scientists say.
The finding has sparked fears that future Covid-19 outbreaks will be difficult to control without more widespread testing in the community for “silent transmission,” particularly in universities and high-risk workplaces such as processing facilities. meat.
The UCL researchers said that 86.1% of the infected people collected by the Covid-19 survey of the Office for National Statistics between April and June did not present any of the main symptoms of the disease, namely cough, fever or loss of taste or smell. the day they had the test.
Three-quarters of those who tested positive had no noticeable symptoms, the scientists found when they checked whether people reported other ailments, such as fatigue and shortness of breath, on the day of the test.
Unlike community coronavirus tests that target people with symptoms, the ONS infection survey routinely assesses tens of thousands of households across the country whether or not occupants have symptoms.
“At the moment the focus is on people who have symptoms, but if you don’t catch everyone who is asymptomatic or presymptomatic, it can be really difficult to reduce flare-ups early, before they get out of control,” said Irene Petersen. , author of the study and professor of epidemiology and health informatics.
While those who tested positive in the ONS survey may have developed a fever, cough, or other common symptoms, Petersen believes there is a risk of “silent transmission” from people who do not know they are infected.
The study, published in Clinical Epidemiology, looked at symptoms described by more than 36,000 people who were tested between April and June. Only 115 tests were positive and of those only 27 people, or 23.5%, had symptoms of any description.
When scientists narrowed down symptoms for the top three coronavirus infections, namely cough, fever, or loss of taste or smell, the number of people reporting the ailments dropped to 16% or 13.9%.
On the back of the findings, Petersen argues that universities and high-risk workplaces, such as meat processing facilities, should regularly test for people who may be infectious but show no symptoms. She urged colleges to increase testing capacity now so that students can be tested during the fall and, crucially, before they go home for Christmas. “Anyone who has had students come home for Christmas knows that they often bring some kind of bug with them and this particular Christmas they could bring Covid home and potentially sow new shoots,” he said.
Last month, the government’s Scientific Advisory Group for Emergencies (Sage) issued a similar warning, stating that there was a “critical risk” of large numbers of infected students causing outbreaks across the country when they returned home at the end of the period. .
Given the pressure on testability, Petersen said joint testing was needed, where the swabs are pooled and tested as a single lot. Since most people do not have the virus, most combined tests will be negative, but when a batch tests positive, contributors must be tested individually to identify the infected person.
Patrick Maxwell, director of the Cambridge School of Clinical Medicine, said the study underscored that many infected people are asymptomatic. “There will be a great public health benefit in terms of reducing transmission if we can reliably identify asymptomatic people and then self-isolate,” he said.
He said Cambridge was testing an approach that uses pooled samples to allow a “massive asymptomatic testing program” for students.
