A new type of coronavirus test that is being widely used to detect people without symptoms had very low levels of accuracy at the University of Birmingham, UK, one of the few places where it was directly compared to a most accurate type of test in a real world environment.
Among students in Birmingham, only 3.2 percent of those infected with the virus correctly received a positive result from the lateral flow tests being used there, according to preliminary data from the university.
This is much lower than previously reported sensitivity levels for this type of test. The sensitivity was 57 percent when used in a mass screening pilot in Liverpool, UK, and more than 70 percent when verified in UK government laboratories, according to a spokesman for the UK Department of Health and Welfare. United Kingdom.
The first type of assay to be developed for coronavirus, called a PCR test, is more accurate. PCR tests indicate whether genes for the virus are present and are generally offered to people who have symptoms of Covid-19. Typically, tests must be sent to a laboratory for processing and may take a day or two to produce results.
Lateral flow tests, also called antigen tests, are a more recent development. They indicate whether certain viral proteins are present. Similar in design to home pregnancy tests, they can produce results in as little as 15 minutes.
Many organizations have begun testing people without coronavirus symptoms to try to prevent infections from spreading unknowingly. They often use lateral flow tests due to their rapid results. But concerns have been raised about its lower accuracy, especially around the "false negative" rate, when someone is told that no coronavirus can be detected, when they are actually incubating the virus.
The University of Birmingham was one of several educational institutions in the UK that offered lateral flow tests to all of their students before they returned home for the Christmas holidays. Approximately 7,200 accepted the offer during the first week of December, and a tenth of them, chosen at random, also received a PCR test to verify the accuracy of the lateral flow tests.
Lateral flow tests indicated that 0.03 percent of the students had the coronavirus. But in the smallest fraction that underwent a PCR test, the prevalence was much higher, 0.86%, according to figures published online this week.
It is unknown why the sensitivity of the lateral flow test was so low, says Jon Deeks of the university, who participated in the screening program. One factor could be that students took their own nasal and throat swabs, and may have done so incorrectly, although they did so under supervision, and self-swabs are also used by many other screening agencies.
It could also be an artifact of the small numbers involved, says Louise Kenny of the University of Liverpool. The level of PCR positivity came from 6 positive results among 710 students. "Statistically that doesn't make sense," says Kenny.
The tests are carried out by the American company Innova Group. A company spokesperson wrote by email that they are unaware of the data reported by the University of Birmingham. “The suggested low level of efficacy is not something we acknowledge, suggesting that a careful and thoughtful examination of the methodology used would be advisable. When used correctly, the Innova test is a very effective tool for detecting infectious people and allowing an adequate response to help reduce the spread of the SARS-CoV-2 virus. ”
The Birmingham coronavirus prevalence figure from lateral flow tests was much lower than that seen in other UK universities. For example, the University of Portsmouth found a prevalence of 0.2 percent among its asymptomatic students and the University of Reading 0.4 percent, according to a BBC report. But Edge Hill University in Lancashire found no positive cases out of about 2,100 students, according to the same report. It is not clear if these other universities asked students to swab themselves.
It is planned to introduce mass screening by lateral flow testing among all secondary school students in England from January. "They certainly shouldn't be used like this," says Deeks.
Allyson Pollock from the University of Newcastle in the UK says that mass screening using lateral flow testing should not have been widely introduced before testing its accuracy in the community. "They have not been evaluated outside of a laboratory."
A spokesperson for the UK Department of Health and Welfare said by email: “The country's leading scientists rigorously evaluated the lateral flow test and confirmed the accuracy. Our evaluation work and ongoing pilots are helping us understand how lateral flow testing works in the field and how we can use it to help stop the spread of the virus. ”
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