- In France, several dozen new cases of coronavirus have been diagnosed since Thursday.
- "We have before us an epidemic that is coming" and we will have to "face it at best," said Emmanuel Macron on Thursday.
- For the moment, the health authorities have not announced where the first French contamination came from.
How to find the "patient zero", this first person infected with a pathogen? This is one of the challenges faced by doctors who are trying to trace the first person affected by this new virus in France. Because for the moment, we still do not know how the two patients living in the Oise were infected. The only clue: they live and work within a radius of 40 km.
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Where does the term come from?
Don't talk to Anne-Marie Moulin about “stalking”. "To say that we are" looking for "the first patient for scientific reasons, yes. But in general, we "hunt" an animal during a hunt, or we "hunt" a suspect ", explains the CNRS Paris 7 emeritus researcher at the Sphere laboratory" Sciences - Philosophy - History ", also a doctor and philosopher.
Why don't we rather say "patient 1"? "The" patient zero "was employed for the first time with regard to AIDS, and more particularly Gaëtan Dugas, this Canadian steward of a thousand lovers, accused of having" caused death on the planet "", says she. An accusation which dates from 1987 and which was corrected thirty years later by a study published in 2016 in Nature, which rehabilitated the memory of this man. "There was a scientific aspect, but also a moral one," says the researcher. Apparently, initially, he would have been called a sick patient O, with the letter O for "Out of California". The spotlight was then shone on the homosexual community of California. We would therefore have confused the O with the zero. "
Why is it essential to find this person? Because she can spread the virus to other individuals in her business, at her children's school, on public transport… Especially if she does not know that she is sick. This may be the case for this coronavirus, which sometimes results in cold symptoms, when the patients are not asymptomatic ... "It is a rather banal epidemiological approach, which has two objectives. Scientist, to better understand the disease and how it is transmitted. And medical, to avoid transmissions, continues the researcher. This is why we must contact the patient and his entourage to monitor and possibly treat them. It is an approach that has nothing to do with finding culprits. There is therefore the same survey which searches for patients upstream, the “zero patients”, but also downstream, the “patient contacts”, his relatives, who have been infected.
Identify "contact cases"
How is the investigation going? As soon as a person is hospitalized for a Covid-2019, he is contacted by the ARS on which his hospital depends and must answer a precise questionnaire to retrace his journey since the onset of symptoms. "We take into account the hospital route, and we interview the entourage, colleagues, relatives, family, to reconstruct the course of the last 14 days of the infected person," said Jérôme Salomon, Director General of Health , at a press briefing on Wednesday. This procedure is called " contact tracing ". "The medical team is also on the front line to ask questions of the family or the person if they are aware:" what have you done in the past month? " "Who did you see?" "Continues Anne-Marie Moulin.
A unique process? “This search for contact cases is always the same, whatever the epidemic, we are assured to the Ile-de-France Regional Health Agency, in charge of the investigation for the Oise. What is not standardized is the questionnaire, carried out a few days ago by the ARS and Santé Publique France. The notion of the level of contagion of the disease is essential: the index of contagiousness of the coronavirus is between 1.5 and 3.5 [which means that an infected person contaminates on average between 1.5 and 3 , 5 other people], that of measles at 9. Logically, the research will therefore not be of the same magnitude.
An investigation that can be a puzzle. "People's fear of the contagion can lead them to overstate the risk," warns the researcher. Evaluating the time and the proximity in a queue in front of a bakery, it's complicated… ”In addition, the link with animals could play an important role in these investigations, since in China, the virus was probably born in the bat, and was able to pass through the pangolin. A plausible hypothesis, but not yet verified. "For Ebola, theoretically, it was a 2 year old boy who was the" zero case ". We supposed that he had had contact with a bat while playing in a tree in Guinea in 2013, ”said the researcher.
Three levels of risk
On the downstream side, then, the “contact cases” are closely followed by the epidemiologists of the Regional Health Agency, who pilot these surveys in France. They respond to "standardized protocols" and countries regularly discuss them, under the aegis of the WHO. Internationally, the process has been used in other epidemics: Sras in 2002-2003, Mers in 2012-2013, or Ebola in 2014. Once identified, these people are contacted by telephone and classified according to their risk level: "negligible", "low", or "moderate to high".
In the first case, nothing is done. Then, "if the risk is low, we will tell the person that they have to watch themselves. She has a phone number at the ARS which she must reach if she has symptoms, but otherwise, she does not change anything in her life, we are told at the ARS Ile-de-France. Third scenario: people who spent more than an hour within one meter of the patient. They are placed in solitary confinement and must take their temperature and call daily, even if they do not have a fever. "
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