Less than one week before the start of the Winter Olympics in Beijing, three of Norway’s cross-country skiers are in isolation in Italy. But even out of the required isolation period, one unpredictable value – one number – can be what causes the house of cards to collapse.
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For not only is a given number of days in isolation an obstacle, practitioners must also submit four negative tests during the last five days before departure.
And here it can be curly. Because when it is stated that one or more practitioners have taken a so-called PCR test, there is one thing you look at to judge whether the person is healthy or not.
This value is called CT, more on that later.
Heidi Weng and Anne Kjersti Kalvå became the first two cross-country skiers with positive corona tests. According to local rules in Italy, Weng and Kalvå will be in isolation for ten days – until Thursday 3 February.
The next day came the news that Simen Hegstad Krüger had also tested positive, he will stay one day longer than Weng and Kalvå.
These three may series of some of the competitions during the Olympics. Daniel-André Tande tested positive on 18 January and Johann André Forfang tested positive on 20 January. The may series throughout the Olympics.
How long the virus stays in the body is absolutely crucial, and the answer to that is completely impossible to give.
And then we are back to the CT value. Because in a so-called Polymerase Chain Reaction test, ie PCR, the answer is given in CT.
The Chinese Olympic Committee has set a CT limit value of 35. If the virus is not detected after 35 cycles, you are thus considered healthy and allowed to participate in the Olympics.
– With a threshold of 35 rounds, they have pushed it quite far. If you get something then, it is very little in the first place. Then the Chinese in practice require negative tests, says professor of molecular immunology, Anne Spurkland, to VG.
Previously, there was a requirement for a CT value above 40, but it was last week changed to 35.
– I would say that is a pragmatic and sensible difference. If they demanded 40, it would be a very extreme line, says Spurkland.
The PCR test confirms or refutes the corona by looking for the virus’ genetic material. This is done by running the sample through a machine. CT stands for “cycle threshold”, ie how many cycles the machine must run before it finds traces of the coronavirus.
If the sample contains a lot of virus, the machine needs fewer cycles for the virus to be detected. Thus, the CT value becomes low.
If the sample contains little virus, the machine needs several cycles for the virus to be detected. Thus, the CT value becomes high.
You must therefore deliver four samples that have a higher CT value than 35 during the last five days before departure, in order to be allowed to travel at all.
Then to the impossible math. Because even if you are symptom-free and feel healthy, the virus can remain in the body for a long time.
In fact, it is completely individual how long the virus remains in the body. Ergo, two people who have been infected at the same time can test negative at different times.
When the CT values first exceed 35, it should in principle be safe to test negatively on the following days as well.
It (the CT values) will not jump up and down, but it is with a small reservation that there may be some variation in how the virus is detected on the swab. There is a slight difference in how efficiently it is collected, says Spurkland.