700,000 Covid-19 tests must be performed each week in France, but it’s hard to see clearly. Who will be tested and under what conditions? What tests are performed: the one that detects the presence of the virus or the one that detects antibodies? And by what procedures? Dr Michel Segondy, virologist at Chu de Montpellier, was the guest of France Bleu Hérault this Thursday morning
There are two very different categories of tests that do not measure quite the same thing. Can you explain us?
Exactly. The diagnostic test is the virological test by the technique called PCR, a technique which is very sensitive and which detects the genome of the virus in the sample. These samples must be well taken, be deep enough and be taken in the first days of the onset of symptoms. If the sample is not deep enough, if we just take it from the nostril and there, we do not touch the virus. So if the sample is well done, deep enough, and if it is done in the first days of symptoms, it is reliable. The number of what can be called false negatives will be very small. If it is too late or if it is poorly done there, of course, the sample loses its reliability. This test costs 54 euros, but it is reimbursed by health insurance.
Serological tests to detect antibodies have not yet been validated and are not reimbursed
There is the serological test. This is something else.
So the serological test is something else. This is a test that is done to identify antibodies against the virus that develop as a result of the infection. These tests are not yet validated, because there are many tests that are developed and not all have the same quality in terms of reliability of the result. We remember for example that in Spain, a very large number of tests had been bought in China and these tests were not worth much. So the, these are tests that have not yet been validated. Therefore, they are not reimbursed by Social Security. There are private laboratories that do them, but the patient pays for them. This test is of epidemiological interest to see how the virus has been spread in the population. This test has a retrospective interest because you will know if you have been infected or not.
It’s good to get tested today as soon as you have symptoms
Francine de Jacou’s question: when you have a start of cold symptoms, just a spot in your throat, a stuffy nose, should you call your doctor to get a test.
Indeed, as we actively monitor the circulation of the virus, as soon as you have evocative symptoms, that is to say often a simple cold, sore throat, fever, etc., you must actually screen. So there, normally, your doctor will prescribe a test that you can do in a city laboratory without problem. And in addition, there is now an application called Contact Covid, which also allows you to list all the contacts you may have had in the previous days, at family level, professional level, etc. So that all your contacts are also tested. And of course, there is a positivity, it will be necessary to isolate people so that they do not transmit the virus. So yes, in front of symptoms which can evoke the infection by the coronavirus, it is necessary to see his doctor and to be tested.
Is the key symptom fever?
Not systematically, fever is part of the picture, but there are forms where the fever is not very important. So after, these are mainly the respiratory signs, so sore throat, cough, runny nose. And then, the loss of taste and smell.
Question from Bernard to Lodève: if you go to your doctor and the doctor prescribes you, who gives you a prescription for a serological test. Will you not be reimbursed for this serological test that we will do in a private laboratory?
No, not for the moment. The serological test is not reimbursed. Only the virological test is reimbursed if prescribed.
Question from Jean to Castelnau le Lez: My question concerns the PCR test. If I have no symptoms, it seems to me that there is no point in taking the test because if I am negative today, I can be affected tomorrow and become positive tomorrow. And we are not going to do a test every day.
Exactly, therefore, we’re not going to screen all the people who are symptomless, then we know that generally the test will be positive within two days of the onset of symptoms. So, if you are asymptomatic and contactless, you will not be screened. But on the other hand, if you have symptoms and you are positive at that time, the people with whom you have been in contact will be able to be screened, even in the absence of symptoms because there are therefore often positive tests before symptoms appear.
Question from Luc de Béziers: I feel fit. But if I take the test and it is positive, what happens to me?
If you are in good shape and have no symptoms a priori, there is no need to take a test because there is a good chance that this test will be negative, unless you are really at risk, that is to say that you have been in contact with someone who has been positive. So, at this point, you can have the normal test, even if you are asymptomatic, and if the test is positive, you will have monitoring of your condition. But above all, you will have to isolate yourself so as not to transmit.
If the serology test is negative, chances are you have not been ill with Covid
Question from Gislaine de Sète: is the serological test reliable?
So, the serological test is reliable, but there are tests coming out on the market that have not yet been evaluated. This should happen fairly quickly. And so, there are tests that are very reliable and there are some that are much less so. And so, we are waiting for the national reference centers to validate the different tests and give the performance of the different tests to find out whether this or that test is reliable or not. For now, it is premature to say that such a test is valid or not.
Because I have been sick since March 15 and I had the test, it was negative for me when the doctors told me that I had had the coronavirus.
So you may have had the flu who has equivalent symptoms or another respiratory infection. The reliability of all tests is not yet known, but chances are you’ve had something other than Coronavirus.
Question from Gisèle in Saint-Pons-de-Thomières: there is a person who had diarrhea and loss of taste and temperature. It was tested negative. So my question is, does the coronna land only on the bronchi or can it land on the intestines?
With coronavirus, there may be digestive symptoms with diarrhea. It is not at all systematic since often what predominates are the respiratory signs. So, a priori, if the test is negative, there is a high probability that it is not the coronavirus. As I told you earlier, there may be cases where the test can be faulted depending on when it was done and how it was done.
Asymptomatic and healthy carrier, it’s the same thing
Is there a difference between what is called an asymptomatic carrier and a healthy carrier on which the virology would not be would not be detectable?
So no. It means the same thing. Asymptomatic or healthy carrier, it means that you are infected without having symptoms. So, either because the symptoms will appear a little later, we also know that asymptomatic forms do exist. Generally, asymptomatic people will only be screened if they have been in contact with someone who has been identified as infected.
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