Categories
Publications

Nucleic acid testing (NAT) technologies that use real-time polymerase chain reaction (RT-PCR) for detection of SARS-CoV-2 – WHO

WHO has received user feedback on an elevated risk for false SARS-CoV-2 results when testing specimens using RT-PCR reagents on open systems.

As with any diagnostic procedure, the positive and negative predictive values for the product in a given testing population are important to note. As the positivity rate for SARS-CoV-2 decreases, the positive predictive value also decreases. This means that the probability that a person who has a positive result (SARS-CoV-2 detected) is truly infected with SARS-CoV-2 decreases as positivity rate decreases, irrespective of the assay specificity. Therefore, healthcare providers are encouraged to take into consideration testing results along with clinical signs and symptoms, confirmed status of any contacts, etc.

https://web.archive.org/web/20201215013928/https://www.who.int/news/item/14-12-2020-who-information-notice-for-ivd-users

Categories
Opinion

PCR-based COVID testing has failed and is not a proper basis to lockdown the nation, let alone decide on tiers for restrictions – Mike Yeadon, Lockdown Sceptics

Briefing paper for MPs authored by:

  • Clare Craig BM BCh FRCPath
  • Jonathan Engler MBChB LLB
  • Mike Yeadon BSc Hons (Biochem-tox) PhD (Pharmacol)
  • Christian McNeill LL.B and Dip LP

Stop mass-testing using PCR in the UK and replace with Lateral Flow Tests where required. If we are correct, this single measure alone will cause a sudden drop in “cases” (as seen in Liverpool) and allow the UK to return to normal life within weeks.

Other recommendations as detailed later in this document. It should be noted that legal cases and technical challenges to PC

https://lockdownsceptics.org/wp-content/uploads/2020/11/MP-briefing-26-Nov-2020.pdf

Categories
News

How accurate are the covid tests? – Sebastian Rushworth M.D.

And that, ladies and gentlemen, is why PCR positive cases are a very poor indicator of how prevalent covid is in the population, and why we should instead be basing decisions on the rates of hospitalization, ICU admission, and death. If we just look at the PCR tests, we will continue to believe that the disease is widespread in the population indefinitely, even as it becomes less and less common in reality. And that is assuming the rate of testing doesn’t increase. If we combine this built-in problem with accuracy, with a massive increase in testing (as has happened in most countries over the course of the pandemic), then we can create the impression of a disease that is continuing to spread wildly through a population, even when it isn’t.

https://sebastianrushworth.com/2020/11/06/how-accurate-are-the-covid-tests/

Categories
Opinion

The problem with Covid testing – Spiked

Clare Craig is a consultant pathologist and expert in diagnostic testing. She has raised concerns that inaccurate Covid test results may be producing a skewed picture of the nature and course of the pandemic – a picture based on overestimates of cases and deaths, and underestimates of immunity levels. spiked caught up with her to discuss what has caused the problems in testing, how they are manifested in the data, and where the government has gone wrong in its Covid strategy.

  • There has been so much pressure put on laboratories, there have been flaws in the results of the tests they are doing.
  • People who have been diagnosed with Covid who did not have Covid.
  • We are testing at such a large scale – over 200,000 tests per day – that even a small percentage of mistakes ends up meaning large numbers of people being affected.
  • The SAGE committee has an overrepresentation of physicists, chemists and mathematicians.
  • For people from those backgrounds, false-positive test results are usually related to highly precise laboratory equipment. In those cases, the false-positive rate is a stable number.
  • It’s not like that in medicine. For the test kits, the false-positive rate is stable. But for the process as a whole, there are all sorts of things that can go wrong. That includes problems with cross-contamination, and problems with cross-reactions with other viruses.
  • Things have gone wrong because of the UK’s strategy for testing.
  • In an epidemic, there are two strategies that you take, one at the beginning, and then one when you reach peak deaths.
  • When you increase the number of tests you do, you start to find milder cases.
  • Factors show that Covid has become less severe.
  • Normally, we would start to see increasing numbers of influenza cases at this time of year. But influenza seems to have disappeared globally.

https://www.spiked-online.com/2020/11/05/the-problem-with-covid-testing/

Categories
News

The statistical quirk that means the coronavirus pandemic may never officially end – The Telegraph

If you are starting to feel like the coronavirus epidemic will never end, then you may be correct. A statistical quirk in testing means that Britain may never hit zero cases, even if the virus is wiped out entirely.

The reason lies in the large number of false positives that are almost certain to creep in once case numbers drop very low, yet testing remains very high.

Testing is never 100 per cent accurate, and scientists must factor in the false positive and negative rates when determining infection prevalence. The problem is, nobody knows what those rates are.

The best guess at present is that coronavirus tests pick up around 80-85 per cent of positive cases, and around 99.9 per cent of negative cases.

https://www.telegraph.co.uk/news/2020/08/12/statistical-quirk-means-coronavirus-pandemic-may-never-officially/

Categories
News

Antibody tests do not pick up people who had mild coronavirus, Oxford study suggests – The Telegraph

Antibody tests may be missing large numbers of people who contracted Covid-19 because they don’t work for people who had a mild infection, new research from Oxford University suggests.

A study of more than 9,000 healthcare workers suggested significant numbers of people were getting ‘negative’ test results, despite probably having had the virus.

https://www.telegraph.co.uk/global-health/science-and-disease/antibody-tests-may-miss-people-had-mild-symptoms-coronavirus/

Categories
Publications

Interpreting a covid-19 test result – BMJ

No test gives a 100% accurate result; tests need to be evaluated to determine their sensitivity and specificity, ideally by comparison with a “gold standard.” The lack of such a clear-cut “gold-standard” for covid-19 testing makes evaluation of test accuracy challenging.

A systematic review of the accuracy of covid-19 tests reported false negative rates of between 2% and 29% (equating to sensitivity of 71-98%), based on negative RT-PCR tests which were positive on repeat testing. The use of repeat RT-PCR testing as gold standard is likely to underestimate the true rate of false negatives, as not all patients in the included studies received repeat testing and those with clinically diagnosed covid-19 were not considered as actually having covid-19.

Further evidence and independent validation of covid-19 tests are needed. As current studies show marked variation and are likely to overestimate sensitivity, we will use the lower end of current estimates from systematic reviews, with the approximate numbers of 70% for sensitivity and 95% for specificity for illustrative purposes.

https://www.bmj.com/content/369/bmj.m1808

Categories
Publications

Variation in False-Negative Rate of Reverse Transcriptase Polymerase Chain Reaction–Based SARS-CoV-2 Tests by Time Since Exposure – Annals of Internal Medicine

However, new research from Johns Hopkins University (MD, USA) has found that the chance of these tests giving a false negative – stating no infection when the individual actually is infected – is greater than 1 in 5, at times being far higher. The study, which analyzed seven previously published studies that evaluated RT-PCR performance, calls into question the accuracy of the predictive value of such tests.

Biotechniques, 29 May 2020

https://www.acpjournals.org/doi/10.7326/M20-1495