Massive screening of the population is one of the strategies put in place by the State to control the Covid-19 epidemic. With nearly 1,3 million PCR tests performed per week in France, this type of screening is the most used in the country. How is the test carried out? Is he reliable? Is it taken care of? All the answers to your questions about the PCR test.

The PCR (polymerase chain reaction) virological test can be used to determine whether a person has the virus at the time of the test. It consists of identifying the presence of the SARS-CoV-2 virus (responsible for the Covid-19 disease) in the person’s body, more precisely in his upper respiratory tract.

The test consists of inserting a flexible cotton swab (swab) in each nostril up to the nasopharynx for a few minutes. This process is unpleasant but not painful. The sample is then analyzed in the laboratory using a method called “polymerase chain reaction” (PCR). This technique makes it possible to detect the RNA of the virus, its genome, which in a way characterizes it. According to the French National Authority for Health (HAS), the best time to detect SARS-CoV-2 RNA is 1 to 7 days after the onset of symptoms. Before or after this period, the PCR test would no longer be optimal.

Availability of results

The result is usually available within 36 hours of collection. But due to the large number of people wishing to be tested at the moment, this period may be longer, especially in large cities.

While waiting for the results of the test, the patient must remain confined at home and imperatively respect the barrier gestures.

PCR tests are carried out in screening centers. The list of centers set up throughout France is available on the sante.fr site or on the site of your Regional Health Agency (ARS). On the sante.fr site, users can find the contact details of each sampling point, information on schedules, slots for priority people, waiting time, etc.

The Covid-19 screening strategy

As the Covid-19 screening strategy has intensified since the first deconfinement (May 11, 2020), anyone can be tested today. It is indeed possible to be tested with or without a medical prescription since July 25. But, faced with the congestion of medical analysis laboratories which leads to an extension of the deadlines for making an appointment and results, the government has decided to make the test a priority for certain people:

• those with symptoms of the disease;
• contact cases;
• those with a medical prescription;
• nursing or similar staff.

On its website, the government indicates that “for these audiences, dedicated test time slots have been set up in the laboratories”.

Positive PCR test without symptoms of Covid-19

A positive test means that the person is a carrier of the SARS-CoV-2 virus. In the absence of symptoms or if the symptoms are not serious, the patient must remain isolated until recovery, i.e. at least 7 full days after the appearance of the first signs of the disease and 2 days after the disappearance of the disease. fever. It is up to the doctor to specify the end of the isolation. In addition, surgical masks are prescribed to the patient, at the rate of 2 masks per day for the duration of the isolation and a work stoppage will be provided if necessary to cover the period of isolation.

Positive PCR test with symptoms of Covid-19

For people who test positive (whose symptoms are not serious) and who share their room, kitchen or bathrooms with other people, the doctor may suggest that they go to a specialized hospital during the isolation period in order to not to contaminate them.

Finally, in the event of a positive test in a person presenting serious symptoms, in particular difficulty in breathing, this person will be immediately hospitalized.

In the event of a negative PCR test, the procedure is different depending on the case.

If the person has taken the test because they showed signs of Covid-19, they must continue to strictly adhere to the barrier gestures, especially if they are among those considered to be at risk for the virus (elderly people, people suffering from a chronic disease…). The negative result means that she was not a carrier of the virus at the time of the test but not that she is protected against the disease (she can still catch the virus).

As part of a “contact case”

If the person has been tested because they have been identified as a “contact case”, they must remain in isolation until the patient is cured if they live with it and both must repeat the test 7 days after recovery. In the event of a second negative test, the isolation can be lifted. If the person who took the test does not live with the sick person (s) with whom they have been in contact, the isolation ends when the negative test result is received. Barrier gestures and the wearing of a mask must still be strictly observed.

The nasal PCR test is the most reliable to date, with a reliability rate of over 80%. However, there can be false negatives when the sample is not correctly taken:

• the swab was not pushed far enough into the nostril;
• the screening was not done at the right time (between the 1st and the 7th day after the onset of the first symptoms).

The case of false positives

There may also be false positives (the person is diagnosed positive even though they are not a carrier of the virus). But they are very rare and often linked to a problem with the reagent used during the analysis of the sample.

The PCR test costs € 54. It is 100% covered by Health Insurance, whether you do it with or without a medical prescription. Most of the laboratories that practice it exempt from the advance of fees, so patients do not have to pay anything. However, some testing centers may ask to advance the costs. These are reimbursed on a care sheet (to be sent to your health insurance fund).

PCR tests are the most widely used today because they are the most reliable. But there are other tests to detect the SARS-CoV-2 virus:

Serological tests:

They make it possible to determine the presence of antibodies in the blood that the body would have produced in reaction to the virus. If the serological test detects antibodies in the person tested, this means that he or she was a carrier of the virus, but the result does not allow us to know when the contamination dates from.

Antigenic tests:

As with the PCR test, the antigen test consists of a nasopharyngeal swab. But unlike the PCR test, it does not detect virus RNA but virus specific proteins also called antigens. The result is obtained faster than for the PCR test because the sample does not need to be sent to the laboratory.

It is placed on a strip containing antibodies which bind to the desired antigens then the result appears within 15 to 30 minutes. According to the HAS, these tests are recommended when PCR tests are not available, when the delays in obtaining the results of a PCR test are too long, and preferably in people with symptoms or contact cases of a confirmed case. (symptomatic or not).