Mass coronavirus testing could prompt new infections and give a false sense of security

Mass coronavirus testing to allow relatives to visit care homes, or students home for the holidays, could give a false sense of security and lead to new infections, scientists have warned.

Researchers from the London School of Hygiene and Tropical Medicine (LSHTM) have been studying whether widespread testing could be useful at bringing down case numbers.

In Slovakia, where mass testing was rolled out to the population in October alongside a national lockdown, case numbers fell rapidly, they discovered.

However, they said it was difficult to unpick how much was the result of the restrictions and how much was due to testing.

While the researchers said mass testing could be useful in picking up asymptomatic cases which ordinarily might be missed, they warned it should not be used to provide an assurance that someone is not infected.

Last week it emerged that mass testing in Liverpool had missed half of positive cases.

Dr Stefan Flasche, associate professor at the LSHTM, said: “I think what people have been criticising is the use of the rapid test for allowing people to see high risk individuals. 

“So, testing students to allow them to subsequently see their parents or testing people who wanted to visit their older relatives in elderly care homes, in that case, a test can give a false security, because the test will not be 100 per cent clear that you will not infect someone else.”

Universities have set up temporary testing centres at which hundreds of thousands of students will be checked for Covid-19 before they leave for the holidays. Students have been asked to take two tests, three days apart.

Likewise, the Government has said that rapid lateral flow testing will be available to care homes by Christmas following pilots across the country.

Community testing will also soon be available for all local authorities in Tier 3 and the Government has suggested people could be allowed to visit pubs and meet friends if they test negative twice.

However, results published by the Government last week from the pilot scheme in Liverpool show that, compared to the usual polymerase chain reaction (PCR) tests, lateral flow tests picked up just five out of 10 positive cases.

In an opinion piece for The Telegraph, Dr Susan Hopkins, a senior medical adviser to PHE and NHS Test and Trace, said that the tests were extremely useful for quickly spotting asymptomatic cases.

“We know that between one in four and one in three people who have coronavirus never show any symptoms, but that does not mean they are not infectious,” she said.

“These devices can help identify people who have high levels of virus who do not have symptoms and would not otherwise be coming forward for a test.

“They are one of the tools we can use to reduce the risk of transmission in care homes. They need to be used in conjunction with PPE and other infection control methods to keep residents, their loved ones and staff safe.”

However, Dr Alexander Edwards, associate professor in Biomedical Technology, Reading School of Pharmacy, at the University of Reading, said proper messaging was needed so that people understood what the test results meant.

“Even if they receive a negative result, this doesn’t mean they are necessarily ‘safe’ as they could be incubating an infection, or the test might have been a false negative,” he said 

“All tests must be used as part of a wider, coherent public health strategy, that can make full consideration of accuracy and usefulness.”

Prof Sian Taylor-Phillips, professor of Population Health, University of Warwick, also said it was difficult to tell whether mass testing worked, because it usually runs alongside lockdown or tougher restrictions, which also rapidly bring down case numbers.

Commenting on the Slovakian results, she said: “This is similar to the initial data from Liverpool, where all areas with lockdown decreased their number of infections, and this decrease appears to be similar in areas with and without mass testing.

"There are lots of things that can affect the rate of infections so it’s very hard to interpret these findings.

“In this study from Slovakia, people who tested positive on mass testing did not receive a PCR test to confirm whether they did or did not have coronavirus, so we do not know how many people were detected by the mass testing, or how accurate the test was.”