Scientists are calling for an urgent investigation after dozens of reports of people testing negative for Covid gold standard PCR tests, despite testing positive for rapid lateral flow tests and, in many cases, experiencing symptoms similar to those. of Covid.
The United Kingdom Health The UKHSA said it had learned that people in some areas of the country anecdotally reported positive lateral flow test results with subsequent negative PCR tests, and that it was investigating the cause.
The scientists told The Guardian that they would like more done to ensure that members of the public that they may be infected with the virus are not falsely assured that it is safe for them to mix with other people.
Alan McNally, a professor of microbial evolutionary genomics at the University of Birmingham, who helped establish some of the Lighthouse labs, state-funded Covid-19 testing facilities, said: “You need the government to send really clear and immediate messages. what test about [people should] be guided by. My very clear advice would be that if you have a respiratory infection, stay home because you are going to catch it.
“But if you have symptoms of a respiratory infection and a lateral flow test that is positive, you would be assuming it is Covid-19 regardless of the PCR result at this point. That message needs to be clear, which then buys time for the Department of Health and UKHSA to do a quality audit of the PCR testing process and try to find out where the problem may be. “
Dr Kit Yates, Senior Lecturer in Mathematics at the University of Bath, said: “I would suggest that this be investigated with the utmost urgency. In the meantime, people who test positive for lateral flow devices (LFDs) should isolate themselves if they can. An additional independent positive LFD test will help confirm a positive Covid diagnosis, despite a negative PCR test. Lack of ability to claim [financial] Supporting isolation without a positive PCR test further emphasizes the need for urgent problem resolution. “
Anecdotal reports have suggested that the problem may be more widespread in south-west England, prompting speculation that a new variant of Sars-CoV-2 could be the cause. However, physicians in Manchester and Oxfordshire have also reported discrepancies between lateral flow and PCR test results, and scientists believe that a new variant is unlikely to occur.
McNally said: “The vast majority of PCR testing being done in the UK targets three parts of the viral genome, and the idea that a new variant would emerge that falls for all three targets is just not going to happen. There is also a huge level of genome surveillance, which would have detected this. “
The UK Health Safety Agency also said that there is no evidence of a new variant emerging, and that existing variants have been tested with LFDs in use, which continue to perform to expected standards.
Although no Covid-19 test is 100% accurate, the number of reported cases suggests that something else may be going on. “I don’t think that mathematics explains all these cases. Especially what is happening in the Southwest, and in particular cases where there are multiple LFD positives followed by multiple PCR negatives, ”Yates said.
Professor Oliver Johnson, Director of the Institute for Statistical Science at the University of Bristol, said: “The key to me is that the proportion of LFTs that passed the repeat PCR test (where an individual’s LFT is confirmed by a PCR test) fell into last week’s test and trace the report, when it really shouldn’t have, given the prevalence [of the virus.]”
Another theory is that lateral flow tests, which detect a coronavirus protein called a nucleoprotein, are mistakenly reacting against the nucleoprotein of a different seasonal coronavirus. Although possible, this is also considered unlikely.
Rupert Beale, who heads the Infection Cell Biology laboratory at the Francis Crick Institute in London, said: “There is a wide potential cross-reactivity with seasonal coronaviruses, but at least in the UK they are tested for this against three of the four seasonal coronavirus. “
The fourth, HKU1, has not been tested because it is difficult to grow this virus in the laboratory. Although it can trigger symptoms of the common cold, which include shortness of breath, cough and runny nose, other symptoms similar to those of Covid are less common, although fever, chest pain and gastrointestinal symptoms are sometimes present.
Still, McNally thinks another explanation is more likely: “If we rule out a new strain and rule out cross-reactivity, that points to something within the PCR testing process. It can be anywhere from the swab being taken to the test being performed and the result being spread.
“I hope someone is looking lab by lab at the results and the data they are producing.”
Susan Hopkins, UKHSA’s chief medical adviser, said: “If you get a positive LFD test, it’s important to make sure you get a follow-up PCR test to confirm you have Covid-19. If you have symptoms of Covid-19, isolate yourself and perform a PCR test. With any test, it is important to carefully read and follow the test kit’s instructions for use to avoid incorrect readings. “