Coronavirus infection may start showing symptoms in five days: Study

Using publicly available data on the novel coronavirus, researchers have estimated that the average incubation period -- from the point of infection to the onset of symptoms -- for the deadly disease caused by the virus is 5.1 days.

According to the study, published in the journal Annals of Internal Medicine, this median time, from exposure to the onset of symptoms, suggests that the 14-day quarantine period used by several public health measures across the world is reasonable.

The analysis by researchers, including those from the Johns Hopkins University in the US, also suggested that about 97.5 per cent of people who develop symptoms of the coronavirus -- SARS-CoV-2-- infection will do so within 11.5 days of exposure.

They estimated that for every 10,000 individuals quarantined for 14 days, only about 101 would develop symptoms after being released from quarantine.

In the study, the scientists analysed 181 cases from China and other countries that were detected prior to February 24, were reported in the media, and included likely dates of exposure and symptom onset.

They said most of the cases involved travel to or from Wuhan, China, the city at the center of the epidemic, or exposure to individuals who had been to Hubei, the province for which Wuhan is the capital.

Many public health authorities around the world have been using a 14-day quarantine or active-monitoring period for individuals who are known to be at high risk of infection due to contact with known cases or travel to a heavily affected area, the study noted.

"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," said study senior author Justin Lessler from Johns Hopkins University.

So far, the global outbreak of SARS-CoV-2 infection which emerged in December 2019 in the Chinese city of Wuhan has resulted in more than 1,19,000 officially confirmed cases around the world, and over 4,300 deaths from pneumonia caused by the virus.

The researchers explained that an accurate estimate of the disease incubation period makes it easier for epidemiologists to gauge the likely dynamics of the outbreak, and allows public health officials to design effective quarantine and other control measures.

They said quarantines slow and may ultimately stop the spread of infection, even if there are some outlier cases with incubation periods that exceed the quarantine period.

According to the scientists, sequestering people and preventing them from working has costs -- both personal and societal -- which is perhaps most obvious when health care workers and first responders like firefighters are quarantined.

They came up with a new estimate of 5.1 days for the median, or the typical, incubation period of SARS-CoV-2, similar to estimates from the earliest studies of this new virus, which were based on fewer cases.

The study noted that this incubation period for SARS-CoV-2 is in the same range as SARS-CoV -- a different human-infecting coronavirus that caused a major outbreak centered in southern China and Hong Kong from 2002-04.

MERS-CoV, a coronavirus that has caused hundreds of cases in the Middle East, has an estimated mean incubation period is 5-7 days, the scientists said.

Lessler and his colleagues have also published an online tool which allows people to estimate how many cases would be caught and missed under different quarantine periods.