Coronavirus: People can have disease and not show symptoms for five days, study finds

Current quarantine period is likely correct, research suggests

Andrew Griffin@_andrew_griffin
Monday 09 March 2020 22:00
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Coronavirus cases: The spread outside China

People can have the new coronavirus and not show symptoms for five days, according to a major new study.

The average disease incubation period takes 5.1 days, according to the new research carried out by Johns Hopkins Bloomberg School of Public Health and published today in the journal Annals of Internal Medicine.

Scientists used publicly available data about the spread of the disease – including news reports, public health reports and press releases from a wide range of countries across the world – in an attempt to understand how long the disease takes to manifest, from first exposure to showing symptoms.

They looked at 181 cases that were detected before 24 February. They then picked through reports to find those cases that had detailed information about when those people were probably first exposed and then when their symptoms began.

Most of the cases explored were related to Hubei, the province where the disease is thought to have begun, and its capital city Wuhan. For the most part they had either travelled to or from the region, or had been exposed to people who had done so.

The new estimate will allow researchers to get a better picture of how the outbreak is likely to spread, and how best to contain it through quarantine and other measures.

The analysis showed that 97.5 per cent of people who will go on to get symptoms of the disease will get them within 11.5 days of first being exposed. The researchers estimated that if 10,000 people were put into quarantine for two weeks, only about 101 of them would develop their symptoms after being released.

That suggests the current advice of a 14 day quarantine period looks to be right, the authors note.

“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,” senior author Justin Lessler, an associate professor in the Bloomberg School’s Department of Epidemiology, said in a statement.

The new estimate is broadly in line with previous indications of how long the symptoms of the new virus take to appear, despite the fact those had been based on fewer cases.

It is also largely the same as the incubation period for the version of coronavirus that led to the Sars outbreak in the early 2000s, and at the shorter end of the disease known as Middle East Respiratory Syndrome, which continues to spread across the region. The incubation period is longer than that for the human coronaviruses that cause common colds, which usually take around three days from exposure to first symptoms.

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