"Our random sample study showed that around half of everyone who tested positive were residual-positive – this means that they had the disease some time in the past. Even though these people test positive in PCR tests, it does not mean they are infectious in that moment," Kalda explained.

"And even though we cannot directly apply these results to daily health statistics because people chosen at random constitute a different group than those who are referred to testing by family doctors and other medical professionals, we believe there is a fair number of people in whose case we cannot say whether they are infectious upon testing positive. It is possible they have recovered some time ago," she added.

At the same time, what happens next is currently based solely on isolating the person and looking for people they might have had close contact with.

"We need to consider whether we have the capacity to test every close contact and asymptomatic person in a situation where we are seeing a lot of new positives every day. Perhaps we should rethink how to move forward with testing, who to test and how to proceed in terms of isolation and identifying close contacts, as well as concerning other policies," the scientist said. "And another thing – perhaps we should be looking at other things besides a positive PCR test result when it comes to asymptomatic people," she added.

When it comes to asymptomatic people whose PCR test comes back positive, it is very difficult to say when they might have been infectious, Kalda emphasized.

That is why she believes a debate is in order on how to proceed – how many people to test, who should be tested and whether mass testing is even necessary.

"I believe we need to quickly identify and test people who are sick and who develop symptoms right away – isolate them," the professor said. However, this is often not possible as not everyone lives near a testing center. "It takes time for the person to go in to get tested after which it might again take quite a bit of time to get the results back, while people have several contacts in the meantime," Kalda said, giving the example of Maardu that lacks a nearby testing site and the residents of which simply decide not to get tested even though they have had close contacts with others.

"It is always important to concentrate on trying to identify those who are definitely infectious and isolating them post haste. But what to do in a situation where we know that window is difficult to pinpoint in case of asymptomatic Covid-positive people as PCR tests are very sensitive and can pick up residual results?"

"I am trying to figure out a way to make testing easily available to everyone. We have options," Kalda explained. "We must also consider what to do with close contacts and asymptomatic people. I would raise these questions, while I admit there are no immediate answers," she said.

"We place in isolation people whose PCR test is positive. However, we do it once their positive result is in. That is also when we start looking for close contacts. However, if the person was residually Covid-positive, close contacts happened much earlier. That is to say we are isolating these people at the wrong time. It is another point we need to make and discuss," the professor concluded.

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