who, when and where to test

Since the massive screening of Covid-19 was set up in France and elsewhere, laboratories have been taken by storm, but there is confusion over the protocols to be followed depending on the country. France 24 examines the health directives for the two main types available – virological and serological.

Faced with fears of a second wave, many countries have opted for massive screening for Covid-19 to quickly isolate each new source of pollution and avoid new containment. France and Britain have thus chosen to draw inspiration from the German, New Zealand and Taiwanese models, three countries praised for their handling of the pandemic before the summer.

>> Read also: the European tour for health measures

But the massive screening quickly led to endless queues outside doctors’ offices and laboratories. Between Augustans returning from holidays and airlines demanding that their customers present negative tests, the test centers have quickly been “saturated”.

Overwhelmed and tired, health care professionals also condemned the general confusion over the screening protocol. In the United States, for example, health officials said in late August that people who were exposed to positive cases of Covid-19 finally did not need to be tested if they did not show symptoms. Prior to the outcry over this announcement, the director wanted to clarify the minutes by confirming that “screening can be considered” for contact matters. A wording that was considered unclear which largely contributed to confusing the message to the public.

Test all or priority cases

In fact, the guidelines for conducting a screening test are determined based on the epidemic in a particular country, but also depending on the capacity of the equipment.

If the stock is limited, authorities may decide to test only subgroups of suspected cases, according to the European Center for Disease Prevention and Control (ECDC), an EU body. The ECDC recommends prioritizing hospital patients with severe respiratory infections, symptomatic healthcare professionals and the elderly with underlying chronic diseases.

Several countries, which have generated sufficient stocks, now encourage the entire population to be tested, even if individuals do not show symptoms. This is the case with France, which in August announced support for tests to encourage the French to be tested. But laboratories and screening centers overwhelmed by demand prioritize people with symptoms, “contact cases” and those who have prescriptions.

In the UK, the National Health Service has recommended testing only people with symptoms or those who have been asked to do so. “This will make it easier for people who need a test to do it,” he explains.

Virological or serological?

Among the two major tests offered in Covid-19 screening centers, we must distinguish between the virological PCR test (which means Polymerase chain reaction in English), performed by inserting a stick [sorte de très long coton-tige] in the patient’s nose to detect the presence of the virus, the serological test performed, him, from a blood test. The latter detects antibodies to know if the person has been infected before, even if they have not shown symptoms.

However, this serological test is not useful for people who have had symptoms for less than a week. It takes seven to fourteen days to develop antibodies.

At this time, researchers have still not been able to determine whether an individual can be infected twice with Covid. They also do not know if antibody levels drop over time so that they cannot be detected.

According to a study by the British company Cochrane, serological tests detected only 30% of people with Covid-19 one week after the first symptoms. Accuracy increased during the second week (70%), as well as the third (over 90%), before declining in the following weeks.

For this reason, people who are tested within eight days after the onset of symptoms are recommended to do a PCR test, as it detects the virus rather than the antibodies.

However, according to some studies, one in five PCR tests may result in a “false negative”, which means that the individual is a carrier of the virus but the test did not detect it. In question: human error during the test or poor timing, the virus is not present in the nose during the entire disease. For this reason, many experts recommend repeating PCR tests, especially if symptoms persist.

Ten days of isolation

People who show symptoms are encouraged to do a PCR test as soon as possible and remain isolated while waiting for the result. The same goes for those around him, who also test if the result is positive.

In cases of more limited exposure, such as having a drink with a person who then tests positive, the person then becomes a “contact case” and must wait seven days before taking the PCR test to allow the period. incubation of the virus and avoid “false negatives”. Those whose PCR test is negative but who develop symptoms should retest.

Those who test positive should stay at home for at least ten days until all symptoms go away.

Health officials in most countries currently require two consecutive negative PCR tests, performed 24 hours apart before a patient returns to normal life.

The World Health Organization (WHO) also says that people can be considered recovered and non-communicable ten days after the onset of symptoms, provided they have no symptoms for three days.

This article is adapted from the English version, available here.