[ad_1]
It doesn’t help that most of the coronavirus tests used in Norway are 99.9 percent specific, as it is called in technical parlance, which are therefore very accurate.
However, 1 in 1000 test results, which should have been negative, is positive.
Things can happen on the way from test to result, either in the lab or in analysis.
see more
– Now when we are in a situation with a low incidence of SARS-CoV-2 infections in the population and many of them are analyzed, many of the positive test results are false positives, says chief physician Kristoffer Hammer Endresen from the Department of Microbiology at Nordland Hospital Bodø.
However, he notes that most positive test results, which are related to flare-ups or when the person has been in other defined situations with an increased risk of infection, are real.
4 out of 5 false
In April, when the pressure of infection was significantly higher in society, more than 4,000 random people had to be tested to find a person with a truly positive test result.
The only problem is that there would be five positive results out of the 4000 tested.
– Therefore, four of the five test results would be false positives. With a completely random positive test result, it’s only a 20 percent chance that this represents an actual coronavirus infection, Endresen says.
However, when the uncontrolled infection situation in March-April forced Norway to close a large part of the company, it was tested in a different way than today.
The tests were largely reserved for people with symptoms. that at the same time he had been in a situation of real risk of infection.
– With such an approach, what we call pretest probability increases. So the probability of getting false positive results is considerably lower. Now it is highly dependent on people, even if they want a coronatest. So we have a bigger problem with false positives. For us in the lab, a positive test result can mean double duty, as someone who tests positive must take the test again to confirm the result, says Endresen.
– Must be retested
Based on this, Endresen believes that it is important to choose who it is appropriate to test.
The situation is different now than it was in mid-March, so basically everyone with respiratory symptoms should be offered a test, but to a greater extent to offer tests to people without symptoms, the superior believes that it is not a sustainable strategy. .
– We are now in a situation where we know that we get a lot of false positive results. The Norwegian Institute of Public Health recommends that people who have no symptoms or who have not been at risk of infection, but still test positive for covid-19, should be retested to confirm the result, says Endresen.
On May 25 this year, at a time when the spread of infection in Norway was very low, FHI published an article emphasizing that large groups of healthy people do not need to be tested when there is little infection with crown in the country.
– The Norwegian Institute of Public Health does not recommend testing large groups of healthy people for covid-19, such as all employees of a company. Now that there is little spread of the coronavirus in Norway, such tests serve no purpose, FHI stressed.
“If a person who has no symptoms or who is at higher risk of infection, and who lives in a society with little infection, is tested, it is very unlikely that the person will test positive. However, there is a high probability that a positive answer is false, that is, that the person who tests positive is really healthy. In the case of a very low infection in society, this applies even if the test itself is of good quality “, says the Article.
– 14 out of 15 false positives
Based on the good infection situation at the end of May, FHI made the following calculation:
Given the current infection situation in Norway, health professionals must test about 12,000 random people to find a positive case with COVID-19. In such a sample, there will be about 15 positive test results, but 14 of these will be false positives, said Dr. Joakim Øverbø at NIPH, emphasizing:
– In such situations, health professionals should not rely on a positive result until a new test has been performed to confirm it.
[ad_2]
