Paris (AFP)

A patient capable of infecting tens or even hundreds of people? Discussed, the concept of "super-contaminator" of viruses remains partly an enigma for doctors, as the different transmission factors are difficult to unravel.

The concept of those which are called in English the "super-spreader" was not born with the Covid-19, it has already been used for example during the two other deadly epidemics with coronavirus, the Sras (2002-2003) or the MERS (ongoing since 2012). The term has resurfaced several times in favor of the current epidemic which, which started in China, has spread around the world.

"It is not a medical term", it is used to designate "a person who infects a proportionally very large number of individuals" without necessarily having a precise threshold, explains to AFP Amesh Adalja, medical specialist emerging infectious diseases and pandemic preparedness at Johns Hopkins American University.

Since the beginning of this epidemic at the end of December, at least two people have been nicknamed in the media "super-contaminators" (we also say "super-propagator"): it is estimated that they have contaminated more people than the average, which is two to three infected per patient, in the absence of control measures (confinement, limitations on gatherings, etc.).

This is the case of Steve Walsh, a British businessman returning from Singapore, responsible for around ten infections in February, including five in France. Recovered since, the man whom popular British newspapers had dubbed the "super-spreader" had then contaminated five other people on his return to England.

In South Korea, she is a sexagenarian nicknamed "patient 31", who is suspected of having infected dozens of people, notably through a religious rally in February.

But the concept is full of uncertainties and variables, point out a number of specialists: how to know what is related to biological characteristics specific to the patient, his behavior, his environment, or even the people he infected, the "hosts" , perhaps particularly vulnerable? How can you be sure that it is one and the same person who is the source of all infections?

Another unknown is the role of children - less seriously affected by the coronavirus but nevertheless vectors of the disease - in the contagion. It is precisely because there is fear of their ability to potentially infect many people that many countries, including France, have closed schools.

"It is possible that there are what are called" super contaminators ", that is to say patients who do not contaminate two or three people (...) but who can contaminate dozens," said Thursday evening on the LCI television channel, Pr Eric Caumes, head of the infectious and tropical diseases department at the Pitié-Salpêtrière hospital (Paris).

"The problem is that we can't spot them," he continued.

"It seems that certain patients, and without this being correlated with the intensity of the symptoms, excrete much more virus than others and therefore transmit more", also said to AFP Professor Olivier Bouchaud, head of the infectious diseases at the Avicenne hospital in Bobigny.

But, he nuances, "it is only a hypothesis currently, and obviously we do not have a clear explanation at this stage, which is moreover not specific to Covid-19".

- "All different" -

"We are all different in terms of our immune systems, our behaviors and where we move. All of these can play a role in the number of people we can infect. Biological and behavioral factors can be factors, but also time and place, "said Christl Donnelly, professor of statistical epidemiology at Imperial College London and the University of Oxford.

Uncertainties which even make say to Dr Bharat Pankhania, specialist of the infectious diseases of the faculty of medicine of the British university of Exeter, that "it does not exist, a + super-spreader".

For him, it is an "inappropriate term". "What we have are the circumstances that have led to the infection of more people," he said, referring to the case of "Patient 31" in South Korea.

And it is "often the crowd, a confined place with little ventilation, a faulty infection control, (...) and often a person at the beginning of his illness, when the secretions are maximum", he says again.

It is for these reasons that many prefer to speak of "situation of super-propagation" ("super-spreading event" in English) rather than to qualify a person of "super-propagator", a term moreover qualified of "stigmatizing "by the French Minister of Health Olivier Véran.

© 2020 AFP