Cell biologist: PCR COVID-19 tests might be too accurate

Drive-through testing in Ida-Viru County.
Drive-through testing in Ida-Viru County. Source: Sergei Stepanov/ERR

The PCR tests currently used to test people for COVID-19 requiring a medical professional, are time-consuming and can be inconvenient. The counterweight however is high accuracy, which might not be so important in all cases.

Coronavirus tests based on PCR (polymerase chain reaction) will give a positive result even if there are very few virus particles in the sample. Toivo Maimets, professor of cell biology at the University of Tartu, explained that virus particles are reproduced via chain reaction until they are easier to notice. For illustration purposes, Maimets said the process is like making one gram of sugar into 33 tons.

"If the sample is taken from the nasal cavity and there is one virus particle for one microliter, the PCR test will discover it. Perhaps that one particle does not do anything to us, there is just not enough of it," Maimets noted.

"There is a whole row of articles that say that less than 1,000 particles per microliter is not clinically relevant. It does not develop a clinical picture, does not develop spread. In other words, our PCR-test is seemingly 1,000 times more sensitive than it needs to be," he added.

This can lead to asymptomatic and non-infectious people to give positive tests. Maimets emphasized however that there is no final confirmation on whether or not asymptomatic people spread the virus or not.

The Health Board values the sensitive tests because it helps discover the virus at an early stage. Lili Milani, research professor at the Estonian Genome Center of the University of Tartu, is studying if samples could also be taken from saliva.

"There is research that shows that saliva or a mouthwash could give similar results as tests taken from the nose. If we are thinking of monitoring studies, where specific schools are tested, mass testing conducted in cities or schools, where we want to think about other conditions - inconvenience and so on, the [test] sensitivity does not fall short," Milani said.

Taking samples from saliva means it does not have to be seen through by a medical professional, which would also be cost-effective. The Health Board is also using non-PCR rapid antigen tests when complete testing care homes. Toivo Maimets said there is still a lot of uncertainty when it comes to testing and further research results must be studied.

"New methods to detect the virus - saliva, nose cavity, sewage - these methods are being developed around the world. At very panically high speeds in order to make the tests faster, cheaper and more trustworthy. These are the three most important factors," Maimets noted.

"It is always important that the effectiveness of these methods must be checked and that takes time, it takes this numb daily scientific work. Noone wants to do the work, everyone wants to get results tomorrow" Maimets concluded.


Follow ERR News on Facebook and Twitter and never miss an update!

Editor: Kristjan Kallaste

Hea lugeja, näeme et kasutate vanemat brauseri versiooni või vähelevinud brauserit.

Parema ja terviklikuma kasutajakogemuse tagamiseks soovitame alla laadida uusim versioon mõnest meie toetatud brauserist: