How a false 'negative' test may hinder fight against COVID-19

New Delhi, Apr 11: COVID-19 has wrecked havoc across the globe killing more than one lakh people but nobody knows how many undetected cases are out there.

Many countries have limited testing to the old or with pre-existing conditions, refusing test for others with milder symptoms that can nevertheless spread the virus.

As the numbers surge scientists have warned about a growing concern: Many people with negative results might actually have the virus, leading to devastating implications.

Even though the World Health Organisation has proposed 'testing' as key strategy to fight coronavirus, no test is perfect. Most of the times doctors and clinical experts struggle with test accuracy all the time, across all areas of medicine.

In the particular scenario, the majority of tests around the world use a technology called PCR, which detects pieces of the coronavirus in mucus samples.

But "there are a lot of things that impact whether or not the test actually picks up the virus," news ageny AFP quoted Priya Sampathkumar, an infectious diseases specialist at Mayo Clinic in Minnesota.

"It depends on how much virus the person is shedding (through sneezing, coughing and other bodily functions), how the test was collected and whether it was done appropriately by someone used to collecting these swabs, and then how long it sat in transport," she said.

The virus has only been spreading among humans for four months and therefore studies about test reliability are still considered preliminary.

Early reports from China suggest its sensitivity, meaning how well it is able to return positive results when the virus is present, is somewhere around 60 to 70 percent.

Why do false negative tests exit?

As of today, tests done in the US for COVID-19 use a technique called PCR, which detects pieces of the coronavirus in mucus samples taken from a patient. PCR works well, and it will flag a sample as positive even if there are only a few copies of the virus in it.

The problem is that the virus doesn't tend to stay in an easily accessible part of the body. It lurks in the nasopharynx, where the back of the nose meets the top of the throat. To test someone for the new coronavirus, doctors and nurses have to stick a very long swab very deep into their nose. Many false negative test results are probably because the swab wasn't done correctly.

Doctors also don't know when in the course of a COVID-19 illness the test works best. The data on the test's false negative rate jumbles together all of the tests that have been done.

So, if you have coronavirus symptoms, assume you have the illness even if you test negative.