An analysis of publicly available data on infections from the new coronavirus, SARS-CoV-2, that causes the respiratory illness COVID-19 yielded an estimate of 5.1 days for the median disease incubation period, according to a new study led by researchers at Johns Hopkins Bloomberg School of Public Health.
This median time from exposure to onset of symptoms suggests that the 14-day quarantine period used by the U.S. Centers for Disease Control and Prevention for individuals with likely exposure to the coronavirus is reasonable.
Understanding the latency of the disease is key to controlling transmission. It specifically refers to the interval from the initial exposure to the pathogen to the host's symptoms, and there are great differences between different diseases.
Scanning electron microscope image (from: NIAID-RML)
In contrast, the incubation period for influenza is 1 to 3 days, and that for measles is 9 to 12 days. The new study examined 181 confirmed cases of COVID-19 and concluded that 97.5% of people infected with coronavirus will develop symptoms within 11.5 days.
It should be noted that this does not mean that all patients can return to normal immediately after five days, but instead strengthens the currently established two-week optimal isolation observation period for suspected cases.
Exposure (blue) / onset (red) / detection (green) time of 181 confirmed patients
“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 cases would be missed over the long-term,” says study senior author Justin Lessler, an associate professor in the Bloomberg School's Department of Epidemiology.
As Lessler points out, new research confirms that only very few cases may have an incubation period of more than 14 days. Estimates indicate that, of 10,000 subjects, 101 may develop symptoms after 14 days.
Characteristics of COVID-19 confirmed patients (n = 181)
However, researchers also considered the social and economic costs of quarantine and suggested that localities weigh the advantages and disadvantages with reference to the possible consequences of suspected cases.
For example, in some high-risk areas, active isolation monitoring is recommended for more than 14 days. For example, there are medical staff who have contacted clear cases without wearing protective equipment.
Cumulative distribution function of COVID-19 latency estimated from a log-normal model
Jonathan Ball, a professor of molecular virology at the University of Nottingham, points out that trying to pinpoint the source of an infectious disease is clearly a tricky challenge. As a last resort, we can only take a more conservative response.
Details of the study have been published in the recently published Annals of Internal Medicine. You can find it here: link.
The original title was "The Incubation Period of Coronavirus Disease 2019 (COVID-19) From Publicly Reported Confirmed Cases: Estimation and Application".
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