Rapid tests less sensitive but detect the most infectious, claims study

RAPID turnaround coronavirus tests could be used to detect the most infectious people and potentially help when it comes to relaxing lockdown restrictions, scientists have suggested.

Researchers at the University of Oxford said they had, for the first time in a large-scale study, confirmed that the more virus detected in a person’s nose and throat – known as viral load – the more infectious that person was.

The accuracy of lateral flow tests had been called into question by some experts, but the Oxford researchers said that these rapid tests could be most useful in picking up people with the highest viral loads. Scientists said their study, which used information from more than a quarter of a million people who had taken part in test and trace, suggested that, overall, just six in 100 contacts of people who tested positive went on to become infected.

They said of the 303,192 contacts in their study, 18,291 (6 per cent) tested positive between two and seven days after the date of their index case’s (the contact who had first tested positive) test. People with the highest viral loads are the most important to detect quickly and isolate, to stop them passing on the virus, the researchers said.

They concluded that the lateral flow tests, while “less sensitive” than the standard lab-processed PCR tests, could be effective in quickly detecting the most infectious cases in a relatively cheap way. Tim Peto, professor of medicine at the University of Oxford, said: “We know that lateral flow tests are not perfect, but that doesn’t stop them being a game changer for helping to detect large numbers of infectious cases sufficiently rapidly to prevent further onward spread.”

Dr David Eyre, at Oxford’s Big Data Institute, said: “When the time comes to relax the lockdown restrictions, by rapidly identifying the most infectious people using these lateral flow tests, we can potentially relax the lockdown much more safely.”