Announced on Saturday by the provincial government of Hubei, the case of a 70-year-old Chinese who contracted Covid-19 is enough to challenge. The septuagenarian would indeed have developed the symptoms of the coronavirus having already killed more than 2,300 people only after an incubation period long of 27 days, as reported by a Reuters dispatch this Saturday. In contact with his sick sister on January 24, he didn't get a fever until Thursday. The next day, the presence of the virus was detected in his body.
Such a delay is abnormally long compared to the estimates on which the scientific community currently agrees. "Today, all the estimates converge towards an average incubation period of 6 days and a maximum of 12 days," says Arnaud Fontanet, head of the epidemiology unit for emerging diseases at the Pasteur Institute. "Based on the information we have about other coronaviruses like MERS and SARS, this incubation period could be as long as 14 days," added the World Health Organization.
A study already suggests a duration of 24 days
This consensus should not be called into question by the single case of the 70-year-old Chinese man from Hubei. "There may be, exceptionally, longer incubations," says Arnaud Fontanet, head of the epidemiology unit for emerging diseases at the Pasteur Institute. The epidemiologist emphasizes that one should first be sure that the septuagenarian was not in contact with another infected person in the 14 days before the onset of symptoms of Covid-19.
It is not the first time that the possibility of an incubation reaching 20 days has been mentioned in China. This was already the case in a study by a group of different Chinese researchers, which was the subject of a pre-publication on the medRxiv.org site on February 9.
According to this work on 1099 patients hospitalized in more than 550 different establishments, the incubation period could reach 24 days and the median period would be of the order of three days. This means that half of the patients develop symptoms of the coronavirus within three days of infection.
"Fourteen days is a long time already"
This study must still be evaluated by a committee of peers to be completely validated and "should not be used to guide clinical practices", it is underlined. For now, it is too early to review the incubation time, according to the Directorate General of Health. "If scientific and consolidated data were to come in the coming days, we would assess it in conjunction with the WHO and the ECDC," she said.
The incubation period is a crucial issue in order to stop the spread of Covid-19 since it largely conditions the duration of quarantine. The hundreds of French people evacuated from Wuhan must spend 14 days isolated from the rest of the world. Quarantine was also set at 14 days in Japan for Diamond Princess passengers.
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Should we then extend this quarantine if it ends before the symptoms appear? Here again, everything depends on the exceptional nature or not of these long-term cases. “We are not going to change the length of the quarantine for an isolated case. Fourteen days is already a very long time for people in quarantine and the health services who have to ensure follow-up, ”recalls Arnaud Fontanet. "If other similar cases occur, we could add a message of vigilance in the event of symptoms after this quarantine, which is probably already done in many places. "
