The two tests that will help to predict spread of Covid-19

One detects past infection, the other finds current viral load – but there’s a shortage of staff trained to carry them out

Only by implementing carefully controlled programmes that use two very different Covid-19 test kits will it be possible to predict how the disease will affect the country, researchers have revealed.

Scientists emphasised the need to understand, as quickly as possible, where and when new cases of infection were appearing. At the same time, it was vital to pinpoint individuals who had already been infected, possibly without realising it, so that scientists could understand the disease’s behaviour over the coming months. Two different tests would be able to achieve these separate goals.

To locate those in the first category – the newly infected – medical staff need to use a polymerase chain reaction (PCR) test, which can find viral particles on a person. The test locates a particular coronavirus gene sequence and creates multiple copies that can then be easily detected.

To identify those who have already been infected and who should now be immune from reinfection, doctors need to use a test that shows antibodies generated in response to a past infection of Covid-19 .

Andrew Preston, of Bath University, said that the PCR test was in itself very effective for detecting the virus but that that efficacy was dependent on how well healthcare workers took samples from patients, from the nose and the back of the throat.

“If a virus is not picked up on the swab, the result will be negative. Thus, how effectively the swab is taken, and the amount of virus present at the sampling sites, will determine whether the virus is detected from an infected person,” he said.

More testing is to be carried out, after Michael Gove’s announcement that healthcare workers in England will be tested from this weekend, starting with critical care doctors and nurses. However, there is a shortage of PCR machines, of staff trained to use them and, most worryingly, of reagents needed to run them. That will limit the uptake of the tests.

The PCR test will be used as the disease continues to spread this year, but over the next few months we will see the introduction of antibody tests. The government has announced that it is buying 3.5m of these tests, which are now being evaluated at Oxford University.

“Testing people across the country to find if they have been infected by Covid-19 will tell us precisely how the disease is behaving,” said Professor Adam Finn, of Bristol University. “This will create certainty about where we stand and about the measures we need to take to limit the spread of the virus. At present we are in the dark. That should stop once we get the antibody test up and running.”

Contributor

Robin McKie

The GuardianTramp

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