“I tested positive last Monday and I have a party scheduled for next Tuesday.
I will always be positive?
Like many other people, you may have asked yourself this kind of question recently.
An epidemic recovery has begun and the number of French people testing positive for Covid-19 every day has increased sharply, from 20,000 to more than 40,000 in two weeks.
In reality, it is not at all impossible to test positive twice 8-10 days apart.
“On average, the virus is detectable in nasopharyngeal swabs 2 or 3 days before the onset of symptoms and approximately 7 to 10 days after”, details the National Institute of Health and Medical Research (Inserm).
“Half are still positive on D10 or D12”
A head of medical analyzes in central France went through the statistics in his laboratory.
“When people have tested positive by antigen test or self-test, around half of them are still positive on D10 or D12.
At D20, around 10% are still positive, and 20% with a PCR test
(much more sensitive than an antigen test)
”, he replies.
From a month of difference between two positive tests, it is very likely that it is a reinfection.
An American study, conducted on a very small sample, gives slightly different figures.
Less than a quarter of people infected with Omicron were still positive by PCR test at D7.
"A negative PCR on D7, personally, that makes me wonder about the sampling technique", is surprised Stéphane Korsia-Meffre, medical writer for Vidal.
“I have even known people who are still positive after five weeks by PCR test, because there is still virus in their nose”, abounds François Blanchecotte, president of the union of biologists.
Read alsoEpidemic rebound in France: what do the recent waves in South Africa and Portugal teach us?
What impact does this have on isolation?
Take the case of a person vaccinated or who already had the Covid less than four months ago.
According to the rules established by the Ministry of Health and by the Health Insurance, she must isolate herself for seven days if she tests positive.
This period begins on the day on which the symptoms appear or, in the absence of disorders, on the day of the positive sample.
This duration can however be shortened: if a second test carried out on the 5th day is negative and if the person no longer has symptoms, the isolation can be lifted.
If this second test is positive, the isolation is maintained until the 7th day, i.e. two more.
Important clarification: "It is not necessary to carry out a new test on the 7th day".
"Infected but not necessarily able to transmit"
Under these conditions, a person who decides to be tested again on the 7th or 8th day and who is still positive would therefore no longer have to isolate themselves, according to these rules.
“A positive test means that you are infected, but not necessarily able to transmit the virus.
Antigenic or PCR tests detect viral components, but not the infectious virus as such,” underlines virologist Vincent Maréchal.
“You can absolutely have viral RNA lying around, even if it is neutralized”, adds François Blanchecotte.
A test can then prove positive for a very long time, especially if it is a PCR, as indicated above.
But isn't this period of 7 days of isolation (maximum) a little too short?
Some scientific work on the Omicron variant could suggest this.
According to a Japanese study prepublished last January, for example, the viral load (and therefore the ability to transmit the virus) is maximum between three and six days after the onset of symptoms.
It is only after the tenth day that it decreases significantly.