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Infectious Diseases

Updated 10 June 2020

More emphasis on accuracy of tests vital before Covid-19 pandemic can be fully contained

A new paper points out more evidence that false negatives through coronavirus tests are a concern.

  • New research from Dartmouth emphasises the implications of false negative tests
  • Numerous false negatives have been reported in RT-PCR tests
  • More emphasis on accuracy and a standardised process is needed 

On 29 May 2020 Health24 published an article on the possible repercussions that false negatives for coronavirus could have in containing the spread of Covid-19.

According to the latest research published in the Annals of Internal Medicine, the odds of a false negative through RT-PCR, the most commonly used test, is one in five.

Now, further research from the Geisel Medical School of Dartmouth suggests that even more emphasis should be placed on addressing these inaccuracies, as testing is crucial to containing the pandemic.

Testing inaccurate in two ways

According to lead author, Prof Steve Woloshin from the Geisel School of Medicine at Dartmouth and of the Dartmouth Institute for Health Policy and Clinical practice, there are two ways in which the current diagnostic tests, which involve a swab from the nasal passage, can be inaccurate:

"A false-positive result mistakenly labels a person infected, with consequences including unnecessary quarantine and contact tracing. [Secondly], false-negative results are far more consequential because infected persons who might be asymptomatic may not be isolated and can infect others," he stated in a news release.

Lack of standard process

In the paper published in the New England Journal of Medicine, the team from Dartmouth refer to several current limitations of the RT-PCR tests. This includes a difference in the sensitivity of the tests and the lack of a standard process to validate the accuracy of the tests

The researchers also concluded that testing can only be part of an efficient strategy to contain the epidemic and that a standard should be set for all tests. Right now, there is no standard process, according to the study authors.

What can go wrong if tests are not accurate?

In a previous article, Health24 spoke to Dr Glenda Davison, laboratory expert and head of the Biomedical Sciences Department at the Cape Peninsula University of Technology about the implications in South Africa if we experience false negatives.

According to her, it’s a difficult situation as there are many factors that can contribute to false negatives and inaccuracies, including the fact that the sampling from a nose or throat swab isn’t always adequate.

She also stated that the inaccuracy of tests has negative consequences for the effectiveness of track and trace screening.

“In many cases, tests are being performed on people who do not have any symptoms, but who have been in contact with a positive individual. If it is in the early stages (days one to four), or the specimen is not processed properly, they could very well test negative and not go into quarantine. This could, of course, lead to increased spread unless all contacts are made to self-isolate irrespective of a test result,” she stated.

No laboratory test fool-proof

According to Dr Davison, the current limitations of tests shouldn’t be a reason for us to become complacent with the current efforts in place.

"However, these tests also have their pitfalls. In the meantime, it is important that we are all aware of the limitations of the RT PCR test and that false negative results are possible,” Professor Davison said.

More effort needed

The research team from Dartmouth drew several conclusions from their study. Diagnostic testing will help in safely reopening countries while controlling Covid-19, but this strategy can only work if the sensitivity and accuracy of tests are increased.

They also stated that there should be a standardised process and that the FDA should provide full details of the tests’ clinical sensitivity.

Dr Davison also stated that, as infections in South Africa increase, there should be more awareness of the fact that tests could result in false negatives. She stated that screeners should know that these false negatives can happen, as well as the reasons why they happen.

READ | Scientists warn of false-negative results with Covid-19 virus tests – what are the implications for SA?

READ | Latest on Covid-19 testing in SA: Public sector backlogs more than 6 days – an expert tells us more

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