'A one-off test is a folly': The truth behind covid false negative covid results

When Sarah found herself suffering sudden bouts of breathlessness in May, she took herself to hospital. But after her COVID-19 swab test came back negative, doctors said she was probably anxious, and sent her home.

Despite this, Sarah’s symptoms continued to worsen. A week later, she was rushed to hospital in an ambulance. Paramedics told her that based on her clinic observations, she should be in a coma.

Then came more surprising news: She had tested positive for coronavirus

Sarah’s story – given to a patient safety charity under a pseudonym – is one that resonates with Dr Claudia Paoloni, president of the Hospital Consultants and Specialists Association. She detailed another case in which a patient tested negative twice: once when she was first admitted to hospital and once later in her hospital stay. She finally tested positive on her third test – by which time she was on a ventilator in intensive care.

Paolini believes COVID-19 swab tests produce a troublingly high rate of false negative results, and the problem lies in the reliance on a single test.

“To use as a one-off test in any capacity to exclude someone from having COVID-19 is a folly.” 

If you want to exclude someone from having the virus, Paoloni said, you must do multiple tests and collect multiple negative results. “If the test and tracing system is not working, which is the case here, transmission will continue unabated in the community.”

The most recent data published by the Office for National Statistics says the test’s sensitivity - which it says can tell us how likely it is to return a false-negative result, may be somewhere between 85% and 98%. 

Dr Deenan Pillay, Professor of Virology at University College London and member of Independent Sage, a group of scientists providing transparent advice during the crisis, said a significant number of self-administered tests could be coming back negative for people who do in fact have the virus.

“The single biggest reason why a swab from someone who has COVID-19 comes up as negative is the quality of the swab that is taken,” Dr Pillay said. “Swabbing your nose and throat in a way that will pick up the virus means really scraping down the side of the wall of the nose or back of the throat to get cells from the lining of the throat. That’s not a pleasant thing to do.”

This is of course true for at-home testing, which relies on the patient or a family member to collect the swab. But it could be true at testing centres, too.

Tom, a 29-year-old from London whose name has been changed for this story, said there were no medical staff on site when he visited a Covid testing centre in London. The only people he interacted with were staff from a third-party contractor paid to carry out testing.

“The man simply handed me a test, read out the instructions to self-administer the test, and asked me to do it myself,” he said.

Pillay agrees that testing methods are likely to have an impact on false negative results. “I have seen the documentation given out at testing centres and it is very confusing,” he said. “Centres often expect you to administer the test yourself or get someone else in your car to administer it for you, all of which creates difficulties.” 

Pillay believes the solution lies in having medically trained staff at testing centres. “The way the system is developed at the moment, outsourced to private companies like Deloitte and Lighthouse Labs, is just woeful,” he said.

“The whole system is failing at the moment. And it’s happening just as the numbers of infections are starting to rise,” Dr Pillay said.

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Source: Huffpost, 27 September 2020