Correcting the misconceptions around COVID-19 testing

The message from the World Health Organisation in combatting the COVID-19 crisis has been “test, test, test.”

World Health Organisation head Tedros Adhanom Ghebreyesus said there has not been an ‘urgent enough escalation in testing, isolation and contact tracing’.

He said testing should be the ‘backbone’ of the response to the pandemic.

As we have reported over the last few weeks, health tech companies are developing COVID-19 test kits at an accelerated rate.

The theory behind more efficient testing, is it enables reaching the peak of infections faster, therefore lockdown measures can begin to be relaxed.

For frontline workers, efficient testing means that those who present symptoms of COVID-19 can be tested, with a negative result allowing staff to return to caring for patients.

With the demand for testing increasing exponentially, Dr Jessica Watson took to Twitter to outline and bring clarity to some misconceptions around COVID-19 testing.

Dr Jessica Watson said:

“So much in the media about #COVIDー19 testing, it seems important to correct some misconceptions.”

“Two types of test: Viral RNA tests – RT-PCR – swab tests – to detect current infection.”

“Antibody test – serology – blood tests – to detect previous infection.”

“No test gives perfect 100% accurate results. Tests need to be evaluated to determine their sensitivity and specificity. More evidence here is needed – hence this call.”

“Let’s assume 2% of the population is infected with Covid-19, and 50% of these have fever.”

“If background prevalence of fever is 1% then anyone with fever has a 50% chance of having Covid-19 i.e. pre-test probability is 50%.”

“If viral swab tests are around 70% sensitive 95% specific then a patient with fever (pre-test probability estimate 50%) who has a negative test still has a 24% chance of having the virus.”

“The take home message is that if you have Coronavirus symptoms – then assume you have Coronavirus – even if your test is negative.”

“This is especially important for NHS workers who are now getting prioritised for testing – they risk being super-spreaders if they are falsely reassured by a negative test.”

“Yes, we need to test, test, test in order to understand the spread of this pandemic and to plan the appropriate public health measures to reduced spread.”

“But testing is not a panacea and without the correct interpretation of test results, false positives could do significant harm.”

You can see Dr Watson’s full Twitter thread here: