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Lateral flow tests detect people at greater risk of spreading Covid, study claims


Lateral flow tests detect people at greater risk of spreading Covid and are more accurate than previously thought, study claims

  • Research found that lateral flow tests detect about 80% of positive Covid cases
  • Cotton swabs are 90% effective in detecting Covid when people are most contagious
  • Previous research underestimated their effectiveness, researchers say:

Lateral flow tests are better at detecting people at greater risk of spreading Covid and are more accurate than previously thought, a study has claimed.

British and American researchers found that rapid tests are 90 percent effective in detecting the virus in people who are most contagious.

And the smears — which have been criticized for both missing cases and producing false positives, especially when self-administered — are up to 80 percent effective at finding Covid in all people, the study found.

Lateral flows are the standard tests used in schools across Britain and are free on the NHS for people who have no symptoms.

Previous research has suggested that the tests — which can provide results in as little as 15 minutes — miss as many as 42 percent of asymptomatic people and 22 percent of symptomatic cases.

But most other studies compare lateral flow results to infections confirmed by a lab-based PCR test, which the researchers say is “comparing apples and oranges.”

Instead, they used a mathematical formula to recalibrate previous data to reflect the fact that lateral currents are designed to detect people who are actively infectious, not diagnose infection, as is the case for PCRs. .

Lateral flow tests are better at detecting people at greater risk of spreading Covid and are more accurate than previously thought, a study has claimed


Rapid coronavirus testing can miss four in 10 asymptomatic people, a large study completed earlier in the pandemic found.

Researchers who analyzed 64 studies of the effectiveness of lateral flow kits found that they failed to detect 42 percent of cases that showed no signs of disease.

The gold standard Cochrane review found that the tests, which give results in just 30 minutes, were better at detecting symptomatic cases (78 percent).

The findings have raised concern among some scientists, as it is thought that at least half of Covid transmission comes from healthy-looking patients.

Children are even less likely to get sick from the coronavirus, but they can still act as spreaders of the disease.

Hundreds of thousands of lateral flow tests are used every day on teachers and students to keep schools open and Covid-free. They are also used in care homes, hospitals and around the world companies.

Professor Jon Deeks, a biostatistician at the University of Birmingham and co-author of the report, said ministers may have rushed lateral flow tests in schools “without any corroborating evidence from the real world.”

The review also found that lateral flow tests were prone to giving false positives when a test says someone is infected, but they aren’t.

Lead author Professor Irene Petersen, an epidemiologist at University College London, said it makes little sense to use PCR testing as a ‘gold standard’ compared to lateral currents.

She said: “Previous studies comparing the reliability of lateral flow tests and PCR tests could potentially be misleading, because a PCR test is a marker of infection at some point within a certain time frame and does not necessarily mean someone is contagious.” positive during testing.

‘In most validation studies, individuals were tested simultaneously with LFTs and PCR tests, using PCRs as the gold standard for saying someone is ‘positive or negative’.

‘The sensitivity of the LFTs was therefore assessed for their ability to identify the same cases that the PCRs picked up.

“However, this is comparing apples to oranges.”

Researchers reviewed the data on how long people are infectious and used it to derive the formula to recalibrate the test efficacy data.

They estimate that of the group that tested positive for a PCR but was asymptomatic and missed by lateral currents, only half would have been infectious.

Therefore, previous studies estimating lateral currents that were less than 50 percent effective at detecting Covid likely significantly underestimated their effectiveness, the researchers said.

Professor Michael Mina, an epidemiologist at Harvard University, said: ‘There is a spectrum of contagious amounts of the Covid virus and we show that LFTs probably detect cases 90 to 95 percent of the time when people are most contagious. .

The tests could even reach 100 percent sensitivity when viral loads are at their peak and therefore capture almost anyone who currently poses a serious risk to public health.

“It’s very likely that if someone’s LFT is negative, but their PCR is positive, it’s because they’re not at the maximum transmissible stage.”

Professor Petersen added: ‘As LFTs are widely used in schools, workplaces and to access venues such as those used for major events, it is important that health professionals and the public have clear information about the performance characteristics of the tests.

‘We have shown that the absolute sensitivity to detect SARS-CoV-2 antigens is probably high in LFTs.

“To improve our understanding of their characteristics, longitudinal studies where individuals, and ideally contacts of cases, are tested daily by LFTs and PCR tests would help to identify false negatives (and false positives) and, most importantly, the time differences between the turning PCR positive, LFT positive and the onset of symptoms.’



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