According to a new study led by researchers at Johns Hopkins University, analysis of publicly available data on infections with the new coronavirus, SARS-CoV-2, which causes the respiratory disease COVID-19 has concluded an estimate of 5 , 1 days for the mean incubation period of the disease. This median time from exposure to onset of symptoms suggests that the 14-day quarantine period used by the Centers for Disease Control and Prevention for people with probable coronavirus exposure is reasonable.
By recording the time of possible exposure, onset of symptoms, onset of fever and detection by the authorities for each specific case, American scientists created a model for the distribution of the incubation period , which is nothing other than the time between the time an individual is exposed to the disease and the time they begin to show symptoms. This usually occurs before the contagious period, when transmission of the disease to other people is likely to occur.
Analysis suggests that approximately 97.5% of people who develop symptoms of SARS-CoV-2 infection will do so within 11.5 days of exposure. The researchers estimated that for every 10,000 individuals quarantined for 14 days, only 101 would develop symptoms after being released from quarantine.
For the study, the experts analyzed 181 cases from China and other countries that were detected before February 24, were documented in the media and included probable dates of exposure and appearance of symptoms. Most of the cases were integrated from or to Wuhan, the Chinese city center of the epidemic whose global outbreak of infection emerged in December 2019.
“Based on our analysis of publicly available data, the current recommendation of 14 days for active monitoring or quarantine is reasonable, although with that period some long-term cases would be lost ,” says Justin Lessler, associate professor in the Department of Epidemiology of the Bloomberg School and leader of the study that publishes the Annals of Internal Medicine.
The numbers
The Johns Hopkins team found that less than 2.5% of those infected would show symptoms in 2.2 days; the mean estimated incubation period was 5.1 days; and 97.5% will show symptoms within 11.5 days.
There has been concern that the incubation period was not long enough, after other teams of researchers discovered incubation periods that lasted up to 19 and 24 days.
5.1 days on average, but there may be relapses
“A study carried out among patients who left the hospital in the province of Canton found that 14% of the cases tested positive again . For this reason, in Wuhan they have decreed 14 days of isolation for patients who are considered already cured. For this reason, it is now suspected that the maximum incubation period for the coronavirus may be up to 24 days, and not 14, ” Daniel Orts , a preventive physician and popularizer, explains to MUY.
More research, with larger groups, will be needed to confirm whether a longer incubation period may cause a problem for our current quarantine policies. Either way, if you feel sick, stay home.
Referencia: The Incubation Period of Coronavirus Disease 2019 (COVID-19) From Publicly Reported Confirmed Cases: Estimation and Application. Annals of Internal Medicine (2020). annals.org/aim/article/doi/10.7326/M20-0504
